I have volunteers for the second year from Sonata Pink. One group of three bloomed one month. Others keep coming up and will keep the bloom going until frost. Some are reverting to taller plants, so I will buy fresh seed next year. They are short-day plants so bloom later in the season than some annuals.

I had one last year grow eight feet tall and never bloomed.

Cosmos does not like rich soil or it will grow too many leaves at the expense of blooms. Don't feed it much. Just water. It'll will bloom for a long time.

true, I planted my seeds in clay, very little fertilizer when they started to get about 1ft tall, and made sure to cut them to encourage more flowers; they are now about 6ft tall. I just need to know what to do with them at the end of the season ?