Maybe your soil is too good. Cosmos, in my experience, likes infertile, somewhat dry soil, and full sun. As I improved my beds, cosmos did worse and worse for me. Great big plants, gorgeous foliage--but hardly any flowers. I had to stop growing them and I love them.

I hear ya ginny, because i have seem them growingout of the cracks in sidewalks.Even when the parent plants , which i bought in a six pack last year were planted,i purposely didn't do anything with them.I was surprised to see them come up this year and have not touched them.It is getting so big and thick now that I think it will not flower.Couldn't STOP them from flowering last year.

I planted some from seed and made the mistake of using fertilizer after I planted. All I got was a big bushy plant, no flowers. The only plant I did not fertilize has flowers.

I agree, very dry soil and no fertilizer, and definetly the most sun you can give them.

Jen

Same here. I probably planted about 60 plants!! Really thick and lush looking foliage though.

tjsangel, that is what I did,but to no avail.Full southern exposure, dry soil, no fertilizer. I'm going to rip 'em out.

Another possibility is that since they reseeded, and weren't started early indoors, that they are late blooming for you...this happened to me a few times with reseeded cosmos...there's a chance yet before frost!

maureen1953, do they get real big beforethey bloom? I have stalks that are an inch thick.

There are all different varieties of cosmos, some bloom later than others, if that's the kind you have, there's still hope of bloom, even on hugh plants with thick stalks. The problem is, you and I live in short climate seasons, and by the time your's is ready to bloom, a frost might kill it. I'm guessing your's bloomed last year because you began with started plants already, not from seed. I could be wrong, but start looking for flower buds right about now, and if you're lucky you may see bloom before the winter!