too much of the wrong fertilizer .. too much nitro means lush vegetative growth.. and little or no flowers...

too much nitro also translates into HOT manure ... instead of aged 'nure...

jsut a guess .. ken

Some cosmos plants take all summer to bloom. They are oddballs. But when they do bloom, you will have 100 flowers on one plant. I used to pull them out, thinking they were non-flowering mutants, but now I wait for the show. Some of them grow to seven feet before bursting into bloom. Keep them staked or tied up because a good storm will topple them. It's worth the work.

Just as a follow up to this question, I want to tell you that my cosmos are in full bloom right now!
Thank you Susan for giving me hope so that I did not pull them out!

Originally, garden cosmos were like mums in that they needed long days (technically short nights) to initiate flower buds. Breeders selected for day neutral plants and so they bloomed all summer long. There are a few cultivars that are day length sensitive so you sort of have to do your research before you buy seeds.

Strange....we were just going over SD, LD and DN plants in greenhouse mangangement last thursday (we, the students are growing over 1000 Poinsettia crops :)
Anyhoo, I put out C. bippenatus this spring...most began bloom early summer thru fall and just one in the group has refused...I let it go until this weekend and finally pulled it. Maybe I should have waited...some genetic mutation to SD bloom maybe?

Thanks for education Happyhoe...something I can bring up in class and look smart LOL LOL!

Vera