How To Grow Cosmos Flowers, Which Will Bloom All Summer In Your Garden
Bright and breezy, Cosmos are a favorite among gardeners for a reason. Blooming in shades of pink, white, purple, and even orange, these tall flowers bring a pop of color to your property that lasts from mid-summer straight through the first frost.
So, whether you’re aiming for a relaxed wildflower feel or just want to add some vertical interest to your outdoor space, here’s how to grow and care for Cosmos.
Cosmos Care
Before we dive into care requirements, it’s important to point out that there are several varieties of Cosmos to choose from. And by mixing different types, you can create a really dynamic garden display.
One popular pick is Cosmos sulphureus, which usually boasts sunny yellow and orange blooms. It also reaches an impressive four to seven feet in height. Another smaller option is Cosmos bipinnatus, which features pink, white, and purple petals and reaches between one and six feet tall.
Regardless of which variety you select, this plant is pretty easy to grow from seed. You’ll want to choose a sunny spot with well-draining soil, then scatter the seeds evenly over the surface.
Next, use a rake to gently push the seeds about 1/16 to 1/8 inch deep into the ground before adding a light covering of soil or vermiculite. One thing to note is that a main reason why Cosmos are so beginner-friendly is that they aren’t super fussy about soil.
In fact, as long as the soil drains well, they’ll do just fine, even in poor or sandy soils. However, if your garden is particularly sandy, mix in a bit of compost before planting.
Once you’ve covered your seeds with soil, press lightly to ensure there’s solid seed-to-soil contact. At that point, you can also water thoroughly.
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But while Cosmos needs regular, consistent watering to get established and germinate, they’re fairly drought-tolerant once mature. So, after your plants are well-established, you can scale back on watering.
In terms of temperature, Cosmos does well in warm weather with consistent heat. They germinate best when soil temperatures are between 70°F and 72°F. That’s why many gardeners opt to start seeds indoors about five to seven weeks before their region’s last frost date.
If you choose to go this route, you can move your plants into your garden when the soil outdoors warms up to at least 60°F. Just avoid transplanting them too early, since Cosmos are very sensitive to the cold.
Finally, once seedlings start to appear, it’s crucial that you thin them out. That way, your plants are spaced 12 to 24 inches apart, allowing them plenty of room for airflow and growth. Cosmos are generally resistant to most pests and diseases, but if they’re planted too densely, it can lead to poor air circulation, which causes powdery mildew.
A second common issue with this variety is a lack of support. Since Cosmos grows tall, you should consider planting them near a fence or wall, or adding some stakes to help keep them upright.
And if you’re a big fan of flower arrangements, you’ll be able to visit your own garden for your next Cosmos bouquet. To harvest single-petal varieties, you can cut them just as the buds are beginning to open and show color. Otherwise, double varieties should ideally be harvested when the flowers are half open.
Just remember to use clean, sharp scissors or pruners and place the cut stems into water immediately to help your arrangement last as long as possible.
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