In two different years now I have purchased cosmos plants to start in my flower garden. They grow huge but never flower. They get about 4-5 hours of sunlight a day. Anybody got any ideas why.
The blind leading the blind... at least you can get them to grow green... I've tried starting them from seed and not a single plant germinated. :o/
Cosmos likes lean soil. Your garden soil must be rich in nutrients, especially Nitrogen; that's why your Cosmos is growing huge and green. :-)
I second the N comments above. Cosmos is one of the flowers I interplant with my vegetables to attract pollinators. When I used to fertilize heavily, the plants would actually _stop_ blooming (I was using transplants) and become green & bushy. They would eventually bloom heavily, in late summer.
Now, with organic methods in a new plot, they are blossoming continuously.
I plant cosmos in the gravel that covers our septic tank, which has to be dug up every few years. It blooms fine there and even drops seeds, which bloom in following years.