Posted: 25/05/2012 at 22:30
I've got clay soil and I have several plants that bloom Aug/sept. I love my heliopsis, tall yellow daisy flowers.Like to spread so keep it under control, but it will bloom for a good 8-9 weeks. Valerian, michaelmas daisy, marigolds, golden rod, gaillardia, all seem to love the clay. A favourite is Hypericum 'Magical red star' has pretty yellow flowers which fade and scarlet red berries follow, so the colour goes on for ages.
Hope I've been some help. I keep a diary of whats flowering and when, so I can see at a glance when plants are at their best,