Cosmos: You Can Grow That!

Cosmos are the annual gifts that keep on giving. And that’s good, because they’re one of the easiest flowers to grow and they come in a huge range of colors, bloom types and varieties.

Cosmos (Cosmos bipinnatus) plants are part of the Aster family, and native to Mexico and some areas of the desert Southwest. Between this classic cosmos and the related sulphur cosmos (C. sulphureus), the flowers can grow in nearly a full range of growing zones – from zone 1 through zone 11.

sulphur cosmos flower orange
Sulphur cosmos in bright orange.

Of course, in nearly all but the hottest of these zones, cosmos grows as an annual and dies back with frost. But if you think that is a good reason to avoid growing the plant, I’d like to convince you otherwise. Cosmos is a prolific re-seeder in even the poorest of garden soils.

cosmos in xeric garden pink
Cosmos that have re-seeded every year for at least five years.

Add Color and Wildlife

Cosmos flowers attract butterflies and hummingbirds, along with other insects. They will bloom from mid-summer through early or mid-fall, depending on your first frost date. You can cut flowers for indoor arrangements, which also can lead to more blooms. I also leave plenty of dying flowers on the stems because they feed finches. I love watching a finch land on the small, swinging branches to peck away at the seeds. In a world in which so many flowers are yellow, it’s so great to enjoy the white, pink and red tones of cosmos in my xeric garden.

Butterfly on bright pink cosmos blossom.
Butterflies and bees love cosmos flowers.

Plant from Seeds

You can plant cosmos from seeds or nursery transplants. I have had mixed luck growing cosmos from seed until this year. I know the flower seeds like loose soils, but with our dry and windy conditions, I found it better to cover the seeds lightly with some compost and water with a soaker hose to prevent washing away.

As for planting again next year, unless you severely disturb the soil where (and near where) you had cosmos last year, you should get plenty of volunteers as soon as summer rains start, and see the seedlings with their fine leaves growing taller as monsoon rains continue. You can help Mother Nature by gently spraying the area where you want the flowers to appear if early-summer rains have been light.

bright pink cosmos flowers
Re-seeded cosmos flowers have maintained their bright colors.

Most cosmos varieties grow tall, maturing at up to four-feet high, so they often work best at the back of a garden.  If you have a bed or meadow filled with cosmos, they tend to support each other and seldom flop over as some plants can when they get tall. Cosmos loves full sun or part shade.

Sit back and enjoy

Once they become seedlings, cosmos do best with nothing but rain water. Overwatering the plants actually can lead to fewer blooms.

red-pink cosmos flower
The tiny needle-like leaves of cosmos and upright growth make the seedlings easy to spot.

There are some areas of the United States that consider cosmos invasive, including a few spots in western New Mexico. And I admit one of the best characteristics of the plant – easy re-seeding – also can mean it pops up where we don’t want it. For example, if I didn’t pull seedlings out of our steps, we would not be able to walk down to the garden. But I leave a few off to the side for compromise. I pull those that block other plants and let the rest grow as they may. They’re crowded, but I love the effect.

cosmos, babys breath, cornflower in small vase
Cosmos as part of some cut flowers adorn my desk on days when I can’t spend much time outside.

You can grow cosmos and enjoy cutting the flowers for indoor arrangements. And have even more fun watching for new flowers to begin popping up the next summer!

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