Just pinch off the spent flowers and the seeds left behind in the old spent flowers - by not deadheading, you're letting all that energy go into seed production rather than into new branching and flowers.

Thanks duluthinbloomz4. I got like 4 lunch bags of future seeds.

My Cosmos has not even bloomed yet, am I getting too antsy? They are rather tall.

liz -- depends on when you planted them and what zone you are in.

Some cosmos planted here late June are just starting to bloom. Others that were volunteers are already blooming away.

They are faculative short day plants; if started outside in spring, they tend to flowering more as the days get shorter (under 14hours per day--which is just about now in zone 5).

Also possible to get them started earlier and then if they are mature enough by midsummer they will flower under the long days too.