1. Snake plant (Sansevieria trifasciata)
2. Red-edged dracaena, Dragon tree (Dracaena marginata)
3. Bamboo palm (Chamaedorea seifrizii)
4. Peace lily (Spathiphyllum wallisii)
5. Golden pothos (Epipremnum aureum)
6. Cornstalk dracaena (Dracaena fragrans, syn: Dracaena deremensis)
7. Flamingo lily (Anthurium andraeanum)
8. Lady palm (Rhapis excelsa)
9. Boston fern (Nephrolepis exaltata)
10. Queen Kimberley fern (Nephrolepis obliterata)
11. Chinese evergreen (Aglaonema modestum)
12. Spider plant (Chlorophytum comosum)
13. Benjamin fig (Ficus benjamina)
14. Purple heart plant (Tradescantia pallida, syn Setcreasea purpurea)
15. Bromeliad, Scarlet star (Guzmania lingulata)
16. English ivy (Hedera helix)

 

Is there anything common between your house and a spaceship? Yes, it’s air pollution.

We usually think of air pollution as being outdoors, but the air in your house or office is also polluted. Indoor air pollution may be as much or more of a problem as pollution outdoors, according to new research. Those who live in cities spend up to 90 percent of their time indoors — most of the air they are breathing is “indoor air.”

“When we think of the term ‘air pollution,’ we tend to think of car exhausts or factory fumes expelling gray smoke,” said study co-author Prashant Kumar of the University of Surrey. “However, there are actually various sources of pollution that have a negative effect on air quality, many of which are found inside our homes and offices. From cooking residue to paints, varnishes and fungal spores, the air we breathe indoors is often more polluted than that outside.”

Modern building can have unintended side effects. One of these side effects is less air flow. Lack of air flow allows for indoor air pollution to build up and cause health issues like asthma or sick building syndrome.

In fact, modern furnishings, synthetic building materials, and even your own carpet may carry more chemicals than expected. These chemicals can make up to 90 percent of indoor air pollution.

According to the U.S. Environmental Protection Agency, the air inside the average home in the U.S. is up to five times more polluted than the air outside. While moderately alarming on a certain level, it’s really more of a catalyst for making positive changes in one’s life that not only freshen up the air, but also allow us to more intimately connect with nature – not merely when we’re outside, but in the comfort of our own living and working spaces. The remedy? Consider air-purifying plants.

One indoor contaminant of particular concern is formaldehyde, which is released by many household products, among them pressed woods, some types of foam insulation, paper products, some paints and varnishes, and permanent-press fabrics. The National Toxicology Program lists formaldehyde as reasonably anticipated to be a human carcinogen.

Briefly, your house and office have the following pollutants:

What are the effects?

Sometimes a group of people have symptoms that seem to be linked to time spent in a certain building. There may be a specific cause, such as Legionnaire’s disease. Sometimes the cause of the illness cannot be found. This is known as sick building syndrome.

Usually indoor air quality problems only cause discomfort. Most people feel better as soon as they remove the source of the pollution. However, some pollutants can cause diseases that show up much later, such as respiratory diseases or cancer.

Each pollutant is harmful in a different way, at a different concentration. Studies have determined such a concentration causes such symptom, but this is in theory. In reality, pollutants concentrations in your house or your office does not cause immediate problem, so you do not feel anything amiss. But who knows what will happen 10, or 20 or 30 years later, you spend 22 hours each day inhaling such toxic pollutants? (and 24 hours a day if your city air is also polluted?)

Experts agree on one point: you should find ways to reduce to the extent possible the air pollutants in your home and office. One way is to provide air circulation, and even better, get sunlight. The other way is to have plants.

NASA Clean Air Study

The NASA Clean Air Study was led by the National Aeronautics and Space Administration (NASA) in association with the Associated Landscape Contractors of America (ALCA). As NASA researchers explored the possibilities of long-term space habitation, it became evident that the air in a tightly sealed space capsule would quickly become contaminated with volatile organic compounds (VOCs) and other chemicals released by the materials used to manufacture the capsule interior.

The NASA Clean Air Study results suggest that certain common indoor plants may provide a natural way of removing toxic agents such as benzene, formaldehyde and trichloroethylene from the air, helping neutralize the effects of sick building syndrome.

The first list of air-filtering plants was compiled by NASA as part of a clean air study published in 1989, which researched ways to clean air in space stations. As well as absorbing carbon dioxide and releasing oxygen, as all plants do, 29 species and cultivars can eliminate significant amounts of benzene, formaldehyde and trichloroethylene. The second and third lists are from B. C. Wolverton’s book and paper, and focus on removal of specific chemicals.

NASA researchers suggest efficient air cleaning is accomplished with at least one plant per 100 square feet of home or office space. Other more recent research has shown that micro-organisms in the potting mix (soil) of a potted plant remove benzene from the air, and that some plant species also contribute to removing benzene.

NASA had a small problem on their hands when it came to long-period manned space missions. They needed an efficient, lasting source of clean air to keep astronauts alive and thriving during extended interstellar travel. What they discovered is that a few common houseplants, and one in particular – Snake plant (Sansevieria trifasciata) – did the job wonderfully and were also powerful air purifiers to boot.

Based on this research, some scientists say house plants are effective natural air purifiers. And the bigger and leafier the plant, the better. “The amount of leaf surface area influences the rate of air purification,” says Bill Wolverton, a former NASA research scientist who conducted that 1989 plant study.

Wolverton says that, absent expensive testing, it’s impossible to guess how many plants might be needed to clean a room of its contaminants. But he usually recommends at least two “good sized” plants per 100 square feet of interior space. “The Boston fern is one of the most effective plants for removing airborne pollutants, but it is often difficult to grow indoors,” he says. “I usually recommend the golden pothos as my first choice, since it is a popular plant and easy to grow.”

The NASA study has been the basis for newer studies about indoor plants and their air cleaning abilities. While plants have less horse power than air purifiers, they’re more natural, cost effective, and therapeutic.

Research at University of Georgia

The research at University of Georgia, led by Prof Stanley Kays, tested 29 plant species exposed with five volative organic compouna: như enzene, toluene, octane, alpha-pinene and TCE (trichloroethylene). The results were release on 2009, indicating 5 best air-purifying plangs:

• Purple heart plant (Tradescantia pallida), the best on air purification versality.
• Waffle plant (Hemigraphis alternata, syn.: Hemigraphis colorata, Ruellia alternata)
• English ivy (Hedera helix),
• Variegated wax plant (Hoya cornosa)
• Asparagus fern (Asparagus densiflorus)

Research at State University of New York

The State University of New York researchers said: “Buildings, whether new or old, can have high levels of VOCs in them, sometimes so high you can smell them.” So they conducted precise experiments to determine the efficiency and capabilities of five different types of houseplants – the jade plant, spider plant, bromeliad, dracaena, and Caribbean tree cactus. Each plant was placed in an air-tight chamber with specific concentrations of several types of VOCs. By measuring the air quality over time, the researchers were able to see which did the best job of purifying the air.

The bromeliad plant (Guzmania lingulata) got a gold star from the team, managing to clean up 80 percent of the pollutants in six of the eight VOCs tested. Others scored highly for certain pollutants: the corn plant (Dracaena fragrans) absorbed 94 percent of the chemical acetone, used in nail polish remover. The spider plants (Chlorophytum comosum), meanwhile, were very fast at removing VOCs, starting work just a few minutes after being placed inside its container.

Compiling the understanding

An article by TIME on 17-Jan-2018 compiles the understanding on the benefits of indoor plants.

While Wolverton has long been a vocal advocate of indoor plants – he’s written books on the topic, and now operates a consulting company that advocates for the use of plants to clean contaminated air – other experts say the evidence that plants can effectively accomplish this feat is far from conclusive.

“There are no definitive studies to show that having indoor plants can significantly increase the air quality in the home to improve health in a measurable way,” says Luz Claudio, a professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai.

Most research efforts to date – including the NASA study – placed indoor plants in small, sealed environments in order to assess how much air-scrubbing power they possessed. But those studies aren’t really applicable to what happens in a house, says Stanley Kays, a professor emeritus of horticulture at the University of Georgia.

Kays coauthored a 2009 study on the air-cleaning powers of 28 different indoor plants. While many of those plants could remove toxins from the air, “moving from a sealed container to a more open environment changes the dynamics tremendously,” he says.

In many cases, the air in your home completely turns over—that is, swaps places with outdoor air—once every hour. “There’s a phenomenal amount of air coming in and going out in most houses,” Kays says. “From what I’ve seen, in most instances air exchange with the exterior has a far greater effect on indoor air quality than plants.”

Also, plants used in lab studies are grown in optimal conditions. They’re exposed to ample light in order to maximize photosynthesis, which improves a plant’s toxin-degrading abilities. “In the home, this isn’t the case at all,” Kays says. “The amount of light in many parts of a house is often just barely sufficient for photosynthesis.”

He knows many people will be disappointed by what he has to say, and he wants to make it clear he believes house plants are not only pleasant living companions, but that they also provide a number of evidence-based health benefits. Studies have shown plants can knock out stress by calming the sympathetic nervous system, and can also make people feel happier. More research shows spending time around nature has a positive effect on a person’s mood and energy levels.

“There are some real plusses to having plants around,” Kays says. “But at this time, it doesn’t look like plants sitting passively in a house are effective enough to make a major contribution to purifying indoor air.”

Benefits of indoor plants

Various studies indicate that indoor have benefits other than air purification.

Plants give an assist in breathing. Inhaling brings oxygen into the body, exhaling releases carbon dioxide. During photosynthesis, plants do the opposite, of sorts: They absorb carbon dioxide and release oxygen, making plants and people great partners when it comes to gasses. Plants help to increase oxygen levels, and our bodies appreciate that.

But here’s something to know: When photosynthesis stops at night, most plants switch things up and absorb oxygen and release carbon dioxide. However, a few special plants – like the snake plant (Sansevieria trifasciata), the spider plant (Chlorophytum comosum) and the bromeliad (Guzmania lingulata) – flip that script and take in carbon dioxide and release oxygen. Meaning, use these plants in bedrooms to keep the oxygen flowing at night.

Plants help reduce stress and create a feeling of well-being. Most of us know instinctively that being close to greenery makes us feel more at ease with our surroundings. We experience less stress when there are plants around us. Buildings are quieter and more relaxed but, at the same time, more stimulating and interesting. A substantial body of academic research has shown conclusively that interior landscaping has dramatic effects on the wellbeing of building occupants. People in offices are more productive, take fewer sick days, make fewer mistakes, and they are happier when interior landscaping enhances their environment. Patients in hospitals benefit greatly from being more in touch with nature. There is even evidence showing students perform better in improved learning environments.

Plants help deter illness. In the great outdoors, plant roots tap the groundwater table for water which then evaporates through its leaves in a process known as transpiration. Studies show that this accounts for about 10 percent of the moisture in the atmosphere! The same thing happens at home (minus the groundwater table part), which increases the humidity indoors. While this may sound unappealing during hot moist months, it’s a gift during drier months or if you live in an arid clime. According to Bayer Advanced, studies at the Agricultural University of Norway document that using plants in interior spaces decreases the incidence of dry skin, colds, sore throats and dry coughs. And other research reveals that higher absolute humidity is conducive for decreased survival and transmission of the flu virus.

Plants boost healing. Bringing flowers or a plant while visiting a hospital patient may be verging on cliché, but so effective are plants in helping surgery patients recover that one study recommends them as a “noninvasive, inexpensive, and effective complementary medicine for surgical patients.” Plants as medicine! The study, conducted at Kansas State University, found that viewing plants during recovery from surgery led to a significant improvement in physiologic responses as evidenced by lower systolic blood pressure, and lower ratings of pain, anxiety, and fatigue as compared to patients without plants in their rooms.

Another technique to decrease recovery time, as noted by Texas A&M University, is horticulture therapy in which patients are tasked with taking care of plants. The patients who physically interact with plants experience a significantly reduced recovery time after medical procedures.

Plants help you work better. A number of studies with both students and workers reveals that studying or working in the presence of plants can have a pretty dramatic effect. As with simply being in nature, being around plants improves concentration, memory and productivity. Being “under the influence of plants” can increase memory retention up to 20 percent, according to a University of Michigan study.

Also, two Norwegian studies found that worker productivity is greatly enhanced by the presence of plants in the office. “Keeping ornamental plants in the home and in the workplace increases memory retention and concentration,” notes Texas A&M. “Work performed under the natural influence of ornamental plants is normally of higher quality and completed with a much higher accuracy rate than work done in environments devoid of nature.”

Introducing indoor plants for your home and office

As clarified above, we should recognize the various benefits of indoor plants, from physical to mental health. So you should have indoor plants in your rented house or your condominium. You should also encourage or make decision on having indoor plants in your office.

The introduced indoor plants are selected based on the following criteria:

• The plants can purify at least two chemical compounds in the NASA research, or are the best in other studies.
• The plants are perennial, to avoid the labor and cost in procuring new plants after each several months. This is why the writer eliminates the Barberton daisy (Gerbera jamesonii) and the florist’s chrysanthemum (Chrysanthemum morifolium) even though these two species are among the best air-purifiers. What is hard to understand is that NASA studies the plant species that can live in some months for use on spaceships that travel for years (?!)
• The plant is slow growing and does not have a spreading foliage. Based on this criterion, for example, the areca palm (Dypsis lutescens) and the dwarf date palm (Phoenix roebelenii) are not recommended: these two plants have a tendency to grow high such that they need big and heavy pots and are more suitable outdoor (but they are suitable for a space station?!)
• The plant is common and readily available, proven to be suitable for indoor conditions oaf light, humidity and temperature. Based on this criterion, the lilyturf (Liriope spicata) is not recommended: it is not available widely, and information as an indoor plant is scarce.
• Studies indicate that the higher total leaf surface the better. Based on this criterion, the aloe vera (Aloe vera) is not recommended.
• The plant is easy to grow and requires little care.

From the above-mentioned criteria, even though NASA Study covers nearly 30 species, the writer selects the following soecies, in the order from the more desirable.

1.     Snake plant (Sansevieria trifasciata)

This is the top house plants for clean indoor air in NASA Clean Air Study that used the cultivar Sansevieria trifasciata ‘Laurentii’.

Are you looking for a diehard houseplant? The snake plant or mother in law tongue is the plant for you. Always stylish, this plant is a top choice for indoor gardening, as it can thrive in a range of lighting conditions and handle dry soil. They’re virtually indestructible unless you have a heavy hand with the watering can or place them in a hot, sunny window.

These evergreen perennials are very long-lived, unlike some houseplants. If you’re looking for your own snake plant, there are many different species and varieties on the market with more being introduced each year. You can find them tall or short, with round, flat or concave leaves, and variegated with dark green, silver, light green, yellow, chartreuse or white.

Picture: 3 ways to arrange snake plants. The cultivar Sansevieria trifasciata ‘Laurentii’ is on the bottom.

Snake plant is also known as Mother-in-law’s tongue indoor plant. It can grow under low light and improper watering. You should prefer to keep this plant in bedroom – 2 plants at least – since it releases oxygen at night. It purifies air by absorbing formaldehyde, nitrogen oxides, trichloroethylene, xylene, toluene and benzene..

Soil: because root rot is one of its main issues that kill these plants, a fast and well-draining soil is recommended to help prevent this.

Light: even though Sansevierias prefer medium light (which is about 3 m away from west or south window), they’ll also tolerate low light and high light. Just be sure to keep them out of the direct sun because they’ll burn in a heartbeat.

Water: easy does it with the watering. You want to be careful not to overdo it because your plant will rot out, as shown by brown spots on the leaves. Always make sure the soil is almost completely dry before thoroughly watering again. Water your snake plants every 2-6 weeks, depending on your home’s temperature, light levels, and humidity. So, if you travel or tend to ignore plants, this is the one for you.

Fertilizer: an organic all-purpose houseplant food would be fine. Just be sure to fertilize in the spring and/or summer, twice at the most. Lightly fertilize with a liquid 20-20-20 fertilizer of 1/2 strength.

Propagation: once you’ve got a snake plant you may never need to buy another one. They’re very easy to propagate. In the garden they’ll propagate on their own, spreading by underground rhizomes. As a houseplant, division followed by leaf cuttings are the easiest ways.

Care: repot mine 2-5 years at the most. If the plant is growing in low light, transplanting every 5-10 years will be fine.

2.     Red-edged dracaena, Dragon tree (Dracaena marginata)

This is one of top 10 house plants for clean indoor air in NASA Clean Air Study. Of all the Dracaenas the marginata is probably the most versatile. Some confuse this houseplant with a palm. It is rugged and carefree as an indoor plant adding a tropical appearance to any room it graces. One big advantage most all the Dracaenas provide for use as a house plant is the small footprint. You can get a tall upright 2-m character plant which uses very little floor space, eventually it will grow 2.5-4.5 mt high and 1-2.5 m wide in the right conditions.

The leaves are quite slim. There are three types, one has a dark red outer edge leaves with a green center, another is green in the center with red and yellowish stripes, and the other the colorama has thick red edges. The leaves are produced when the trunk grows stems (cane) from the side that often needs to be trained (keeps them growing upwards). These stems have a grayish brown bark (the trunk) that can also produce smaller ones, so the dragon tree really needs to be pruned to avoid the plant from growing in all directions. Using canes of various lengths either straight, with bends and curves or multiple heads and planting the canes together allows growers to produce fuller plants.

These are slow grower’s that can take about 10 years to reach over 1.5-m tall, but look lush once they reach about a foot high. They have a very similar look like palm tree plants.

Plants with thin, spiky leaves add drama to your interior, thanks to their bold silhouettes. A strong filterer, the red edge dracaena removes benzen, formaldehyde, trichloroethylene, xylene, and reduces electromagnetic radiation.

Soil: organic well-drained.

Light: bright light, yet out of direct sunlight. It will handle lower light levels, but the leaves will be thinner.

Water: keep the soil damp but not soggy, as too much water is a kiss of death for this plant. allow the plant to dry out a little between waterings. When the soil surface is dry to the touch – water the plant thoroughly and allow the excess water to exit through the drainage holes. Dracaenas are also very fluoride sensitive. This often shows up in yellowing on the leaf tips.

Fertilizer: most plants you buy for the home will have enough fertilizer to last a long time – in general, stay away from fertilizing indoor plants but if you must, use a weak liquid fertilizer at 1/4 to 1/3 strength will do.

Propagation: use stem cuttings to propagate a dracaena marginata.

Care: the leaves of any Dracaena over time will grab their share of dust. If the plant’s stems become too long and bare, cut them off at the desired height. From the cut will sprout one or more new shoots that will grow leaves, and new leaves will soon appear.

3.     Bamboo palm (Chamaedorea seifrizii)

This is one of top 10 house plants for clean indoor air in NASA Clean Air Study.

This sturdy plant is known for its easy elegance and height. It can be 4-6 feet or 1.2-1.8 m tall indoors, with a spread of around 3 to 5 feet or 0.9-1.5 m. Big plants transpire a high dose of moisture into the air, making it a welcome addition in dry winter months in temperate zones (like North Vietnam) but undersirable in humid zone (like South Vietnam).

This slow growing plant is very easy to grow and maintain. As with most palms, the soil. Applying fertilizer in the summer months will keep these palms green and healthy. Keep evenly moist but not consistently wet, and mist occasionally to prevent spider mites.

This popular house plant is a suckering species (multi-stem palm). It naturally produces more than one vertical stem or trunk. Although new trunks emerge from the bottom of the first trunk and grow, the first trunk, the tallest of all trunks until the plant reaches maturity, is easily detectable. New trunks continue to form throughout its life. However, formation of new stems may slow down over time.

Be sure to keep the leaves and soil clean, so the plant is in optimal, healthy condition to help clean your indoor air.

Soil: should be well drained. Keep it evenly moist but not consistently wet, and mist occasionally to prevent spider mites. Adding some large-grain sand to the soil can make it well-aerated and can promote quick drainage. The soil should retain some water too. Use a well-drained potting mix.

Water: this plant likes to stay uniformly moist, remember that’s moist NOT wet. When the soil has dried down about one third or half way down from the top you should water the complete top of the soil. Make sure the excess water that can accumulate in the bottom of the planter is removed. These plants do not like to sit in water. If you are over watering, you’ll usually notice the leaf tips begin to turn yellow and fall off from the stems as well as the new growth coming out very pale. The plant may also experience stem rot. On the other side if you’re under watering the tips of Seifrizii will turn brown as well as the new growth.

Light: it will grow in low light conditions, although it will grow taller with more light. Each week bring the plant to direct sunlight for at least 60 minutes.

Fertilizer: granular, slow-release fertilizer. Seifrizii is sensitive to soluble salts, so remove the time-release fertilizer from the top of the pot and leach the soil thoroughly with water. Allow the plant to completely drain.

Propagation: by seeds which takes around 6 months or more to germinate, or by repotting small plants growing from the rhizomes.

Care: overall this plant doesn’t require much care to maintain its gorgeous tropical appearance.

4.     Peace lily (Spathiphyllum wallisii)

This is one of top 10 house plants for clean indoor air in NASA Clean Air Study.

Of all the flowering house plants, peace lily care is probably the easiest. In fact, it tolerates average indoor conditions better than many house plants. Blooms usually appear in early summer and last for weeks. The pale green spathe turns white as it opens and surrounds the protruding spadix that is densely covered by its tiny, true flowers. Dark-green, glossy leaves are strongly veined and arch away from the plant’s base, making this an attractive foliage plant when not in bloom.

Peace lilies cleanse your home of pollutants like acetone – a carcinogen commonly found in nail polish and paint.

It is a plant which can be maintained very easily. It requires very less water and fertilizer. It can survive in dry soil for long time. In moderate light conditions, this plant will bloom with white flowers , but too little light can prevent flowers from blooming. It can be used as air purifier. Since it removes mold spores from air, it is best suited for bathrooms.

Soil: Peat moss-based potting mix.

Light: this plant survives with very little sunlight. Plants that fail to bloom usually aren’t getting enough sunlight. Move your plant to a brighter location, but keep it out of direct sun, which can scorch leaves.

Water: watering about once a week. Water thoroughly, but don’t allow the soil to get soggy.

Care: When flowers start to fade, cut off the flower stalks as close to the base as possible. Keep the leaves dust-free by wiping them with a damp cloth. When caring for peace lily plants, remember that its leaves will indicate any problems. Brown leaf tips are likely caused by overwatering. It could also be caused by direct sun. Move it to a shadier spot and be careful not to overwater. If the leaves become shriveled and dry, the humidity is too low. You can increase humidity by misting the plant or placing it on a tray of wet pebbles. Got an older plant that refuses to bloom? If you haven’t divided it in several years, divide it in spring. This is one of the few plants that blooms better after dividing it.

Propagation: Division. Early spring is the best time to divide Spathiphyllum because it is beginning its most vigorous time of growth. Divide it every 5 years or when necessary.

5.     Golden pothos (Epipremnum aureum)

This is one of top 10 house plants for clean indoor air in NASA Clean Air Study.

Extremely easy to grow. Golden pothos is a popular house plant well known for its long, trailing stems that can grow to 8 ft (2.4 m) or more. Glossy, heart-shaped leaves emerge green and become variegated with yellow or white. Show off those beautiful trailing stems in a hanging planter. Or you can train it to climb. A tree-climber in its native tropical habitat, this plant has aerial roots that can be trained to climb a moss stick or trellis. Use florist wire to hold the vines while they grow and wrap themselves around the support.

Also known as devil’s ivy, this plant may be as close as plants can get to indestructible. It flourishes in a variety of conditions and can grow up to 2.5-m long. It’s also considered one of the most effective indoor air purifiers for removing common toxins. If you are pretty busy with your life schedule but still want to grow some air purifying plants inside your house, then golden pothos are just perfect for you. You just need to water these plants once in two weeks. Again, these grow efficiently in the room temperatures..

Soil: Good-quality all-purpose potting mix.

Light: Although this plant tolerates low light well, its leaves may lose their variegation when they don’t get enough light. It will look its best in moderate or bright light. It makes an excellent office plant because it grows well under fluorescent lights.

Water: Allow the top 1 in (2.5 cm) of soil to dry between waterings. It will not tolerate soggy soil. Overwatering will cause leaves to turn yellow and fall off. Use a pot with a drainage hole.

Fertilizer: Feed every 2 weeks spring through fall with a balanced liquid fertilizer diluted by half. In winter, feed monthly.

Propagation: Stem tip cuttings root easily in water or moist perlite or vermiculite. Cut a 4-6-inch stem tip with a couple leaves attached. It takes at least 4 weeks to root.

Care: Stems that are allowed to grow longer than 4 ft (1.2 m) often shed most of their leaves near the base of the plant. It’s a good idea to trim off long stems once in a while to keep pothos leafy and full. Cut stems back a couple times a year to keep the plant bushy and full. Cutting right after a leaf node (the place where the leaf is attached to the stem) will encourage the stem to branch out, giving you a fuller plant.

6.     Cornstalk dracaena (Dracaena fragrans, syn: Dracaena deremensis)

This is one of top 10 house plants for clean indoor air in NASA Clean Air Study.

NASA studies on 3 cultivars named Cornstalk dracaena (Draceaena fragrans ‘Massangeana’), Janet Craig (Dracaena deremensis ‘Janet Craig’) và Warneckei (Dracaena deremensis ‘Warneckei’). All three cultivars are equally good Iin removing benzene, formaldehyde và trichloroethylene, and toluene/xylene.

This plant grows with one or more canes (stems) and then produces new stems and a crown of leaves near the top of the cane. These canes can grow up to 6 ft or more indoors or they can be cut at the top as soon as they reach a suitable height. The corn plant produces fragrant flowers in it’s natural habitat of temperte climate, but it’s not likely to bloom indoors – although they can. It’s the foliage that’s the real attraction for this plant.

The most popular types of leaves on the D. fragrans can be green on the outer edge and yellow in the center (D. fragrans ‘Massangeana’), or yellow and green striped edges with green in the center (D. fragrans ‘Lindenni’). The broad and glossy lanceolate leaves arch over and sit nicely within a rosette.

Soil: Most well draining potting soil mix types are fine to use.

Light: A good mix of sun shine and shade is ideal for this dracaena, but hardly any direct sunlight. Although it grows quicker and better in bright light you’ll also find it survives and grows well enough in low light conditions.

Water: eep the soil slightly damp to the touch and in the winter slightly dry.

Care: You will find the lower leaves on this plant turn yellow after a period of time which is normal, and the leaves on this plant only have a life span of 2-3 years anyway. Remove the lower leaves when they begin to yellow. You can also cut the top of a cane (stem) when it has reached the height you wish it to grow up to and re-plant the cutting.

Propagation: These are quite easy to propagate from stem tip cuttings, best done in spring or summer. You can also cut a new or old rosette and re-plant it. After replanting keep the soil moist and mist the leaves which will encourage the plant to grow.

7.     Flamingo lily (Anthurium andraeanum)

This is one of top 10 house plants for clean indoor air in NASA Clean Air Study.

Anthurium scherzerianum and Anthurium andraeanum lend their common name, flamingo lily, from their brightly colored waxy flowers. These are jungle plants that live protected from the sun by a canopy of trees. Anthurium andraeanum is much more common. It grows a little larger and its spadix (the part that sticks out of the flower) is straight, whereas that of Anthurium scherzerianum is usually curly.

They are appreciated for their exotic looks and, when their needs are met, can bloom year-round. A great choice for any houseplant lover looking for a pop of color in their home! This exotic flowering plant prefers a warm and shady environment.

Soil: well-draining peat moss-based soil type. Add a little charcoal to the potting mix.

Light: although flamingo lilies love bright light, they do not appreciate direct sunlight at all and burn easily. A spot near a window that never gets direct sun in a relatively humid location (such as the kitchen or bathroom) should work well.

Water: watered regularly and thoroughly, allowing the soil to only dry slightly before watering again. These plants like evenly moist soil, especially during summertime, but absolutely do not appreciate wet feet. When left in standing water for too long their roots can quickly develop rot. They can be left to dry out a little more during winter when the plant isn’t growing as much. Daily misting helps to prolong the flowers.

Fertilizer: lightly feed it with a diluted fertilizer around every two weeks or so.

Care: Flamingo lilies don’t have to be repotted very often. You can usually repot them during springtime every 2-3 years; when doing so you can either move one pot size up or divide the plants and plant them separately. When re-potting your Anthurium, use care to avoid damaging the fragile roots. Choose a high quality, peat moss based potting mix, with a high perlite content to ensure proper drainage. Remove spent flower bracts as soon as they begin to fade and turn brown, to encourage continued flowering.

Propagation: the plant can be easily propagated by dividing the root structure when you repot your plant, making sure that each division contains at least two rhizomes..

8.     Lady palm (Rhapis excelsa)

This is one of top 10 house plants for clean indoor air in NASA Clean Air Study.

Rhapis excelsa is the most well-known and widely cultivated species, easily adapting to most interiors

The broadleaf lady palm loves thorough waterings, moist soil and bright, indirect light. However, this plant will tolerate low light, making it easy to grow as a houseplant. Sturdy canes or stems find themselves covered with a fibrous sheath or coarse, dark brown fiber.

Large thick leaves with blunt tips and wide segments, gives Rhapis excelsa its occasional name “broadleaf lady palm”. A prolific producer of rhizome offshoots adds fullness and provides an easy method to increase numbers by division. In addition, seed is occasionally available.

Find a plant that fits an area indoors and you won’t have to worry about the Rhapis outgrowing its space. Generally speaking growers would classify Rhapis as a slow grower. A typical 6–8″ (15-20 cm) potted plant has been growing in the nursery for minimum of 2 years. It is not unusual for the larger sizes to be nursery grown for 4-7 years.

Soil: almost any well-drained soil, density should be firm and allow water to slowly filter through.

Light: the plant grows best in bright, indirect light near a window or skylight but is very adaptable to low light areas.

Water: Rhapis should be thoroughly watered by soaking or drenching the entire root system. They like their soil to stay moist.. Brown leaf damage is usually associated with extreme heat, allowing the plant to dry out, or not thoroughly watering the entire root system. In container grown Rhapis, the roots will be predominately at the bottom of the container rather then throughout. Keep this in mind when checking your soil moisture. The top may be dry but the bottom still wet. Rhapis as are other palms can be sensitive to excess boron, fluoride, and chlorine in water supplies, which will cause fast spreading black tip burn. Use the purest water available until the problem is corrected.

Fertilizer: Rhapis are relatively slow-growing plants and need very little fertilizer. As a guideline, apply only 1/2 the recommended rate required by other plants in your home. Leaf color is one of your best guides:

• Rich green indicates fertilizer levels are adequate
• Slight overall yellowish color may mean the to apply nutrients

Care: New fronds come out from the center of the trunk. Trim off lower leaves as they age and become discolored. Rhapis prefer to be slightly root-bound so repotting every couple years is normal. All roots and the base of canes should be covered to retain moisture.

9.     Boston fern (Nephrolepis exaltata)

The boston fern is readily available, relatively cheap and is a great starter fern if you enjoy the lush green foliage and the feelings of peaceful tranquility they seem to evoke in people. It’s also one of the top rated plants for removing air pollutants from the air.

Because of its almost insatiable appetite for water, it pumps out large amounts of water vapor into the nearby air, thereby increasing humidity. This could be a disadvantage in humid regions.

The boston fern has graceful green, drooping fronds that are naturally cut in such a way to give a ruffled looking effect and therefore it looks really good in a hanging basket or in a place where the fronds can hang down over something, for example on the edge of a bookcase or shelf. It also looks great on a pedestal.

They’re quite sensitive to chemicals and the smoke from coal fires or wood burners are fairly toxic, draughts must also be avoided. This means your choice of placement will need to be considered quite carefully if your home has any of these features.

Water: The soil should be almost always moist. Because Boston ferns tend to be planted in potting mixtures that are high in peat moss, it is a good idea to soak the pot of the Boston fern once a month or so to make sure the peat moss is fully hydrated. Be sure to let it drain thoroughly after this.

Light: medium to bright indirect. Reasonable light levels are needed. A Boston Fern will accept some full sun and some quite shady areas, but for a happy and healthy looking plant you should aim for a fairly bright spot which does not receive harsh sunlight.

Fertilizer: the plant does not need much fertilizer. Fertilizer should only be given to the plant a few times a year.

Propagation: Some owners like to try and propagate by growing the spores which a healthy and mature fern will produce. This is quite complex and time consuming, in addition some plants sold as “Boston Ferns” are not actually pure species and thus the plant won’t produce viable spores anyway.

So it’s usually more productive to divide a large plant into 2 or 3 pieces when you repot, or a more reliable approach is to look out for “baby” ferns appearing on “runners” at the edges of the pot. After they are large enough to handle, they can be cut away from the “runner” and potted up in a similar compost mix.

10.  Queen Kimberley fern (Nephrolepis obliterata)

This hardy fern features leaves that grow in a more upright position than the Boston fern.

Otherwise the air-purifying capacities of the two species are comparable, and care methods are similar.

11.  Chinese evergreen (Aglaonema modestum)

Super-easy to grow, a low-maintenance houseplant, the durable Chinese evergreen is one of the most popular house plants. It tolerates all kinds of conditions, from low light to dry air. you should let the soil dry out a bit between waterings.

The leaves are liner (elongated with parallel sides) or oval shaped which grow at the tip of the stalks. These leaves grow up to 30 cm in length and about 5-8 cm wide.

Soil: well-drained potting soil.

Water: Keep the soil moist at all times. Water it moderately and allow the soil to dry almost completely between watering, with a little regular misting.

Light: the darker the leaves and stalks, the less light is needed. A bright room with the plant sitting in a shaded spot is best. Avoid direct sunlight.

Fertilise: Feed the plant with a diluted balanced liquid fertilizer in the spring and summer

Propagation: by dividing the root with a few stalks and leaves attached.

Care: repotted every few years. The plant likes to become slightly root bound – so don’t worry if it seems to showing some roots through the bottom of the pot.

12.  Spider plant (Chlorophytum comosum)

Cây nhện nằm trong số 10 cây tốt nhất trong nghiên cứu của NASA về tác dụng thanh lọc ô nhiễm không khí.

The spider plant is considered one of the most adaptable of houseplants and the easiest to grow. It is an excellent choice for beginners: this tough little houseplant is not just easy to take care of: it is actually hard to kill!

The slender, arching leaves are dark green with a creamy white stripe. Leaves grow from a central crown and can reach up to 1 ft (30 cm) long. The plant looks great in a hanging basket or on a pedestal.

Soil: good aeration and a well-draining soil will produce good plant growth. Limestone is a good addition to help raise the pH level.

Water: this plant does not require lots of water. Your specific watering schedule will vary depending upon the temperature and level of lighting you maintain. Generally speaking, check the soil weekly by poking it with your finger. If the top inch of soil is dry, give your plant a moderate watering. Avoid using fluoridated water on the plant.

Light: the spider plant should not be exposed to the hot midday sun in the summer to make sure the leaves won’t burn. A half-shaded spot would be all right. In a darker environment and in the shade, however, it grows only slowly.

Fertilizer: the plant does not require lots of fertilizer. It responds well to an application of liquid plant food every few weeks during the spring and summer. Use a good, general purpose, water-soluble houseplant fertilizer. Mix it half strength. The fertilizer you choose should have no fluoride and very little boron. Be sure not to overdo the strength or frequency of fertilizing because this can cause brown leaf tips.

Propagation: Propagating naturally in soil is simple. The plant naturally sends out multiple runners from the mother plant as white, star-shaped flowers become little plants dangling from the end. In the wild, these little plants come in contact with the soil, sink their roots and take off on their own. Replicating this process is easy. Simply clip the little plants off the ends of the shoots with a sharp pair of scissors or pruning shears and set them lightly in loose soil in their own pots, planters or hanging baskets. Keep your little plants in a sheltered area with a consistent temperature and indirect lighting. Water as needed. Before you know it, they will begin to take root and start growing.

If you want to be “more like nature”, set up host pots of soil around your parent plant and guide the babies into their own pots. Peg them in place if needed and firm the soil around them. When they sink roots, cut them loose from the parent by clipping the connecting runner with sharp shears or scissors. Clip close to the baby plant.

Care: Brown leaf tips, a common problem on spider plants, are due to over-fertilization, low humidity, or dry soil conditions.

No blooms? These plants like to be slightly root-bound and will flower and produce plantlets best when grown in a smallish container. Also, take it easy on the fertilizer — too much will produce a lot of leaves, but no flowers and plantlets.

Don’t worry when you begin to see the rhizomes (tubers) protruding from the soil. Simply thin them out with a sharp spade and plant them in new pots (or in the ground during warm weather). There is really no need to replant or repot your original parent plant. It can remain perfectly happy in its original pot indefinitely. Unless they get like the spider plant below which is root bound!

13.  Benjamin fig (Ficus benjamina)

It can grow up to 10′ (3 m) indoor wheareas in the wild some of the tallest ones can reach over 100′ (30 m) tall!

As the plant ages, the leaves will turn a darker green. The leaves have a glossy look to them, almost as if they have been polished.​

This tree loves the light and does not like being moved so it’s best to find a nice sunny spot in your home for it to stay. Make sure that wherever you place your weeping fig tree is free of strong drafts of air — both cold and hot.

Soil: A well-draining soil is best. Benjamin figs don’t like soggy soil at all, and will quickly drop leaves and die if they are watered too often. The soil should dry to at least 1-2″ (2-5 cm) deep before you water them again.

Water: Benjamin fig is very sensitive to chemicals that appear in most tap water. Fluoride, chlorine, and the salts that are in tap water can harm the plant. For best results, water only with filtered or distilled water. If you don’t have a filter, you can leave a jug of tap water out overnight so chemicals like chlorine dissipate.

Light: the plant likes at least 5-7 hours of bright, indirect sun per day. Even with this much light, it is still a slow grower but it’s worth the wait.

Fertilizer: These houseplants don’t need a lot of fertilization. Fertilize about once a month with a standard houseplant fertilizer. Dilute the mixture by at least 50% to avoid burning the leaves.​

Care: Once every 3-4 years is about as often you should consider repotting them. When you do re-pot, be careful with the root systems. Unlike many plants, they need their root systems to be unharmed during re-potting or they may suffer for some time. Pick a pot that is three times larger than the size of the plant so the roots have time to spread and grow without worrying about root rot.​

Propagation: Benjamin fig is best propagated by cloning from cuttings. You will create a plant with the exact same genetics as the mother plant by propagating in this way. ​In the beginning of spring, take cuttings from your tree and place them in water for about a week or so. After a week, place cuttings directly in a soil made up of peat moss, perlite, and coarse sand.​ After 2-4 weeks, roots should be well-established. You can double-check this by gently tugging on them and seeing if they hold on to the soil.​

14.  Purple heart plant (Tradescantia pallida, syn Setcreasea purpurea)

This plant is the best air purifier among the species studied at the University of Georgia.

Also known as purple queen, purple heart, this is a striking plant with fuzzy, purple, lance-shaped leaves that reach lengths of 7 inches (18 cm). The stems grow straight up and then lean over, creating a cascading effect. Bright purple flowers appear at the end of the stems in summer and autumn. Purple heart works well in a patio container or hanging basket.

Soil: good quality, lightweight, commercial potting mix consisting of peat moss, perlite or compost

Water: water young purple hearts regularly, keeping the soil evenly moist until the plants are established and display new growth. Thereafter, water the plants only during periods of dry weather. Water generously to saturate the root zone as shallow watering creates shallow, weak roots. Don’t water again until the soil is dry.

Light: grow your plant in bright light year-round for good foliage color. It will grow in lower light, but the leaves will be more green than purple. Give it some direct sun, but shade it from noonday sun in summer to avoid scorching its leaves.

Fertilize: once every month while the plants are actively growing. Apply a general-purpose dry or liquid fertilizer according to the guidelines provided on the label. Always water immediately after applying fertilizer. Decrease feeding in the winter months, then resume when new growth appears in spring.

Propagation: take 4 in (10 cm) stem tip cuttings in spring or early summer. They’ll root easily in moist potting mix..

Care: Pinch off the tips of stems to to create a bushier plant. Repeat whenever the plants begin to look leggy or spindly. After flowering, cut the stems back to about half their height. Pruning the plants creates healthy, vibrant plants

15.  Bromeliad, Scarlet star (Guzmania lingulata)

This plant is the best air purifier among the species studied at the New York State University. Also, it is capable of releasing oxygen during the night, like the snake plant and the spider plant.

The bromeliad is a popular variety of plants that can grow outdoors or indoors when attached to another plant without causing the host plant harm, or in regular soil.

It takes three to four years to mature to the blooming stage, growing leathery leaves in stacking layers as they mature. The root system is small and forms above the soil. They produce a single stunning bloom in a cup-like fashion once in their life time. The bloom is hardy and lasts about five months. Within the center of the flower head small white flowers appear which are barely noticeable because they sit quite deep inside the head.

The flower head of this plant forms a wide, deep cup with multiple bracts coming out in layers. The coloration of these blooms begins as a deep green, which slowly fades into a yellow. By the time the bracts drape away from the main cup of the flower, they turn a deep, scarlet red (or orange). When viewed from above, the entire flower head takes on the shape of a star, giving the plant its name.

The leaves are long and umbrella out from the central stalk of the plant. They begin as a light green color with a soft feel, and mature into leathery, deep green leaves..

This plant is not toxic to cats and dogs.

Soil: this plant may be grown in two ways in nature. Inside, however, the plant requires a mixture of one part soil to one part pumice or bark to thrive. Drainage must be good at all stages of the plant’s life.

Light: this plant prefers bright, yet indirect, sunlight at all times. Too much sunlight will cause the leaves to sunburn and damage the flower.

Water: The roots should be misted on a daily basis. The soil must be watered to the point of wet, but never soggy. Once it has been watered, allow the soil to dry completely before watering again. Do not allow water to sit in the saucer underneath this plant. The cup of the flower must be kept filled with 1 to 2 inches of water at all times. Every four days, pour the old water out of the cup and provide new water. Never use anything except distilled or rain-sourced water, as the chemicals in processed water will kill the plant.

Fertilizer: this plant may be fertilized with a balanced fertilizer mix. This is to be diluted to half strength, and delivered directly to the flower cup as long as the flower is blooming. This should be done once a month. The fertilizer should be poured out after 4-5 days and replaced with regular water. Do not fertilize the root system. When the plant is not flowering, the leaves may be misted with the same fertilizer, diluted to one-quarter strength, once a month.

Propagation: a healthy plant will produce pups before it dies. Pups can be removed from the plant and transplanted to their own pot or they can be allowed to grow in clumps attached to the mother plant.

Care: throughout its life, the plant will occasionally have small shoots form near the base of the plant. These may be broken off at the root and propagated into new plants in separate containers once they reach three inches tall. This may be done even after the plant has bloomed.

16.  English ivy (Hedera helix)

This is one of top 10 house plants for clean indoor air in NASA Clean Air Study.

This plant is placed at the end due to its toxicity. You should exercise utmost precaution for your children, cats and dogs. Ensure nobody can touch the plant, and cats cannot jump at it. It’s best to let the plant drooping from the ceiling. Do not place it on the your table, writing desk, cupboard, bookshelf, or walkway… When you touch and prune it, ensure you wear gloves and eyeglasses, as the transparent but toxic plan resin can stick on your skin without your recognition.

This evergreen climbing plant is well adapted to indoor conditions. Different varieties will prefer different light situations, from bright, indirect light to low-light spaces. It’ll look especially picturesque growing from a hanging basket or around your windowsill.

Plant care: Water generously during growth, but don’t overwater during the winter.

Toxic to animals and humans: Although the English ivy thrives almost anywhere, it’s known to cause problems in dogs, farm animals, and humans when eaten. The chemicals in the sap can also cause severe contact dermatitis in humans, especially those with sensitive skin.

Picture: left CORRECT to hang high; right INCORRECT to put on bookshelf and furniture top.

Light: indirect light but not too dark and not direct sunlight. If your variegated ivy leaves turn green, that’s a sign that your plant needs brighter light to keep its variegation.

Water: keep the soil in your pot moist while your ivy plants are establishing themselves. After they’re mature, they can withstand drier periods and lower humidity. You’ll know you’re over watering when the leaves turn yellow and begin to droop.

Care: the plant does not like warm temperature. Avoid direct sunlight, the kitchen, or the warm draft near the hot component of your air conditioner.

Combined planting

The chart below summarizes air-purifying capacity of the plants in NASA Study.

You may combine several above-mentioned plants, each supplementing the others, in a miniature garden or a plant wall. It is advisable to engage a professional horticulturist to do the job for you, based on criteria such as:

• No toxic plants where they can be touched, or they should be at high.
• Ensure there is no excessaive himidity that may do harm to electronic appliances.
• Create a harmony between big and small plants, hanging plants and climbing plants…
• For a plant wall, arrange the pots so that they can be hidden by the foliage.

Some photos to give ideas follow.

 

 

 

 

 

 

Some basic principles for indoor plants

Watering. Overwatering is one of the most common causes of houseplant death. If you’re not sure how much to water, it’s better to err on the dry side than to give your plants too much moisture. All houseplants have slightly different watering requirements depending on how they are grown and changes in plant growth through the seasons. Therefore, it’s best to water on an as-needed basis rather than by a set calendar schedule. In general, plants grown in well-drained soil in an appropriate-size container should be watered when the top 1/2 to 1 inch of soil feels dry. Try where possible to use rain water, but if you can’t provide this, tap water is okay, just make sure its been allowed to sit at room temperature for an hour because cold water can shock the roots, and chlorine can be hazardous.

Fertilizing. It depends on plant’s growth rate and age, and the time of year. Avoid feeding houseplants when they’re not actively growing or if they are stressed. Most houseplants put on a growth spurt in spring and summer. This is the best time to fertilize them. During the short days of fall and winter, most houseplants need little, if any, fertilizer. Follow label directions to know how much plant food to use. Fertilizers come in a broad array of formulations, and it’s important to avoid overfertilizing your houseplants. Too much fertilizer can burn their roots and stunt their growth. For flowering varieties, use a fertilizer in which the three numbers on the label (nitrogen, phosphorus, and potassium, respectively) are relatively equal. If the nitrogen content is too high, the plant may grow a lot of leaves, but few flowers.

Grooming. Almost all houseplants look better with regular grooming. Dust collects on leaves, so wash them with a gentle shower of room-temperature water or dust them with a soft brush if the plants have hairy leaves. This improves the plant’s appearance and keeps the leaf pores unobstructed so that the plant gets more light.

Pruning and Pinching. The main reason for pruning houseplants is to make them look better. If one of your plants has a branch that’s too long, cut it back to a side shoot or main stem. Also remove any dead or diseased leaves and stems to help prevent the problem from spreading. Rejuvenate overgrown houseplants by cutting them back to 4 to 6 inches (10-15 cm) tall. This technique is effective in encouraging new growth for trailing plants such as Swedish ivy and pothos that may have become bare at their bases. Pinching means you remove stem tips, either with your fingernails or pruners. Pinch out the tip of a stem and the topmost leaves to promote growth of side buds. Plants that grow rapidly often look best with frequent pinching to keep them compact and bushy.

Trimming faded flowers. This is to keep the plant blooming and help prevent disease problems. While you’re at it, be sure to remove yellow, brown, or withered leaves. Use a narrow-blade hand pruner or sharp scissors to make a clean cut without tearing the plant’s stem.

Turning. For plants with a large foliage, tur the container 1/4 turn every week to maintain their natural look and symmetry.

Repotting. Not sure if your houseplants need repotting? Check the root systems. If the roots are circling the inside of the container, it may be time to repot the plant. If the plant has outgrown its pot you can transplant it into a slightly larger container. If you’d like to keep it in the same pot, trim off some of the roots with a sharp knife and replant it into the container using fresh potting soil. As you repot your houseplants, it’s also a good time to divide those with multiple stems to get new plants. Spring and summer are the best seasons for repotting your houseplants.

Insect Control. First thing first: isolate the infested plant from healthy ones. Second principle: do not use chemical insecticides indoor; do not replace toxic substances with others in your home! A forceful spray of water from the hose may knock down the population of the pests. Rubbing alcohol is effective on insects with waxy coatings such as scale and mealybugs. If you fail after several attempts, get rid of the infested plant. To continue you effot is to promote transmission of the infested to healthy plants.

Renting. If you can affort it, rent the plants. Grown and maintained by professionals, the plant will be more healthy and beautiful. You should set some conditions. First, chemicals must not be used, like for flowering or leave development; let the plants grow in their natural ways. Second, replace the infested plant with a healthy one. A sick plant is due to the renting company, so they should take responsibility. There are many renting companies that compete with each other, so this is your market!

References

• Wolverton, B.C.; Johnson, Anne & Bounds, K. (1989). Interior landscape plants for indoor air pollution abatement, Final Report, September 15, NASA.
• Ralph l. Orwell, Ronald l. Wood, Jane Tarran, Fraser Torpy & Margaret d. Burchett (2004). “Removal of benzene by the indoor plant/ substrate microcosm and implications for air quality”, Water, Air and Soil Pollution, 157: 193-207.
• Luz Claudio (2011). “Planting Healthier Indoor Air”, Environmental Health Perspectives, 119 (10): a426–a427.
• NASA Clean Air Study – https: //en.wikipedia.org/wiki/NASA_Clean_Air_Study
• 10 Best Air Filtering House Plants, According to NASA – https: //www.healthyandnaturalworld.com/best-air-filtering-house-plants/ NASA Study House Plants Clean Air – http: //www.zone10.com/nasa-study-house-plants-clean-air.html
• Planting Healthier Indoor Air – https: //ehp.niehs.nih.gov/119-a426/
• 9 Air-Cleaning Houseplants That Are Almost Impossible to Kill –https: //greatist.com/connect/houseplants-that-clean-air
• Your Latest Health Care Provider: A Plant – http: //healthland.time.com/2010/12/29/your-latest-health-care-provider-a-plant/
• Why Indoor Plants Make You Feel Better – https: //www.nbcnews.com/better/health/indoor-plants-can-instantly-boost-your-health-happiness-ncna781806
• Selecting the right house plant could improve indoor air – https: //www.acs.org/content/acs/en/pressroom/newsreleases/2016/august/selecting-the-right-house-plant-could-improve-indoor-air-animation.html
• Top 10 House Plants for Clean Indoor Air https: //www.thehealthyhomeeconomist.com/house-plants-for-clean-indoor-air/
• 5 health benefits of houseplants – https://www.treehugger.com/health/5-health-benefits-houseplants.html
• You Asked: Can Indoor Plants Really Purify the Air? – http: //time.com/5105027/indoor-plants-air-quality/

Compiled by: Diệp Minh Tâm