Your cosmos winter care depends on which type you're growing. Most cosmos are annuals that die after the first hard frost. You can pull them up and compost your plants once they turn brown. Chocolate cosmos is the exception since it grows from tubers that need special storage to survive.
In my experience, letting annual cosmos stand through the first few frosts works best. The dried seed heads feed your winter birds and add some texture to your bare garden. When you finally clear them out, shake the seed heads over the bed to scatter seeds for next year's volunteers.
For cosmos end of season cleanup, you have two choices with annual types. You can pull your plants after the first frost and compost them. Or you can leave them standing until spring if you want seeds to scatter and self-sow. Either approach works fine for you. Choose based on how tidy you like your winter garden to look.
Saving your own seeds takes just minutes and gives you free plants next year. Wait until seed heads dry and turn brown on the plant. Snip them off and drop into a paper bag. Shake to release the needle-shaped seeds. Store in a cool, dry spot until your spring planting time arrives.
Overwintering cosmos gets more complex with chocolate cosmos since this type grows from tubers. These tender perennials can't survive your freezing soil. In zones 9-11 you can leave them in the ground with mulch protection. Everyone else needs to dig and store the tubers indoors for winter.
Storing chocolate cosmos tubers works just like dahlia storage. Dig them up after the first frost kills back your foliage. Brush off loose soil but don't wash them. Let them cure in a dry spot for a few days. Then pack in peat moss or vermiculite and store at 40-50°F (4-10°C) until spring.
I tested different storage spots and my basement works best where temps stay steady all winter. Check your tubers monthly for signs of rot or shriveling. Mist lightly if they look too dry. Replant your tubers after your last frost date when soil warms up again.
Don't stress too much about getting cosmos winter care perfect. Annual types are so easy to grow from seed that losing plants to frost is no big deal for you. Just save some seeds and you'll have cosmos again next summer with almost no effort at all.
Read the full article: Cosmos Flower Care: Complete Growing Guide
