How do I fix phlox?

GARDENING TIPS

- Anne Swithinbank

Q Over the past few years, we’ve planted different varieties of phlox into mixed borders. The plants seem to have shrunk and make one or two spindly stems with few flowers. How do we encourage a proper show? Meg Duncroft, Doncaster, South Yorks.

A There are alpine phlox, dainty semi-evergreen blue phlox (cultivars of P. divaricata) and annual phlox (P. drummondii), but I think we are dealing here with cultivars of the herbaceous perennial Phlox paniculata. These fragrant phloxes are the best known of their group and should make generous clumps of fluttering flowers around 3ft (1m) tall and at their best from July-September. Their tall straight stems are great for cutting, making them a favourite florist’s flower for summer bouquets. The species is native to eastern parts of the USA, usually from riverside habitats, and while our cultivated forms are straightforward to grow, they are particular in their needs.