Cosmos are a beautiful annual that self-seeds and is drought resistant. Cosmos flowers are a favorite for bees and butterflies, and the more flowers you cut, the more they will bloom throughout the summer and fall.
Although cosmos look delicate with their thin stems and ferny leaves, they are very resilient and are perfect for cottage, wildflower, and cutting flower gardens.
Originally native to Central and South America, cosmos flower seeds were taken back to Europe, where they were cultivated in gardens. Their popularity grew, and they were spread throughout the world.
Heirloom Cosmos Varieties
Each variety of cosmos has a unique petal color or shape. They can all be grown together for a beautiful array.
How to Grow Cosmos Flowers from Seed
Cosmos are one of the easiest flowers to grow from seed. They will flourish in poor soil, are drought tolerant, and self-seed if flowers are left on the stem.
Cosmos are frost sensitive, so wait to sow seeds outdoors until after the last spring frost has passed, and the soil has warmed to at least 65ºF.
For earlier blooms, you can start cosmos seeds indoors 3-4 weeks before the last frost date.
Indoor Seed Starting Tips:
Plant seeds 1/4” deep.
Keep soil moist but not soggy.
The optimal soil temperature for seed germination is 68-72ºF.
Seeds will sprout in 10-15 days.
Keep a grow light close to the plants. This will keep them from stretching towards the light and becoming leggy.
Transplant cosmos seedlings to a sunny location with well-draining soil after all danger of frost has passed.
Be careful not to disturb the roots to avoid transplant shock.
Space cosmos plants 12 to 18 inches apart.
How to Care for Cosmos Flowers
Cosmos flowers are truly low-maintenance. They tolerate drought, don’t need fertilizer, and will self-seed. Cosmos grow fairly quickly and will have blooms 50 to 60 days after they have sprouted.
Cosmos will thrive in full sun. They are native to Mexico and Central America and can tolerate the hot summer sun. A minimum of 6 to 8 hours of direct sunlight is needed daily. Cosmos plants will produce fewer blooms if grown in shady areas.
Cosmos don’t need to be spoiled with rich soil. They will flourish in average garden soil with a neutral to alkaline pH. Cosmos also don’t need extra fertilizer as it will only produce more foliage, but not more flowers. Adding compost before planting or transplanting will be sufficient for the whole growing season.
Don’t overwater Cosmos. These plants are used to arid conditions and don’t need consistently wet soil. Cosmos can tolerate drought once they have an established root system. You will want to give them sufficient water to keep them stress-free and blooming, but usually no more than once a week.
Staking and Support for Cosmos
If you are growing cosmos in a cutting garden, you will need to put in supports early. These fast growers can easily reach 6 feet tall and be knocked down in a windstorm or heavy rain.
Netting about 2 feet above the ground gives a supportive space for the plants to grow up through. They can also be tied to stakes.
When growing cosmos in wildflower or cottage gardens, you can plant other flowers nearby to help hold them up.
Deadheading and Pruning Cosmos
Cosmos are a prolific “cut and come” flower. Regularly cutting blooms will encourage more buds to grow. Deadheading and cutting cosmos flowers will keep seed heads from forming and lengthen the plant life.
To encourage branching, pinch off the top growth when the cosmos plants are still small, about 12 inches tall. The increased number of branches will produce even more flowers.
If you want to save cosmos seeds, leave flowers on the stems, and they will form seed heads. Once seeds are dry, they will drop to the ground and grow a new crop of flowers.
To collect cosmos seeds, gather the seed heads before they burst open and place them in a paper bag to continue drying. Seeds can be stored in a cool, dry location for planting next season.
Harvesting Cosmos Flowers
For optimal blooming, you want to cut or harvest your cosmos regularly.
Cosmos flowers can be cut as soon as the color is evident but before the bud has fully opened. There will be several flowers on each stem, so you will have a variety of stages, which makes for a longer vase life.
For the longest vase life, cut cosmos flowers early in the morning when they are still fresh and after the dew has dried a little.
FAQs about Cosmos
Do cosmos come back every year?
Cosmos flowers are an annual, meaning they only grow for one year. However, they will self-seed if flowers are left on the plant and allowed to produce seed. This makes them an excellent choice for cottage and wildflower gardens.
What is the best month to plant cosmos?
Plant cosmos in the spring and summer months when there is no danger of frost. They are a warm weather flower.
Do cosmos spread easily?
Cosmos spread by dropping seeds.
Cosmos are one of the easiest flowers to grow from seed. Not only that, they are prolific bloomers that you can cut often and enjoy indoors. As long as you keep them from going to seed, you’ll have blooms until the first fall freeze.
Start growing cosmos if you’re looking for a prolific blooming, easy-to-grow flower. These low-maintenance beauties are the perfect flower to add this year.
Written by Beverly Laudie
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