I have several healthy clumps of this plant which have been in position in rockeries now for between 18 months and 2 years. I am not finding more than a single flower at the periphery of the clump when from reading the plant description it should be covered in blooms. Each clump has achieved its supposed spread of 30 ins.
Can someone please advise what might be the cause of this poor flowering in what should be an easy plant to grow?