Most cosmos varieties are one-hit wonders that won’t make it through the winter. Even the perennial types need a little extra TLC to survive the cold months. If you want to keep your cosmos coming back year after year, here is everything you need to know about overwintering them.
Which Cosmos Varieties Can Actually Overwinter?
Only a few types of cosmos are true perennials capable of blooming again the following year. The most popular one is the Chocolate Cosmos, famous for its deep red color and delicious chocolate scent. Fun fact: the flowers are actually edible! Unlike the common annual varieties, perennial cosmos grow from root tubers. However, these tubers are not cold-hardy and will die if they get hit by a hard frost.
How to Overwinter Your Cosmos
Once autumn temperatures dip down to about 60°F (15°C), your cosmos will start losing their blooms. That’s your signal to get them ready for their winter nap. Here’s the game plan:
- Dig up the root tubers carefully.
- Store them in a frost-free spot at around 40°F (5°C).
If you’ve been growing your cosmos in containers, you’ve got it easy! Just move the whole pot into a frost-free room. Cut the plant back at the start of winter and give it a tiny sip of water every now and then—just enough so the soil doesn’t bone-dry.
What about the annual types? While the plants themselves won’t survive the freeze, they are champion self-seeders. You can collect and dry the seeds for sowing next spring. Just keep in mind that these seeds aren’t always “true to type,” so you might get a fun surprise when it comes to their color or shape next year!
When Can They Go Back Outside?
You can start starting your seeds indoors as early as March. This is also the perfect time to wake up those perennial tubers by planting them in pots indoors. Wait until mid-to-late May—once the danger of frost has completely passed—before moving your cosmos back out into the garden beds or leaving the pots outside for the season.
