I have a velvet purple Cosmo from early summer and it flowered, but now its foliage is all green. Is this what it’s suppose to
do for winter?
Certified GKH Gardening Expert
It can. Usually, it will start to die out, though. This annual will self seed, so it will probably show up again next year. For now, you can enjoy its final stages of life and wait for next year's arrivals.
This article will help you to care for them: https://www.gardeningknowhow.com/ornamental/flowers/cosmos/growing-cosmos.htm