Posted: 23/09/2014 at 15:41
Have to agree with Lyn. Grow them as big as possible by potting on a few times and delay flowering by regular pinching out ( late June is fine for me)
However, they are annuals programmed to go over before autumn perennials and it is autumn. Not here in west Cornwall, of course You need to deadhead but cosmos will decidedly look tired now.
(no collapsing heleniums, dahlias, or salvias though.......my (infuriating) plug for preferring perennials )