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Cosmos growing conditions


How to Grow and Care for Cosmos

Cosmos are freely flowering annuals that are easy to grow by sprinkling some seeds in the garden after any danger of frost has passed. These quintessential cottage garden flowers reach full maturity in about two months. Cosmos can be slower to germinate, but it blooms quickly after that and continues to flower through the fall. The flowers sit atop long slender stems and form a cloud of attractive color all summer that attracts bees, butterflies, and birds to your garden. Cosmos flowers look a lot like daisies. They come in a broad range of colors, with more cultivars developed every year. The leaves grow opposite on stems and are deeply lobed, pinnate, or bipinnate and feathery-looking depending on the type. If you plan to have cosmos and live in the southern U.S., consider keeping them as potted plants since they tend to be invasive there.

Common Name Cosmos, Mexican aster, cut-leaf cosmos
Botanical Name Cosmos sulphureus, Cosmos bipinnatus 
Family Asteraceae
Plant Type Annual
Mature Size 1-6 ft. tall, 1-3 ft. wide
Sun Exposure Full
Soil Type Well-draining soil
Soil pH 6.0–6.8 (Acidic)
Bloom Time Summer through fall
Flower Color Golden yellow, white, pink, magenta, orange, yellow, red, chocolate
Hardiness Zones 2–11 (USDA)
Native Area northern South America, Central America, and southern North America

Cosmos Care

Cosmos grow easily in beds and make great cut flowers. When established, the plants can handle drought, poor soil conditions, and general neglect. They even self-sow. This is a truly low-maintenance plant.

While some pests, like aphids, flea beetles, and thrips feed on cosmos, they're easy to control with a strong spray of water or insecticidal soap. Aster yellows, bacterial wilt, and powdery mildew may also affect cosmos. Space plants accordingly to ensure good airflow to avoid diseases.

Taller varieties look good in the middle or rear of the border with goat's beard, coneflowers, and black-eyed Susans. Shorter varieties make very colorful, airy edging plants.

Warning

Cosmos sulphureus is invasive in the southeast United States. Check with representatives from your local extension office to learn about any restrictions in your area.

​The Spruce / Letícia Almeida  Tim Bird / Getty Images  The Spruce / Letícia Almeida

Light

For the best flowering, choose a site that gets full sun. Cosmos will grow in partial shade but will have fewer blooms and be less vigorous when planted in shady areas. These plants will also thrive under uninterrupted full sun in the hottest conditions, much like their native habitat: the arid regions of Mexico and Central America.

Soil

Cosmos plants prefer a neutral soil with a pH of 6.0 to 8.0, although they will grow in poor soil where many flowering plants languish. They perform best in medium moisture, well-drained soils, but they will perform adequately in dry soils. Avoid planting in a rich soil; it can cause the plants to get too tall and flop over. You can prevent drooping by staking the plants or growing them close to other plants that can support them.

Water

Once established, you will not need to water your cosmos plants unless there is a prolonged drought. Where water is limited, these are the last plants that require irrigation.

Temperature and Humidity

Hot weather is ideal for cosmos, and they thrive in any humidity level.

Fertilizer

Fertilizing can negatively impact cosmos. Cosmos can handle poor soil. Too much fertilizer can often lead to strong plants with lots of foliage but few blooms. Unless your plants seem to be struggling, these plants do not need fertilizer.

Types of Cosmos

There are over 25 species of cosmos. However, three species are most commonly used in gardens and landscaping. Cosmos sulphureus is native to Mexico, Central America, and northern South America. With golden yellow blooms, it is very drought tolerant and loves hot weather. The plant grows 2 to 6 feet tall and comes in double and semi-double flowers. Some of the more recent cultivars tend to be shorter, more orangy, and with smaller flowers.

Cosmos bipinnatus are colorful daisy-like flowers that come in white, pinks, reds, and orange. At 1 to 4 feet in height, they are shorter than C. suphureus and are available in several popular hybrid series. Although they are not quite as heat tolerant as C. sulphureus, C. bipinnatus will grow well in just about any sunny space.

Chocolate cosmos are a separate species: Cosmos atrosanguineus. The dark red flowers smell like chocolate. This perennial is hardy to USDA zone 7, but it is higher maintenance than annual cosmos. Like dahlias, it grows from tubers.

Other common cosmos cultivars include:

The Spruce / Letícia Almeida Eva Lechner / Getty Images Suzanna Ruby / Getty Images

Pruning

The only real maintenance cosmos plants need is deadheading which will prolong the flowering season. If you fall behind, shear the plants by about one-third, when most flowers have faded. This kind of pruning produces a second flush of leaves and flowers. By the end of the season, you can cut off the plants at ground level or pull them up, roots and all. However, if you leave the plants in place, they may self-seed for the following growing season.

Propagating Cosmos

Cosmos plants readily self-seed. It's best to propagate these plants after the threat of frost is gone. Although sowing seeds is the best and easiest way to propagate this plant, you can also propagate via stem cutting. When you take stem trimmings, it stimulates more leaf and flower growth. Besides seed, stem cutting is the best way to propagate this plant. Here's how you do it:

  1. You'll need sterile pruning shears or scissors and a pot of sterile, well-draining potting soil.
  2. Fill a small 3-inch container with moistened potting soil. Using a pencil tip, push straight down in the soil about 1 to 2 inches deep, making a shallow hole.
  3. Look for a cosmos shoot that has 3 to 5 leaf nodes on the stem. Cut under the last leaf node. At the last leaf node, carefully cut off the leaves, leaving the node intact for new growth.
  4. Bury the cut tip of the stem in the pencil-made hole. Make sure that the last leaf node is above the soil line. Push down the soil around the stem, compacting the soil to keep the stem upright and in place.
  5. Water generously and keep moist. You should notice new leaf growth within three weeks. If you do, you can gently pull the root ball out of the container, Transplant the root ball to its new location.

How to Grow Cosmos From Seeds

Start seeds indoors, four to six weeks before the last frost. Or if you can sow cosmos outdoors directly in the garden well after the threat of frost is gone. Cosmos grow very quickly but can be killed by a late frost, so don't rush it. They typically germinate in 7 to 21 days at 75 degrees Fahrenheit, followed by flowering in about 50 to 60 days.

Loosen the soil to a depth of 8 inches. Plant the seeds and cover them with 1/4 inch of fine soil. Seed packets usually recommend precise spacing, such as at 2-foot intervals, or you can scatter the seeds and let the plants support each other as they grow. You can always thin them out later, moving the extra plants to another part of the garden.

Potting and Repotting Cosmos

When growing cosmos in pots, make sure the container has bottom drainage holes. Cosmos can't handle overly wet, soggy soil. Plan on growing one cosmos plant per gallon of your container. If growing in pots, do not enrich the soil, it makes the plants grow tall, leggy, and droopy. Also, tall varieties will need staking in containers. At the very least, plan on using at least a heavy, 12-inch diameter container.

Overwintering

Cosmos is an annual. If left outside in frosty temperatures, they will die. However, at the end of the growing season, if you allow the dead flower heads to drop their seeds, cosmos seeds will go dormant and sprout when the soil warms up again in the spring.

If you have a potted cosmos in a container and want to keep your cosmos alive over the winter season, you will need a bright full sun growing lamp for at least 7 hours a day. You will need to snip off any blooms as they form. This plant's life cycle ends with flowering when it drops its seeds for the next growing season.

How to Get Cosmos to Bloom

Cosmos plants need full sun to bloom. Even the hint of shade, can restrict flowering. Also, to encourage more blooms, you need to deadhead the old blooms. For faster blooms, prune between the main stem and a leaf. The lower you cut in the stem, the longer it takes to grow more flowers.

Common Problems With Cosmos

Cosmos are easy to grow and maintain over the growing season. They are usually resistant to disease, and most insects; however, some pests can become a nuisance and affect their growth.

Wilting or Leaf Discoloration

If your plant has ample water and is not wilting from a lack of hydration, there are two possible causes.

A plant that is wilting with leaf discoloration might have a common fusarium fungal infection. If you dig up the plant and notice a pink mass on the roots, then the plant likely has fusarium. The whole plant is beyond help, will die, and should be disposed of to stop the fungus spread.

If you dig up the roots and they look healthy, the plant may have a bacterial wilt infection. The bacteria cause the stems to wilt at their base. This plant will die and should be disposed of.

Yellowing Leaves and Leaf Drop

Powdery mildew mainly affects plants in the shade. Fungus spores fly through the air and attach to a host plant in a shady spot. It creates a powdery white coating on leaves and causes leaves to yellow and fall off. To prevent powdery mildew, provide your plants good circulation, bright light, and avoid getting water on the leaves. If your plant has fungus, use a horticultural fungicide according to the package instructions.

Flowers Distorting or Stunting in Growth

As a member of the aster family, cosmos can get aster yellows, a disease spread by leafhoppers (a tiny grasshopper-looking insect). The leaves will get yellow mottling on the leaves, and the flowers will appear distorted or stunted. Dispose of these plants since there is nothing you can do help them recover.

FAQ

Article Sources

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Cosmos sulphureus Cav.sulphur cosmos. United States Department of Agriculture.

  2. Cosmos (Cosmos). Connecticut State Agricultural Experiment Station.

  3. Cosmos bipinnatus. Missouri Botanical Garden.

  4. Fusarium Wilts. Royal Horticulture Society.

  5. Diseases of Cosmos. National Gardening Association.

  6. Powdery Mildew. University of California Integrated Pest Management.

  7. Cosmos: Aster Yellows. University of Minnesota Extension.

expert tips on when and where to plant |

(Image credit: Unsplash Mathew Schwartz)

Garden favorites for summer color, learn how to grow cosmos and you can enjoy clouds of these daisy-like flowers dancing in the breeze and filling garden beds and borders.

Ranging from pale pastels and whites through to bright pinks, crimson, orange and other zingy colors, these annuals are enduring favorites for flower bed ideas. They will happily self seed for several years, filling your yards with their open-faced blooms that can go on for months and months, adding to your palette of late summer flowers and still displaying their cheery blooms until the first frosts of fall.

Cosmos comes from the Greek ‘kosmos’, meaning beautiful, and growing tall with their fine, feathery deciduous foliage, cosmos are definitely one to include if you're planning a cut flower garden as the more flowers you pick, the more you'll get.

There are many cultivars available, including doubles, others with tubular rays and some bi-colors, in different tall and compact varieties.

Once you know how to grow cosmos you'll be using them to brighten up all corners of your garden.

How to grow cosmos from seed

(Image credit: Getty Images)

It is easy to get to grips with how to grow cosmos from seed and they can be sown any time throughout spring depending on the hardiness zone where you live. The seeds are large, long and thin, so easy to handle and germinate quickly.

'Cosmos are the very best, low-maintenance and floweriest plants in the world. With little effort, they give you buckets of cut flowers and they have a good vase life, too. Easy to grow, long-flowering and brilliant for picking, it’s hard to fault them,' says expert plantswoman, Sarah Raven .

These pollen-rich flowers are also an excellent lure for bees and other pollinators to attract them into a wildlife garden. 'They are stacked with nectar and pollen, so bees and butterflies love them,' agrees Sarah. too. 

Cosmos bipinnatus, the most commonly grown, also known as Mexican aster, originates from the Americas.

When it comes to growing cosmos from seed you have two options. You can grow them in modules or seed trays indoors, or plant them directly out in the garden. There are benefits to both. 

(Image credit: Future/Leigh Clapp)

How do you successfully grow cosmos?

Growing cosmos in modules or seed trays indoors to start them off, gives you more control over the blooms. Keeping them off the ground and under cover will also protect the delicate seedlings from slugs and harsh weather. Plus, since you are starting your plants off indoors, you are able to start planting earlier – in early spring – so will have well established flowers that attract bees by early summer. 

Sow indoors in module or seed trays, covered with about 2mm of good, fresh compost. Water from below, allow excess water to drain away and position in a warm place, ideally 60 to 70 0°F (16 to 21°C), to germinate, which takes around 30 days.

Move seedlings to a cold frame or light, sheltered spot for a few weeks before planting out to harden them off. This will result in 'much faster growing and longer-lasting flowers,' says gardening guru Monty Don on his blog . He also recommends doing the same for young cosmos that are bought in the garden center, too. 

Direct sowing cosmos outdoors

(Image credit: Leigh Clapp)

If you choose to direct sow cosmos outdoors, this is a low-maintenance choice that is beautiful for a cottage garden idea. 'I place them in groups so they make drifts and clumps rather than straight lines,' says Monty.

For how to grow cosmos seeds outdoors, wait until the soil has warmed up, then:

(Image credit: Getty Images)

Where do cosmos grow best?

Cosmos grow best in a sunny spot, protected from wind, with well-drained, light soil. It is advisable to mulch the ground to conserve moisture, and if you learn how to make leaf mulch you can use your own organic garden material.

If you live in a very warm zone that can suffer extreme heat, cosmos will tolerate part shade.

Cosmos tolerate most pH levels, but do best in neutral to alkaline soils and are quite drought tolerant, so might be worth adding to your planting palette if you're planning a dry garden. Long periods or wet and cold are detrimental and can delay flowering.

Plant your cosmos in a group to make a real focal point statement for late summer into fall until the first frost. This will also attract more bees than if they are dotted through the garden. 

Cosmos are useful for cheery color in any area of a backyard and suit a range of styles – from planting a cottage garden border, creating a prairie style naturalistic planting design, or planting a wildflower meadow.

‘I love to grow lots of different varieties of cosmos, putting together different heights and colors in pots and for borders for wonderful layers of intense colour,’ says Sarah Raven.

They are also excellent for companion planting alongside vegetable and fruit crops in a kitchen garden, as they entice pest predators and valuable pollinators. 'We plant cosmos with our vegetables, in rows to help support each other,' explain Henrietta Courtauld and Bridget Elworthy, the Land Gardeners .

When to plant cosmos seeds

(Image credit: Leigh Clapp)

Early spring is the best time to sow cosmos seeds under cover indoors, which will then produce flowers that bloom earlier in summer.

Alternatively you can direct sow cosmos seeds in their flowering position once the soil has warmed up. This will differ depending on the area where you live, but will be from about late May in cooler regions, and earlier in warmer zones.

Bought seedlings can be planted in late May or June.

Is cosmos easy to grow?

Yes cosmos are easy to grow. 'Cosmos is one of the easiest flowers to grow from seed that is directly sown in the garden bed,' advise the experts at American Meadows .

‘As they grow, stake cosmos if necessary, and water them regularly,' says Sarah Raven.

Cosmos suffer from few pest problems. Watch out for slugs and snails, though, especially when the plants are young and tender, so use slug barriers. To avoid powdery mildew and fungal diseases ensure your plants have space and the soil isn’t soggy. 'Cosmos prefer dry, arid soil over wet conditions. Soil that is too moist may lead to disease,' advise the American Meadows experts.

(Image credit: sarahraven. com / Jonathan Buckley)

Can you put cosmos in pots?

Cosmos, particularly the shorter varieties, can be grown in pots, and make attractive patio and container plants. As they are good at attracting beneficial insects to veg and fruit crops, why not include them in your vegetable garden container ideas? 

Try a mix of shorter dwarf cosmos varieties, such as the Sensation and Sonata mixes, grown from seed, or buy as seedlings and plant out from May, spaced about 11in (30cm) apart. Cosmos work particularly well in pots with zinnias.

Use a light potting mix, in pots with good drainage and place in a sunny spot. Water regularly and feed with a liquid fertilizer every few weeks during summer. 

(Image credit: Leigh Clapp)

How to keep cosmos flowering

If your cosmos aren't flowering, you could be making one crucial mistake. An important step in how to grow cosmos and keep them flowering is to deadhead the blooms. This stops the plant putting its energy into creating seeds and instead puts its efforts into creating more flowers.  

Chances are you will be busy in the garden deadheading roses and petunias, and other blooms, so add cosmos to the list.

'As long as you don’t cut the plants right to the ground, but above a pair of leaves, more buds will form to fill next week’s vases and more for the week after that. The lower you go in the plant, the more delay between the flower you've just picked and the next flower,' explains Sarah Raven. 

'We love cosmos because it is light and airy and has the joy of endless giving – every time you deadhead another flower appears,' add the Land Gardeners.

(Image credit: Thompson & Morgan)

Do cosmos come back every year?

Nearly all cosmos are annuals meaning they do not come back every year. In order to have blooms every year, you will need to resow the seeds the following spring. 

The only exception to this rule is chocolate cosmos, cosmos atrosanguineus, which is grown like a dahlia from a tuber and is a perennial. Chocolate cosmos is loved for its delicious vanillary-chocolate scent and velvety brown flowers, and since it is a perennial, will come back year after year. 

Annual cosmos can also self seed. If you let some of your cosmos flowers die naturally and fall to the ground they will germinate seeds by themselves. Allowing plants to self seed is a step on the way to creating an eco-friendly garden.

You may also like to try collecting seeds to save from the flowers to sow next spring. If you want to save seeds be aware that hybrids will not grow true-to-type, so select varieties that have been open pollinated, as opposed to hybrids – which can vary widely in the next generation.

You can collect cosmos seeds at the same time as you are collecting zinnia seeds and those of other flowers that you love. This is a cost-effective way to populate your garden with flowers, year on year.

Scatter the collected seeds in your garden or save in labelled envelopes or paper bags for sowing the next year.  

(Image credit: Leigh Clapp)

Do you pinch cosmos?

You should pinch out the growing tips of cosmos to encourage branching and flowering, and in around 12 weeks you should see your first blooms.

If you then want to enjoy those flowers in the house as well as in the garden, cosmos make excellent cut flowers. To harvest for cut flowers, cut the cosmos blooms when they are beginning to unfurl in the morning, as this is when there will be the most moisture making them less likely to wilt.

Plunge the blooms into a bucket of warm water, stripping off lower leaves to avoid them in the water. There are many tricks for how to keep flowers fresh in a vase. Re-cut the stems regularly and refresh the water and cosmos should last up to 10 days in the vase. 

(Image credit: Pippa Blenkinsop)

Do cosmos need staking?

The taller varieties of cosmos will need staking to prevent them flopping over.

They can grow up to 8 feet (2.5m) and flowers can reach 3 inches (8cm) across.

‘It’s worth taking the time to stake them properly as they benefit greatly from growing straight early on. If they collapse, they’ll never grow or flower as well as when vertically supported,’ explains Sarah Raven.

How often should I water cosmos?

Water cosmos regularly until they are established, or during dry spells. It is important, however, that you do not over-water cosmos as this can result in plants with fewer flowers. 

Cosmos can tolerate dry soil, even in a hot, sunbaked spot. In fact, they prefer poor soil and seem to thrive on a bit of neglect!

(Image credit: Leigh Clapp)

Do cosmos like sun or shade?

Cosmos are sun loving flowers, although they will tolerate a little shade in warmer climates.

Cosmos and zinnias are good companions and mix them also with other sun-loving plants in borders, beds, meadow planting and containers, such as Verbena bonariensis, alstroemeria, calendula, eryngium, dahlias and nepeta.  

'Cosmos can be combined with almost all full sun border plants to give that "wow" factor mid to late season. Infilled in a shrub border or alongside flowering plants, such as monarda, salvias and gaura works well,' says garden designer Charlie Bloom. 

The range of colors allows for diverse combinations, whether bright and breezy or more subtle, so there’s lots of scope.

Rachel is senior content editor, and writes and commissions gardening content for homesandgardens.com, Homes & Gardens magazine, and its sister titles Period Living Magazine and Country Homes & Interiors. She has written for lifestyle magazines for many years, with a particular focus on gardening, historic houses and arts and crafts, but started out her journalism career in BBC radio, where she enjoyed reporting on and writing programme scripts for all manner of stories. Rachel then moved into regional lifestyle magazines, where the topics she wrote about, and people she interviewed, were as varied and eclectic as they were on radio. Always harboring a passion for homes and gardens, she jumped at the opportunity to work on The English Home and The English Garden magazines for a number of years, before joining the Period Living team, then the wider Homes & Gardens team, specializing in gardens.

how and why to grow fresh vegetables in space — Knife

Why do astronauts need vegetables and fruits?

We remember from childhood that "an onion cures seven ailments", and "an apple for dinner - and a doctor is not needed", in other words, fruits, vegetables and greens are the basis of a healthy diet and a source of vital substances. The World Health Organization advises adults to eat about 400 grams of fruits and vegetables every day. Of course, there are vegetables in the canned food of astronauts, but it cannot be compared with fresh crispy fruits on Earth. Vegetables and fruits are sent to the ISS with each cargo ship, but parcels from Earth are not enough for a short time.

In addition, over time, frozen packaged food just gets boring.

Cosmonaut Anton Shkaplerov says: “The diet is very varied… But of course, all this is not fresh: either canned or reconstituted. After a month or two, it all becomes boring and you really don’t want to eat anything, there is no appetite as such ... eat simply because you need to eat.

It's not just sad - astronauts often lose weight due to lack of appetite, says Norwegian biologist Silje Wolf. These problems can be largely solved by own beds on board.

Space gardens are also good for the psyche of astronauts. They have plenty of sources of constant stress: high risk, non-standard situations at work, and even the closed space of the station, where it is difficult to be alone for a while. Gardening is known to help reduce symptoms of depression and anxiety, as well as improve subjective feelings of well-being. Scientists from the University of Florida collected the testimonies of Soviet and American cosmonauts and came to the conclusion that this also works under the conditions of orbital stations. For example, American Peggy Whitson, who conducted an experiment with soybeans on the ISS, was amazed by her own reaction to sprouts in the onboard greenhouse: “I think the opportunity to see something green for the first time in a month and a half on the station made a really strong impression on me.”

Astronaut Don Pettit was so impressed by his work with plants that he published an entire diary on his blog from the point of view of an orbiting zucchini: "Nothing compares to the smell of living green in this forest of engineering machines."

Today, space farming technologies are being developed for stations in Earth orbit, but biologists have other goals that are much more ambitious. Researchers and enthusiasts are increasingly talking about the colonization of other planets. Specific figures appear in plans and projects: how long the flight will last and how many people will be able to become the first colonists. The road, for example, to Mars will take many months, and even longer people will have to settle in a new colony. According to NASA ISS program expert Julie Robinson, even the most modern preservation and freezing technologies will not allow all the necessary nutrients to be stored in the food of immigrants for so long.

A new settlement cannot survive on canned food alone, relying on supplies from Earth is risky, so we need methods that will allow us to grow plants on our own. They will have to be tested in the harshest conditions - after all, on the same Mars, the colonists are waiting for dust instead of fertile soil and harsh ultraviolet light instead of gentle sunlight filtered by the earth's atmosphere.

Why is gardening in space so difficult?

Mankind made the first steps towards space plantations at the beginning of 1980s, when the astronauts of the Salyut-7 station managed to get the seeds of Tal's resicum. This small plant from the cabbage family has become for plant researchers what the Drosophila fruit fly is for animal biology: the full development cycle of Tal's clover can take as little as 6 weeks. Since then, many crops have been grown in orbit, from lettuce to wheat, but these crops, at best, become a pleasant addition to food: it will not be possible to fully provide the inhabitants of space stations with vegetables for a long time.

What exactly prevents the creation and cultivation of "six acres" outside the Earth? The authors of the Botany Letters review article cite several reasons. The most obvious of these is microgravity : both in Earth orbit and on potential colony planets, gravity is less than we are used to. Weak gravity affects many features of the development of organisms, and plants are no exception. In experiments where the same crops were planted on Earth and on the ISS, some species in orbit noticeably lost their taste and nutritional value. For example, in the "cosmic" embryos of the turnip Brassica rapa, there was much less starch and protein (by 24%). The air temperature, humidity and light levels around the plants at the station were almost the same as on Earth, so scientists believe that low gravity is to blame. Perhaps the fact is that in zero gravity, plants begin to "suffocate": water in such conditions envelops the roots in a thicker layer, causing oxygen starvation.

At closed stations there is another problem - violations of convection (heat exchange) that occur if the enclosed space is poorly ventilated. At the same time, volatile organic substances accumulate around the plant, which can slow down its growth.

Do not forget about radiation . Observations show that constant radiation can cause DNA damage and mutations, and also affects the level of gene expression [the way hereditary information from genes is converted into RNA or protein. - Approx. ed.]. Given all this, it is impossible to predict how plants brought from Earth will change over time. Experiments with radiation have already made Tal's roots, stems and leaves "lose weight".

When it comes to vegetable gardens on space stations, scientists are rather optimistic: most of these problems can be solved by studying what conditions plants need and which species best tolerate the absence of their usual environment.

It will be more difficult for future colonists of other planets, because the "soil" of new worlds can bring many unpleasant surprises.

Our terrestrial soil, which gives life to plants, is a complex system where both minerals and organics are equally important. On Mars, for example, the situation is quite different. The surface of the Red Planet is covered in regolith, fine sand and dust that forms when rocks are eroded by wind, temperature fluctuations, and meteorite impacts. This dust is not only lifeless, it is dangerous for plants: it contains toxic compounds, including Perchlorates Perchloric acid salts.

Chinese scientists have found how a similar concentration of perchlorates in water affects several types of plants: toxins noticeably reduced both stems and roots. In addition, perchlorates accumulated in the leaves, so it would not be possible to include such plants in the diet. And salts of perchloric acid will not allow the surface of Mars to be populated with terrestrial bacteria in order to create a fertile layer of humus. The experiments of Scottish astrobiologists have shown that perchlorates enhance the germicidal effect of ultraviolet radiation, so our soil bacteria simply cannot survive on the surface of Mars.

It is possible that the idea of ​​vegetable gardens on the Martian regolith will have to be abandoned altogether, focusing on other methods - primarily hydroponics and aeroponics technologies.

Soil substitutes

Today's space gardening practices can be broadly divided into those that require a relatively dense substrate (say, soil or clay) and those that rely on water and liquid solutions.

The Vegetable Production System (Veggie), which has been supplying the ISS with fresh herbs since 2014, is closer to the first type.

In Veggie, the seeds germinate in special pads where calcined clay is mixed with fertilizer capsules. The polymer shell of the capsules is gradually destroyed, releasing the next portion of top dressing in time. The structure is illuminated by green, red and blue LEDs - during the experiments, the astronauts periodically change the lighting mode to find out what works best for certain plants. The facility has an automatic watering system using capillaries, but sometimes the astronauts water the orbital garden themselves. For example, Scott Kelly had to do this to save zinnia flowers from an unexpected drought.

When the Veggie has served its end, it is planned to be replaced by a larger unit - the fully automatic "greenhouse" Advanced Plant Habitat (APH). It will be possible to adjust many parameters, including humidity, pressure, light, the amount of oxygen and nutrients supplied, and even measure the temperature of individual leaves. NASA loves speaking abbreviations, so the system for monitoring many parameters was called PHARMER (Plant Habitat Avionics Real-Time Manager in Express Rack). Researchers at the Kennedy Space Center have already thought about the first experiments involving APH.

Researchers intend to bring seeds matured on the ISS to Earth, germinate them in the laboratory, and return a new generation of seeds to the station to find out how such strong gravity drops will affect them.

Cosmonauts of the Russian segment of the ISS have also carried out many experiments. From 2002 to 2011, two varieties of barley, radish, "Japanese cabbage" mizuna, dwarf wheat and dwarf peas were grown in the Lada automatic greenhouse. These experiments showed that many of the most important functions of plants, such as fertilization and the formation of embryos, do not change in space.

A few years ago, the Institute of Biomedical Problems (IMBP) of the Russian Academy of Sciences created a new greenhouse "Lada-2", in which they planned to grow wheat, lettuce and sweet peppers. Unfortunately, Lada-2 died in the accident of the Progress MS-04 cargo ship in 2016. There are no plans to create a new greenhouse to replace the lost one at IBMP: the process will take several years, by which time the ISS operation cycle may come to an end. Now Russian cosmonauts are conducting experiments on the equipment of the American segment of the station. Perhaps in the future, another Russian development will go into space, the Vitacycle-T greenhouse with a rotating cylinder inside.

Just add water: hydro and aeroponics

The need to use soil or clay for "beds" is rather a drawback in space travel conditions. Solid substrate weighs a lot, the capacity of cargo ships and compartments is always limited, moreover, earth particles can get into the ventilation at the station, and suitable soil cannot be found on future colony planets. Therefore, researchers are increasingly looking towards methods in which greens and vegetables grow in water - hydroponics and aeroponics.

"Garden" in a liquid solution rich in nutrients is not a new idea; Francis Bacon wrote about this method in the early 17th century. Since then, many soilless gardening techniques have emerged, giving space tech makers a lot to choose from. For example, you can keep the roots in the water all the time or use the ebb and flow technique, as well as use a variety of substrates that retain the right amount of liquid.

Aeroponics may turn out to be even more promising: in this case, the roots of plants are not in water or substrate, but in the air. Sprayers are installed nearby, which from time to time envelop the roots with a light haze from tiny drops of nutrient solution. In this way, plants receive both nutrition and a sufficient amount of oxygen - the risk of suffocating the crop with a layer of water is much lower than in the case of classical hydroponics. The risk of plant disease is also reduced, as dangerous microorganisms often settle in water or wet substrate.

Hydroponics and aeroponics have long been successfully used on Earth. They allow you to harvest even in extreme conditions - for example, in Antarctica.

Scientists from the German Institute for Polar and Marine Research. Alfred Wegener has been growing cucumbers, tomatoes, sweet peppers and herbs for several years at the Neumayer-Station III Antarctic station.

The aeroponic greenhouse was set up in a separate building, and when a snowstorm prevents scientists from getting there from the main building, their colleagues from Germany can remotely control irrigation and lighting. Biologists say that one of the main tasks of their work is to prepare new gardening methods for testing in space conditions.

Another find for closed life support systems is anthroponics , when crew waste is used as a source of water and fertilizer for hydroponic installations. For example, the urine of astronauts can become the basis of nitrogen fertilizers, Italian scientists have already conducted such an experiment on Earth. It all looks like the famous scene from The Martian, but in reality, switching to this technology is not so easy. Excrement of astronauts may contain, for example, an excess of certain metals, so following the example of Mark Watney will succeed (or, conversely, fail) only after much research.

Like on a volcano: experiments with regolith analogues

Despite the prospects of hydroponics, there are also supporters of gardening based on the soil of other planets among scientists. Such experiments have been going on in the Netherlands since 2013. Biologists from Wageningen University grow vegetables in artificial soil, which most closely resembles the composition of regolith from the surface of Mars and the Moon. "Martian" soil is made from volcanic ash and sand from Hawaii, and "lunar" soil is made from desert sand in Arizona. To repeat the texture of regolith, the material is additionally crushed into dust.

Scientists have already harvested more than a dozen crops, in their food basket are tomatoes, peas, radishes, rye, green onions and other plants. The first tests showed that the level of toxic heavy metals in vegetables does not exceed the permissible limits (however, new crops will still be tested many times).

In 2017, worms were placed in a Martian soil sample, and they not only survived, but also gave birth.

Project manager Wiger Vamelink says that earthworms can become an important part of agriculture on other planets: they enrich the soil with vermicompost, and their passages help water and air to better penetrate into the soil.

Of course, Vamelink's forecasts are very optimistic. The conditions on the Red Planet are harsh: plants will not only have to survive in dusty soil, but also resist the onslaught of ultraviolet radiation - the level of radiation on Mars is much higher than on Earth, since our planet is protected by the ozone layer. Do not forget about toxic perchlorates: it is not known whether there is a way to clean the soil and how much it will cost. However, even if planting gardens on Mars using the Vamelink method does not work, the results of his work will be useful on Earth - for example, they will help identify plants that produce a stable crop on volcanic soils.

New Earth: Terraforming Projects for Other Planets

Each of these experiments is a small step towards the future of space gardening, but there are some scientists who think big. Proponents of the idea of ​​terraforming propose not to be limited to small vegetable gardens and greenhouses: they intend to create from scratch on any other planet conditions suitable for the life of terrestrial plants and animals. The problem is that finding a second Earth is not easy: you will have to start not even from scratch, but from a serious “minus”.

The most popular candidate for Earth 2.0 is, of course, Mars. It is located not far from us by space standards, has reserves of water ice and an atmosphere - very rarefied, but still capable of protecting at least a little from radiation. Terraforming projects mostly focus on thickening the atmosphere. For example, the group of Jim Green, Director of NASA's Planetary Science Division, proposed surrounding the Red Planet with a shell of an artificial magnetic field. According to Green's plan, it will be created by a spacecraft located at the Lagrange point L1 between the Sun and Mars. How exactly this device should work, the astrophysicist did not specify.

According to Green, the magnetic shield will "melt" the frozen carbon dioxide in the ice caps at the poles of Mars, this will start a greenhouse effect, and the temperature on the planet could rise by several degrees. This is enough to melt some of the water ice, as well as gradually raise atmospheric pressure, bringing Mars closer to Earth conditions. However, in 2018, NASA experts said that it would not be possible to “warm up” Mars with the help of CO 2 - at least with the current level of technology. According to Bruce Jakoski and Christopher Edwards, there is not enough carbon dioxide on Mars to implement such projects.

Another bold idea is to change the Martian atmosphere with the help of cyanobacteria (blue-green algae). These small organisms are capable of photosynthesis: it is believed that they "breathed" a significant part of the oxygen that contributed to the "oxygen revolution" at the beginning of the Proterozoic. In 2018, an international team of scientists found that cyanobacteria can produce gas in very low light levels.

Blue-green algae can withstand very harsh conditions, some of them are extremophiles - perhaps some of them will survive on Mars.

For now, terraforming remains more of a dream than a concrete strategy. But the authors of these concepts agree: Earth technologies are developing rapidly, and decades later we will be able to talk about the development of other planets much more specifically. Who knows, suddenly the Martian apple trees will become a reality?

Growing plants in space