Are Cosmos Easy To Grow? Yes, Especially From Seed!

pink cosmos flowers and buds

Cosmos are one of the best flowers for new gardeners to try, but even experienced gardeners love to have a swath of cosmos in their garden because they’re just so easy to grow.

The wispy leaves and delicate-looking flowers add charm and color to any spot of the garden, and the blooms hold up well in the vase for arrangements. Even better, the display of blooms will attract butterflies and bees to your garden all summer long.

With so much going for them, why not include a few easy-to-grow cosmo plants in your garden this year?

Cosmos are extremely easy to grow, making them an excellent flower for the cutting garden. They are easy to direct sow in spring and summer, producing blooms in as little as eight weeks after sowing. Cosmos will happily grow in poor soil and require minimal water once established.

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Where do cosmos grow best?

To start growing cosmos in the garden, pick out a spot that receives at least six hours of sun per day. Cosmos love full sun and can grow well even in places that would overheat other summer annuals. If you only have a location in partial shade, you can give it a try, but be aware that the plants will probably not be as robust.

In addition to full sun, cosmos need frost-free weather for their growing season. Cosmos will not survive a spring or fall frost, so wait until the soil and weather have warmed up in the spring to sow seeds.

If you don’t know when to expect frost-free weather, you can quickly look up your frost dates on Farmer’s Almanac using your zip code. The dates are just an educated guess based on historical data, but they will give you a pretty good idea of when to plan for sowing your cosmos seeds.

butterfly on pink cosmo
Full sun will produce an abundance of blooms for you and the butterflies to enjoy.

Two other important factors in locating your cosmos plants are the soil and water requirements.

Cosmos do not need rich soil with regular fertilization. If the plants receive too much nutrition during their growing season, they will concentrate on growing foliage instead of beautiful blooms. Choose an area of your garden with just average soil, and don’t worry about fertilizing them throughout the growing season.

As for water needs, established cosmos plants only need to be watered every few days during the heat of summer. This amount will be enough to keep some moisture in the soil without overwatering them. Overwatering can lead to root rot and fungus issues. Cosmos like dry feet, so avoid choosing a spot that will retain too much water and stunt your plants.

Are cosmos easy to direct sow?

Cosmos are straightforward to direct sow, thanks to their large seeds and quick germination time. The seeds can be planted in rows or scattered sparingly and lightly covered with soil. Water the seeds in place with a gentle stream, and within a week, you’ll see cosmos sprouts.

Once the seeds start to pop up, take a look to ensure there is enough space between the plants. Cosmos will grow anywhere from two to five feet tall and can get very bushy. When growing cosmos for cut flowers, you can get by with 12-18 inches per plant since you’ll be cutting stems regularly.

If your seedlings are closer together than a foot, wait until the plants have at least one set of true leaves, then you can gently transplant them farther away. The true leaves are the lacy, frond-like leaves you’ll see within a couple of weeks from germination.

cosmo seedling with several true leaves
This is a good size to move any seedlings that are too close together.

If you are trying to get a head start on your growing season, you have the option of starting cosmos seeds indoors. This will give you a 4-6 week advantage on the growth of your plants, resulting in blooms about a month sooner than if you direct sow them.

To start cosmos indoors, you will need to have a strong light source to avoid the cosmos getting leggy, which means having long, thin stems. Leggy seedlings develop when the seeds sprout and reach a light source that is too far away, such as when they’re grown on a windowsill.

With a simple shop light and 14-16 hours per day of light per day, you will have healthy, vigorous cosmos seedlings to transplant into the garden after your last spring frost.

Can you grow cosmos in pots?

Easy-to-grow cosmos are perfectly suited for growing in pots. Shorter varieties such as Xanthos or Xsenia will be easier to manage in medium-sized pots. Still, taller varieties such as Versailles Mix or Double Click Cranberry will grow just fine with a larger container.

white cosmos growing in a pot
Don’t let the lack of garden space stop you from growing cosmos. They’ll do just fine in containers.

Cosmos grown in pots have the same requirements as those grown in-ground. Don’t use very rich potting soil to avoid excessive leaf growth. A regular potting soil without additional fertilizer will ensure you get plenty of blooms.

When the plants are small seedlings, make sure they receive regular water and plenty of sunlight to develop into vigorous plants. Once the plants are well established in the pots, you can give them less water if you need to, and it won’t faze them.

Try planting several pots with different colors of cosmos to make a colorful tapestry of cosmos flowers for your container garden.

Do cosmos come back every year?

Cosmos are not perennials, so they do not reliably come back every year. However, cosmos are prolific self-seeders, meaning that the seeds produced by the plant will easily drop and sprout, creating new plants. Some seeds may survive the winter, growing new cosmos plants the following spring.

It’s worth leaving some spent blooms on the plant at the end of the season, especially if you’d like to keep cosmos growing in the same spot the following year. You can even take a few seed heads and scatter the seeds in a new area where you would like to have cosmos bloom.

Now that you’ve (hopefully!) decided to include cosmos in your garden this year, be sure to get some tips for keeping them blooming all summer long in this post, Do Cosmos Bloom All Summer: How To Keep Them Flowering.

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