How to Grow Mexican Aster: Cosmos Bipinnatus

Today we will learn to Grow Mexican Aster Plants. It is a wild annual flower from the Asteraceae family. It is a type of aster with similar flowers yet different plant structures. Mexican Aster plant is light green. The stems are soft and delicate. It has thin soft needle-like leaves. These thread-like leaves of Mexican Aster give it a unique charm. The bright vibrant flowers and unique leaf structure make this a must-have for every garden owner.

The Botanical name of Mexican Aster is “Cosmos Bipinnatus”. This name resembles the genus Cosmos and Species Bipinnatus. The term Bipinnatus is given to the Cut leaf structure of these plants. Mexican Aster is native to Mexico. It can grow in any Hardiness zone from 1 to 10. This means you can grow these beautiful flowers anywhere you want. Mexican Aster is ideal for cut flowers and attracts Butterflies. So if you want to know more about these plants then keep reading keep gardening.

How to Grow Mexican Aster: Cosmos Bipinnatus?
How to Grow Mexican Aster: Cosmos bipinnatus CC By: 4.0

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Mexican Aster plant Info

Botanical Details of Mexican Aster

  • Common Name: Mexican Aster, Cut Leaf Cosmos
  • Botanical Name: Cosmos Bipinnatue
  • Genus: Cosmos
  • Species: Bipinnatus
  • Family: Asteraceae
  • Origin: Mexico
  • Hardiness Zone: USDA Agricultural zone 2 to 10. You can grow Mexican Aster in Zone 1 during the peak summer season.
  • Plant type: Annual Herbaceous Flowering plant.
  • Plant Structure: Soft stem structure. Mexican Aster can grow 2 to 5 or even 6 feet in length and spread up to 3 feet wide. Plant size can vary a lot with different varieties of Mexican Aster along with growing conditions.
  • Bloom Time: Mexican Aster can bloom from fall through summer according to local climatic conditions. Bloom time differs in different Agricultural hardiness zones.
  • Flower: Small 2 -3 inch flower comes in a variety of colors. The most popular color variations in Mexican Aster are Pink, Purple, Violet, red, yellow, and white. Some hybrid Mexican Aster can have blooms with multiple color tones.
  • Foliage: Fine light to medium green leaves and stems.

Growth Conditions for Mexican Aster

  • Soil Requirement: Mexican Aster requires Soft moist soil with good drainage. It prefers semi-dry nutritious soil better than damp humus.
  • Soil Ph: The soil must have a consistent slightly acid to basic soil ph in the range of 6.0 to 7.6.
  • Temperature: 55 to 70 degrees Fahrenheit is ideal for Mexican Aster. You should wait for the risk of frost to over before moving them outside in the garden.
  • Sunlight: Mexican Aster plants need 6 to 8 hours of direct sunlight to properly bloom. Although they can easily survive in Part shade.
  • Water: Mexican Aster plants require a minimum of 1-inch water per week. Always keep the soil moist to 2 to 5 inches of soil depth. Underwatering or overwatering both can reduce flowering in Mexican Aster.
  • Propagation: You can grow Mexican Aster from seeds as well as cutting. Although gardeners prefer seed over cutting as it is an annual flowering plant. You will need extra time and a parent Mexican Aster plant to grow a healthy cutting.
  • Plantation Time: November to February in Zone 9 through 11. February to Late April in zones 6 through 9. In zones, 1 to 5 grow Mexican Aster in May through August.

Uses & Speciality of Mexican Aster

Mexican Aster flowers are good to use as Cut flowers. They can easily last for 2 to 3 weeks with proper care. This wildflower is ideal to decorate garden edges and borders around flower beds.

Mexican Aster not only adds color to the garden but also attracts natural pollinators like Bees and butterflies. Therefore, Grow Mexican Aster in your garden and keep your garden healthy and colorful.

Soil Requirements for Mexican Aster

Mexican Aster plants need soft soil with good drainage. The soil should have a balanced neutral ph in the range of 6.0 to 7.6. You can amend the soil with compost, lime, or wood ash to adjust the ph levels.

If you are planning for container gardening then make sure the soil is extra light and the container must have a bottom drainage hole.

Mexican Aster is a wildflower so it can thrive in a variety of soil types and conditions. You can easily grow these flowers in flat garden beds or rock gardens. A little bit of moisture and nutrition is sufficient for these plants.

Although I prefer using compost with garden soil and sand to grow Cosmos Bipinnatus: the Mexican Aster. The compost helps in maintaining nutrition for a long duration. It also retains enough moisture to keep the roots hydrated even during dry spells. Sand helps with the drainage. It makes the soil porous and granular instead of smooth and fine like clay. This helps the water and nutrition to reach the root system without logging.

You can amend the Garden beds with 3 to 5 inches of compost, leaf mold, and a little bit of fungicide a week before sowing Meican Aster seeds. It will keep the soil nourished and well hydrated for 3 to 5 months.

Where to Grow Mexican Aster?

Mexican Aster plants are native to Mexico. These wildflowers can grow anywhere from Hardiness Zone 1 through 10. So location is not a big problem. It only requires well-drained nutritious soil.

The preference of the growing location for Mexican Aster is your personal choice. Though it better fits in garden edge and border covers.

Keep in mind Mexican aster is a self-seeding plant. It means wherever you grow them once, they will come back every year. Therefore, make sure the choice of location is perfect for the continuous growth of These beautiful wildflowers. It must not interfere with other garden flower and vegetable plants.

They are ideal flowering plants to grow in coastal regions to the piedmont and mountains. This versatile nature of Mexican Aster plants makes it ideal for every backyard gardener.

When is the right time to Grow Mexican Aster?

Mexican Aster is moderate to warm weather flower. It prefers the spring season to grow and bloom. Although the right growing season may vary with your local hardiness zone.

The right time to plant Mexican Aster in Zone 7 is in May & June. Gardeners in Zone 8 can start in April and May whereas in Zone 9 the month of March and April or September and October is ideal for Mexican Aster. Grow Mexican Aster in Zone 10 and 11 from November to February.

The right time for the Mexican Aster plant is when the night temperature exceeds 50 degrees Fahrenheit. Else wait for the risk of frost to over and then plant your Mexican asters in the garden.

Can we Grow Cosmos Bipinnatus Indoors?

Yes, you can grow Cosmos Bipinnatus indoors. Any member of the Cosmos genus including Mexican aster can survive well in part shade. It requires 6 to 8 hours of direct sunlight through it can bloom even with 4 hours.

Although the actual concern for indoor gardening is the delicate structure of Mexican Aster. This plant can easily break with basic movement. The long branch size of the plant makes it difficult to adapt to small spaces.

The blooming nature of Mexican Aster is another problem. It blooms at the tip of new growth. So you can’t prune the large stems to adapt them in small areas else the blooming will reduce. Pruning can be done after flowering ends.

Therefore, it is possible to grow Cosmos Bipinnatus indoors though it is not too easy. It will require extra care and nurturing.

Can Mexican Aster Plant grow in Containers?

8-10 inch garden pot is ideal for Mexican Aster.

Mexican Aster plants can easily grow in containers bigger than 8 inches. Any plastic or clay container is good to grow these wildflowers.

It only requires a big enough container, healthy moist soil, and direct sunlight. If you can manage all of these then you are good to go.

Mexican Atsers are very to grow in containers. In some cases, they even bloom better in containers. So it is worth to give a try. These wildflowers not only add color but also attracts butterflies.

You can mix-match Mexican aster plants with other flowers to create a beautiful living bouquet. It will require a 12 to 18-inch container to accommodate 1 Mexican aster plant with a couple of Cosmos, daisies, and other small flowering plants.

Don’t grow multiple Mexican Aster plants in small spaces or containers. They will compete for nutrients and reduce flowering.

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Temperature and Sunlight requirements

Mexican Aster seeds require 50 degrees Fahrenheit or more to germinate. The plant will grow best in 60 to 75 degrees Fahrenheit. Drop-in temperature can slow down the growth process. Too much heat can also harm the plants.

Therefore, the Spring season is best for Meican Asters. The temperature during these months remains under 75 degrees Fahrenheit that is ideal for Mexican Aster.

Proper sunlight is also essential for Meican aster. It is something that directly governs the temperature. 6 to 8 hours of direct, full sunlight is ideal for these wildflowers. Although they can easily survive and bloom in part shade.

Use the green net for Mexican Aster plants to grow late in spring especially in zone 10 and 11. Summer days in these zones are hotter where noon temperature can exceed 90 degrees. So either sow seeds early in spring or late in summer in these hardiness zones.

How much water does Mexican Aster Plant need?

The wild Mexican Aster flower prefers consistently moist soil during flowering. They can easily survive in low moisture though it is not good for blooming. Continuous or repetitive dehydration can stress out the Mexican aster plant. This can reduce new bud formation and flowering.

That’s Why it is better to irrigate the Aster plants whenever required. Deep watering is useful as it will drench the soil to sufficient depth. Also, it will allow a proper time gap for the soil to dry and new roots to dig deep in search of water. You should water only once or twice every week. Water deep and observe it flowing down through containers. Pour a little extra every time in the garden beds as the water gets spread easily within the soil layers.

Minimum 3/4 to 1-inch water is required for each Mexican Aster Plant per week.  Always test the soil for dryness before the next spell. Never keep the soil soggy else the plants may die due to root rot.

Propagation Method of Mexican Aster

Mexican Aster plants can be grown from their seeds as well as cut or seedlings. Seeds or seedlings are the obvious and common way to grow these wildflowers. You can directly sow the seeds in the soil or prepare them in a germination tray.

Small seedlings are easy to transplant though bigger ones are fragile and can break easily. The root system is strong enough for the propagation but the stems are prone to breakage. So shift them with care.

Cutting of Mexican Aster is not very easy to prepare. That’s why we don’t prefer it for growing these plants. Though you can make plants with cuttings. It will require time effort and some special tools. You have to use good quality rooting hormone to develop roots in the cuttings and this can take 3 to 5 weeks.

The Cutting method is not feasible as the blooming season is short and finding a healthy parent plant in the early season is not very easy.

Overall, seeds are the best option to propagate Mexican Aster plants.

Where to find Mexican Aster Seeds?

You have to visit a few garden stores and seed sellers to get the Meican Aster seeds. Mexican aster seeds are not available everywhere. Sometimes you may find these as a mixture of wildflower seeds. So if you want to get some healthy isolated Mexican aster seeds then ask your seed seller for availability. You can also check for Mexican aster seeds on Amazon.

Make sure the seeds are viable and packaged seeds just have viability date or expiry labeled on them. Check out for seed specifications before purchase.

How to Grow Mexican Aster?

  • Start with Soil Preparation. Mix 20% Garden Soil with 50% Compost and 30%cocopeat to germinate Mexican Aster seeds.
  • Use a 3 to 4 inches flexible plastic pot or seedling tray to germinate these seeds.
  • Fill the container with growing media and put 2 seeds in each. Two seeds will ensure germination, at least one of them will survive.
  • Keep the soil mix moist and warm for 4 weeks. Although Mexican Aster seeds start germinating within 2 weeks. Extra 2 week curation will ensure proper root growth.
  • You can start this germination process indoors at least 4 to 6 weeks before the last frost. Early germination will allow extra blooming time with the start of the season.
  • Shift the seedling out in the garden a week after the last frost.  Fall gardeners can directly grow Mexican Aster in the flower beds.
  • Transplant the seedlings to an open garden area where they can receive 6 to 8 hours of direct sunlight.
  • Maintain 12 to the 24-inch distance between two adjacent Meican Aster plants. Each row of Mexican Aster must have a consistent gap of 3 feet or 30-36 inches.
  • Feed these plants with balanced all-purpose fertilizer twice every month. Also, add 1-inch compost to the topsoil every month. This much fertilization is sufficient for blooming in Mexican Aster. If you want extra growth or blooming then add 10 grams superphosphate and 5-gram potash to each plant once every month. Although, extra use of fertilizer is not necessary if you use good quality soil or potting mix.
  •  Meanwhile, pinch off the tip of the first few branches to make the plant bushier. More branches mean more flowers. Though pinching is not recommended after the second month of plant growth. Be careful as late pinching or pruning can slow down bud formation.
  • Mexican Aster plant will start blooming within 50-60 days of germination. Meanwhile, take care of the plant and keep it healthy and free from pests.



Hi, My name is Sukant. I am an I.T professional. Gardening for me is not just a hobby, it's a way of living life with nature. My Ancestors were Commercial farmers: So I personally feel attached to the green. I am not an expert, I'm here only to share my gardening experiences. It's always Refreshing.

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