cosmos flowering in a field

How To Grow And Care For Cosmos

Cosmos are freely blooming annuals that may be grown by spreading some seeds in the garden after any frost threat has gone. This traditional cottage garden blooms mature in around two months. Cosmos may take longer to germinate, but it blooms immediately and continues to flower into the fall. All summer, the flowers perch atop long, thin stalks, creating a cloud of stunning color that attracts butterflies, bees, and birds to your garden. Cosmos blossoms resemble daisies. They come in a variety of hues, with additional varieties being produced each year.

Growing Cosmos

Cosmos has about 25 different species. Three kinds, however, are the most prevalent in gardens and landscaping. Central America, Mexico, and northern South America are home to Cosmos sulphureus. Cosmos blooms range in size from 3 to 5 inches and come in a variety of hues, including pink, white, orange, red and yellow, and maroon. Their flowerheads might be bowl-shaped or open-cupped. These lovely plants may grow up to 6 feet tall.

Cosmos thrive in both beds and pots, and they make excellent cut flowers.

Here are some brief facts about the popular aesthetic plant:

  • Latin name: Cosmos sulphureus, Cosmos bipinnatus 
  • Other names: Cosmos, Mexican aster, cut-leaf Cosmos
  • Native to: northern South America, Central America, and southern North America
  • Invasiveness: Yes
  • Tenderness: herbaceous perennial plants or annual plants 
  • Sun: Full Sun
  • Water: As required
  • Soil: Well-draining soil
  • Hardiness zone: Zones 2 through 11
  • When to plant: Spring
  • Spacing: 12 to 18 inches
  • Plant height: 1-6 ft. 
  • Bloom period: Summer through fall
  • Time to maturity: 3 months
  • Container friendly: Yes
  • Fertilizer: Not required
  • Toxicity: No
  • Deer resistant: Yes
  • Pest resistant: Yes

Cosmos grow well in beds and produce excellent cut flowers. When the plants are established, they can withstand drought, poor soil conditions, and general neglect. They can even self-seed. This is a plant that requires very little care.

While certain pests eat on Cosmos, such as aphids, flea beetles, and thrips, they are easily controlled with a powerful spray of water or insecticidal soap. The Cosmos may also be affected by bacterial wilt, aster yellows, and powdery mildew. Plants should be spaced appropriately to allow excellent ventilation and disease prevention.


Unless there is a protracted drought, you will not have to hydrate your Cosmos plants after they are established. They are among the last plants that need irrigation when water is scarce.


Choose a location that receives full light for the finest blooms. Cosmos will thrive in partial shade, but will produce fewer flowers and be less vigorous. These plants will also survive in full sun over long periods under the warmest temperatures, similar to their natural home in Mexico and Central America.


Cosmos plants like neutral soil with a pH range of 6.0 to 8.0, but they will thrive in poor soils where many blooming plants fail. They thrive in moderate moisture, and well-drained soils, but will also do well in dry soils. Planting in rich soil might lead plants to grow overly tall and flop over. Drooping may be avoided by anchoring the plants or growing them near other plants that can assist them.


Fertilization can have a harmful influence on the plant. It can grow on poor soil. Excess fertilizer can typically result in vigorous plants with a lot of foliage but few flowers. These plants do not require fertilizer unless they appear to be in distress.


If you live in the southern United States and want to grow Cosmos, keep them in pots since they can be invasive. The Southeast Exotic Pest Plant Council of the United States labeled this plant invasive in 1996. Cosmos bipinnatus, a post-monsoon invader, may wreak havoc on the local wildlife. In the southeast United States, Cosmos sulphureus has become invasive.

Growing Cosmos In Containers

When growing Cosmos in a container, ensure sure it has bottom holes in the bottom. Cosmos cannot tolerate too moist, soggy soil. Prepare to cultivate one Cosmos plant per gallon of the container. Growing plants in containers do not nourish the soil and cause them to become tall, lanky, and drooping. Tall cultivars will also require staking in containers. Plan on using a hefty, 12-inch-diameter container at the very least.

Care & Tips

The plants require direct sunlight to blossom. Even a sliver of shadow might prevent flowers from blooming. You could also deadhead the old blossoms to stimulate fresh blooming. Prune between the main stem and a leaf for quicker flowering. The lower the stem is cut, the longer it takes for additional blossoms to grow. You’ll need a strong full sun growth lamp for at least 7 hours a day if you have a potted Cosmos in a container and want to maintain it alive during the winter. Any flowers that appear will need to be snipped off. The life cycle of this plant concludes with blooming when it produces seeds for the following growing season.

Common Problems

They are simple to grow and care for throughout the growing season. They are typically resistant to illness and most insects; nevertheless, some pests can become a nuisance and hinder their growth. If your plant gets enough water and is not withering from dehydration, there are two possibilities.

A withering plant with leaf yellowing may have a common fusarium fungal infection. Powdery mildew primarily affects plants that grow in the shade. Fungus spores travel through the air and adhere to a shared host plant. It coats the leaves with a powdery white covering, causing them to yellow and fall off.

Propagating Cosmos 

They self-seed rapidly. It is recommended to propagate these plants once the danger of frost has passed. Although planting seeds is the best and easiest technique to propagate this plant, stem cutting can also be used. Taking stem clippings encourages increased leaf and flower development. Aside from seed, the easiest technique to reproduce this plant is by stem cutting.

Wildlife attracted by Cosmos

Their open blooms make it simple to get nectar and pollen. In your garden, you can never have too many pollinators and predatory insects to assist pollinate and manage pests. Beneficial insects like lacewings, tachinid flies, parasitic wasps, and hoverflies are drawn to its blooms because they prey on problem insects and give free pollination. It’s also loved by Monarch butterflies.

Uses For Cosmos 

In temperate region gardens, the species, as well as its variations and cultivars, are popular as decorative plants. Cosmos sulphureus (C. bipinnatus, C. caudatus, or Mexican Aster) petals are edible and enhance salads if grown from organic seeds and without pesticides. If you re-cut the stems and put them in freshwater, these blossoms can live up to 7-10 days.

The connotations of its flower include order and harmony, benevolence, beauty, resilience, self-reliance, and infinity. Cosmos are simple to germinate, cultivate, and self-seed the next growing season. If this annual isn’t in your garden, it should be! This low-maintenance plant thrives in the sun and heat, providing stunning color in return.

Mayukh Saha
Freelance Writer
Mayukh is a Content Marketer and Social Media Manager with over 5 years of experience in the industry. Mayukh believes in the power of content; how it can positively impact lives, scale businesses and touch people. In his spare time Mayukh likes to read about latest tech trends and loves to travel in the nature. You can reach him at [email protected].