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Summer Flowers: Cosmos

Cosmos are another summer must-grow for your garden. They are easy to grow, beautiful flowers that do not require much attention. They make an excellent cut flower and will reward you with more flowers the more you cut. Learn all about how to grow this whimsical and delicate flower below.

A blue and white pitcher of pink, light pink, and white cosmos

Our story

We have been growing cosmos on the farm since the first serious year of flower growing. That year, the soft, pastel hues of the cosmos I grew hooked me. I loved the way the blooms danced above bouquets and offered a delicate touch to arrangements.

We have particularly enjoyed growing cosmos of the double click variety. These flowers look like small, frilly tutus dancing in the wind.

We will always have cosmos growing as they are easy to start from seed indoors or by direct seeding outdoors. In fact, they often reseed themselves. I have transplanted volunteer seedlings with great success.

Another great thing about cosmos is that pollinators love these flowers.

White cosmos with a butterfly on the plant

Care & Maintenance

As an annual, cosmos can be started from seed in late spring into summer. You can sow seeds directly into the ground once the ground is warm enough or plant out seedlings after starting them off indoors and hardening them off. I start seeds indoors in order to start them a little earlier and get them in the field as soon as the weather is warm.

Plant seeds in a sunny location 9" apart if growing for cut flowers. You can space out seedlings if you are growing them in your yard or garden. Make sure to pinch your seedlings to get more flowers.

Fertilize seedlings with a foliar spray of fish emulsion and weed tea once a week until plants develop buds. A preventative foliar spray of milk will help reduce the growth and spread of powdery mildew.

An arrangement of dahlias, zinnias, orach, and cosmos


Harvest cosmos early in the morning or in the evening. Harvest into a clean bucket of cool water using sharp and clean snips.

Harvest flowers when the bloom is just starting to open. This way, flowers will have a longer vase life.

Cut deep into the plant to encourage it to make longer stems. Begin by cutting the main shoot just above a set of leaves. Later in the season, cut from side shoots just above a set of leaves.

Make sure to harvest cosmos regularly so the plants continue to flower. Once the flower dies back on the stem, the plant begins to create seed and stops flowering. If you keep harvesting flowers, the plant will continue to produce flowers.

Cranberry double click cosmos

Other things to consider

I have found that our cosmos will usually get powdery mildew every year with the rainy season we have in July. I tried planting them out a little later this year with that in mind. As mentioned, you can use a foliar spray of milk and water to help prevent powdery mildew.

Cosmos will need to be staked or corralled in some way. With consistent cutting, the plants can get big. Make sure to grow them using netting, a cage, or use twine and stakes to contain them in one space.

Cosmos will be a wonderful addition to your yard or garden. Try planting them this summer for beautiful color and joy in your life.

This post is part of a year-long series on flowers and plants that we love and grow on the farm. Check out other flowers that we love.


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