Cosmos is one of the cutting garden’s most popular and heaviest-producing flowers. They are also one of the taller plants you might grow. Knowing how tall cosmos grow can help you decide which varieties are best for your garden and where to locate them.
Cosmos most commonly grow 40-48 inches tall, though their height can range between 20-54 inches tall. Sun exposure, soil health, and irrigation will have a role in the final size of any cosmos variety. Shorter cosmos varieties are suitable for pots, while tall ones might need to be staked.
The following tips will help you dial in the steps you can take to grow the most robust cosmos and choose the varieties that best suit your garden.
How tall do cosmos get?
The average height for cosmos is right around four feet tall. Dwarf varieties will top at two feet tall, while the tallest plants may reach almost five feet tall. Choose a variety that will fit your requirements depending on the space available in your garden and how you want to use the blooms.
|Cosmos variety||Days to maturity||Flower color||Plant height (inches)|
|Versailles Mix||90-110||pink, white, red||40-48|
|Cupcakes Mix||90-100||pink, white||40-50|
|Double Click Cranberry||75-90||deep cranberry red||42-46|
|Double Click Bicolor Violet||75-90||cream, pink||42-46|
|Japanese Kiiro||75-90||cream, yellow, pink||42-48|
|Sensation Mix||75-90||pink, white, red||48-54|
Dwarf cosmos varieties
Dwarf cosmos are varieties that have been bred to remain short. Even if grown in optimal conditions, they’ll never be the tallest plants in the garden. Dwarf varieties are excellent choices for smaller gardens or if you’re looking for a variety suitable for growing in containers.
Xanthos and Xsenia are two options if you want shorter plants. I have a packet of Xanthos seeds in my stash, and I’m looking forward to growing this new-to-me variety this spring. Plus, those buttery yellow petals are a nice change from the typical pink and white shades that cosmos are known for.
Mid-height cosmos varieties
Cosmos in the middle height range of 42-46 inches have the most varieties to choose from. No matter what color scheme you are designing in your garden, you’ll find a variety that works for you, from cranberry red to snow-white and single blooms to pouffy double flowers.
Cupcakes Mix is exciting. The petals are crinkled to look like cupcake papers with slight ridges. Charming colors of pink and cream, and yellow centers make this an excellent variety for romantic displays. Fizzy White has similarly fluted petals but in white and with tufted centers.
For bolder colors, Double Click Cranberry is a great choice. The blooms develop as semi-doubles and doubles at a height of 42-46 inches. This means that instead of a single layer of petals on the bloom, the flowers have a double row of petals, making them look fluffy and rounder. Both types of blooms are deep cranberry red with yellow centers.
Here are Cupcake Mix, Fizzy White, and Double Click Cranberry from Johnny’s Selected Seeds. All the texture and color you could want!
Tall cosmos varieties
At the tallest end of the spectrum, the classic variety Sensation Mix will tower over your other plants at almost five feet tall, or 54 inches. This variety is known as “garden cosmos” and is ubiquitous in cottage gardens. Long-lasting blooms in pink, white, and red make this variety a great choice if you have room for it.
As you can see, the combinations of height and color are (almost!) limitless.
Sunlight, soil, and water will influence your plants’ height
No matter which variety of cosmos you choose to grow, it won’t reach its full potential if the right growing conditions aren’t met. Cosmos are pretty easy-going when it comes to their growing conditions, but it doesn’t hurt to optimize them.
Cosmos sunlight requirements
Cosmos are sticklers when it comes to the amount of sunlight they get. Native to the Southwest United States and Mexico, cosmos can handle heat and sunlight. They thrive in at least 8 hours of full sun per day, and this amount will affect how tall the cosmos grow.
If grown in partial shade, which is only 4-6 hours of sunlight per day, the plants might not reach their full height or be as robust. The stems are also likely to be shorter, giving you few options for arranging cut stems in bouquets and vases.
Cosmos soil 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 reaching their maximum height covered with beautiful blooms. Choose an area of your garden with just average soil, and don’t worry about fertilizing them throughout the growing season.
Pro-tip: Cosmos grown in too-rich soil might bloom less than those grown in poorer soil. Find out why in this article, 4 Reasons Your Cosmos Aren’t Flowering (And How To Fix It).
Cosmos water requirements
Water is another factor that can affect how tall cosmos grow. Cosmos do not like to be overwatered or have “wet feet.” This means they need well-draining soil that won’t retain water around their roots. If cosmos are overwatered, it will stress the plants, and they may not reach their full height potential.
Overwatering can also lead to root rot and fungal disease, which will almost certainly negatively affect how well the plant can grow.
A stressed plant is also more susceptible to pests and disease, which will affect the plant’s growth and the quality of the blooms. If a plant is fighting off aphids or beetles, it won’t thrive and achieve its full height. Even if it does grow tall, pests like beetles eat the leaves, making them unusable and weakening the plant.
Cosmos are one of my favorite flowers, so I love to write about them. These articles can help you grow the best flowers, too.