Grow Cosmos


Cosmos is a ridiculously easy-to-grow summer flower that comes in so many varieties it’s hard to choose between them. It is durable when cut, blooms all summer, and readily self-seeds where it thrives. No wonder cosmos is many people’s darling in the flower world.

All these lovely colors

Cosmos originally comes from Mexico. With the 16th-century maritime trade, the flower came to Spain where it was first grown in monastery gardens. The flower was named Cosmos because its petals are so symmetrically and orderly arranged.

Cosmos has been bred over a long time. Today there are many different delightful varieties. It can be single-flowering or double-flowering and constantly appears in new shades. White, cream-colored, pink, burgundy, orange, and so on. We find more favorites every year.

The large flowers make cosmos an excellent attractant plant that attracts butterflies and bees to the garden.

The lower varieties, 30-40 cm, do very well in a pot. Other varieties can grow over a meter high. With its brittle, feathery foliage and many flowers, cosmos easily fills out a flower bed and needs no support to grow.

Indoor pre-cultivation of cosmos

For early flowering, cosmos can be pre-cultivated indoors from March to April.

Scatter the seeds in seed soil, lightly cover with soil and keep moist during germination. When the leaves have emerged, the plants thrive best in a bright and cool environment. Thin out any that may have ended up too close together.

When the plants have grown, it’s time for repotting. Plant them a little deeper in the new pot. They will be less gangly and develop strong roots.

When the risk of night frost is over and the daytime temperature is at least 15 degrees, it’s time to plant out the pre-cultivated cosmos. Harden off the plants first by letting them be outside a little longer each day. This way they gradually get used to sunlight and outdoor climate. After that, they can be finally planted in a warm place in sun or partial shade.

Each cosmos will form a bushy foliage with many branches. Therefore, it’s good to have about 25 cm distance between each plant. Cosmos grown in pots can be planted a bit closer together.

Winter sowing of cosmos

Cosmos is one of the plants that tolerates cold and is suitable for winter sowing. December to March can be a suitable time for sowing. When winter sowing, it’s good to cover the soil with a little snow. Remember to water in the spring, when the soil dries up and the seeds are ready to germinate.

Direct sowing of cosmos

Cosmos also works very well to sow directly in the growing site in May. Prepare by removing weeds, loosening the soil a little, and watering. Then scatter the seeds evenly and cover them about 1 cm deep. Keep moist during germination. Thin the plants to about 25 cm apart.

Hardy and undemanding

Cosmos thrives best in full sun, but a partially shaded location also works well. It is a hardy plant that usually survives well from diseases or pests. It also has no specific soil requirements, but does well in fairly poor soil. Too much fertilizer can make them develop more foliage than flowers. A basic fertilization usually suffices.

Top the plants when they have grown and developed a few pairs of leaves. This stimulates them to branch out and become bushy. Also cut off wilted flowers. But allow some to go to seed to prepare for the next growing season. However, it’s good to know that bred cosmos tend to revert back to their base colors. So don’t be surprised if the seeds produce flowers in a different color than the flower they were picked from.

Around midsummer, the blooming begins. Cosmos then generously produces flowers until the frost arrives. It is a wild garden gem that is very durable as a cut flower.


Author: Johanna Damm

Fact-checked by Erik Hoekstra

Last updated 2022-10-14

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