By Gerberavicki
Berkshire,
United Kingdom 
i have several cosmos in pots ready to go into my garden. i have never grown them before but am surprised by how long the flowers last - not!!!! i am deadheading them everyday! are they always that short lived? and i have read that some are perennial and some bi annual, i thought they were perennial! i actually have about 15 of them so i hope so!!!!
7 Jul, 2011
Answers
Cosmos are annuals, as they cannot survive winter here in the UK - they come from dry parts of Mexico originally. Perhaps you are deadheading so much as they are in pots rather than in the soil? My flowers seem to last ages, though I am quite neglectful of them.
7 Jul, 2011
They do bloom best in a lean, sandy soil.
8 Jul, 2011
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Some cosmos, such as C. atrosanguinus are tender perennials. The ones that are most commonly grown from seed are half hardy annuals. Each flower doesn't last all that long, but the plant produces more so it should still be flowering in autumn, provided it gets enough water, a bit of plant food and plenty of deadheading.
If your cosmos are going in the garden, I'd get them in there as soon as possible so that their roots can spread out and they get established. You could save seed for next year, but as they're native to Mexico none of them are hardy.
7 Jul, 2011