I've had the same experience. One year I had cosmos plants that grew huge
but wouldn't flower. I tried adding flower fertilizer, Potassium something
I think it was, and breaking off the roots near the plant, but they would
not bloom.

I agree with the idea that the soil is too rich. When I first started my
garden and the soil was poor, cosmos flowered well. Now my soil is
enriched. However, the year mine wouldn't flower, I looked around the city
and saw other gardens in which the cosmos was flowering poorly, so I'm not
certain of my explanation, maybe it was just the weather.

"gregpresley" wrote in message
...
I haven't planted cosmos in several years. I planted the dwarf variety 3
years ago, and have just enjoyed the chance reseeding (the dwarf variety
seems to reseed a bit less prolifically than the taller varieties). This
year, I have many plants of various sizes, from 6 inches to about 2 feet
tall, all of which have been blooming for the past month or more -
however,
I have one plant which has a huge healthy central stalk, numerous strong
healthy branches, and not only no flowers, but not a single flower bud. It
is about 2 1/2 feet tall by now, less than a foot from other cosmos which
have been blooming for weeks. I would say that the central stalk on the
non-blooming cosmos is nearing 2 inches in diameter, and is practically
becoming woody. Since we sometimes have a killing frost in mid-September,
I'm starting to think that I won't see a single flower off that plant. Has
anyone else had that kind of a cosmos experience?