Answer: Cosmos are annuals. They self-sow very prolifically so sometimes they are mistaken as perennials. If you left them be until they produced seed and the seed dropped, you will most likely see some sprouting in the spring. The seedlings look like tiny asparagus ferns when they first appear. I'm not sure why the catalog offered cosmos as a perennial...there is a variety of cosmos called a Chocolate Cosmos that grows from a tuber that is dug up every year and replanted...perhaps this is the one you have? If not, you have an annual cosmos.
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