How To Plant And Grow Cosmos From Seeds

beautiful pink, white, and purple cosmos in a field

Cosmos seeds produce hardy flowering plants that thrive with heat, sun and little water. These annual varieties grow anew each year. They come in colors from white to yellow to red and grow to heights ranging from 2 to 7 feet. There is a cosmoses variety to suit any garden. While growing a flower from seed might sound like a difficult task, cosmos are so easy to grow and require so little attention that you can easily fill your garden with them.

Starting Seeds Indoors

Hot weather and hot soil are the triggers that get cosmos seeds going. It takes about 50 to 55 days for the seeds to germinate, grow and start blooming. If you want to get a head start on your cosmos before the weather warms enough, plant your seeds in a tray indoors.

Start 4 to 6 weeks before you expect to be able to plant your cosmos outside. Fill the tray with any standard potting soil. Do not worry too much about fertilizer and heavy nutrients because cosmos do better without a lot of nutrients.

Cut a small trench through the center of the tray and plant the seeds 1 to 2 inches apart. Cover the seeds with a thin layer of soil and tamp lightly. Water gently, then put the tray under a sun lamp.

Provide at least 12 hours of light per day. When you have visible seedlings, consider moving the tray to a window, as long as it continues to get enough light. Once the weather warms, you can plant your seedlings in your garden.

Planting Outdoors

Prepare your garden plot for your cosmos. Remove the weeds. Ensure the soil is well draining and do not add fertilizer. You have 2 options:

Cut small trenches in the soil. Place the seeds inside the trenches at a 1 to 2 inch spacing. Cover the trench with a light layer of soil.

Sprinkle the seeds over the soil. Rake the soil lightly to cover the seeds and ensure contact between seeds and soil.

Water the area you have planted. Keep the soil moist for several days, but not soggy. The warmer the soil, the faster your seeds will germinate and grow.

Continuing Care

Cosmos do best with tough love style care. Water them only when they are wilting. Choose a location where they will get lots of sun every day.

Your cosmos can continue blooming from spring to first frost. You can deadhead as each flower wilts if you have a small planting, or you can cut the plants down when there are more seed pods than flowers. Cut the plants back to 12 or 18 inches tall. Within a month they will be back to full height and blooming again.

Preparing for Next Year

There are 3 options for seeding for the next year's growth.

Buy fresh seeds yearly.

Save the seed pods from when you deadhead, especially from the final blooms of the season. Put them in a paper envelope and keep the in a cool, dark, dry place until it is time to sow them for the spring.

Let the seeds scatter over the ground from your flowers. Early blooms may produce seeds that grow that year, thickening your clump of cosmos. Later blooms will sleep through the winter and grow in the spring.