Posted: 24/05/2015 at 22:00
Hang on folks. Don't chop for the sake of it.
i cut back hardy geraniums ....some of them.....in mid summer when the fullest flush of flowers is fading. A trim back...not really a "Chelsea chop"......and they will flower anew a few weeks later. This isn't to keep them bushy but to re energise flowering.
Some plants benefit from being chopped back now and others don't.. don't think it will make much difference to asters.
best thing is to watch how your plants grow and learn...some benefit from chelsea chop, some from pimching back, others trimmed, others need staking.