Summer-flowering phloxes have had a rough time recently, partly because they are devilish to grow in a pot. When you see them on the garden centre bench, flowering reluctantly and with mildewed foliage, they tend to languish unsold and that’s not surprising. Nurseries avoid them, because they’re difficult to keep alive during winter in pots, so it’s hard to find a well-grown plant. This is a great pity because in good garden soil many are doughty stalwarts, providing fragrance and elegance to later summer borders. I tend to snap them up when and where I can. There’s a new Peacock series in garden centres, called Phlox paniculata ‘Peacock Purple’, and it’s an excellent performer.

If you doubt their garden value, or just want to be wooed by their sweet perfume, try to visit the phlox trial at RHS Wisley as soon as you can. Once autumn comes, the plants will be dug up for good because it’s the last year of a three-year trial which I have been helping to judge. It hasn’t been an easy trial. The bone-dry summer of 2011 saw then struggle to get established and mildew, a water-stress disease, set in. They rallied well for their second year, but 2012 ( the royal-barge wet summer) saw the flowers ruined by day after day deluges and cold weather. This year they are flourishing! In all there are 135 named phloxes on the RHS trial, mostly Phlox paniculata with some P. maculata (tighter heads, more lance-shaped foliage and spotted stems) and a few named forms of the hybrid P. x arendsii. The latter are very variable, but generally smaller-flowered. Phloxes were hugely popular in the first half of the twentieth century and Alan Bloom’s nursery listed three hundred in his 1939 catalogue. These would have been sent out mail order in autumn mostly, or in spring. Most have disappeared, although the salmon-pink ‘Eva Foerster’ (1934), which was on Bloom’s pre-war list, is still superb. Alan Bloom named several of his own after his Bressingham nursery colleagues. The deep-pink ‘Eva Cullum’ (1978 ) is by far the best of these and it has done extremely well on the trial. A later, lavender phlox was named after his favourite composer, ‘Franz Schubert’, in 1980. Again this has proved itself to be outstanding at RHS Wisley. If you’ve had trouble growing phloxes in your own garden I have always done well with ‘Monica Lyndon Bell’, even in drier places. This pale-pink phlox was found in a Hampshire garden owned by this lady in the 1970s and was first distributed by Bob Brown’s Cotswold Garden Flowers. (3ft/90cm) It has also proved itself as outstanding on the trial. The dark buds enhance the pale-pink flowers and the foliage is neat with emerald-green overtones. The old-fashioned airy white, ‘Alba Grandiflora’ and the mauve-flowered variegated ‘Norah Leigh’ are also good on drier soil.

Mostly though phloxes need moisture and deep soil. They also need space: they find it difficult to push through other plants. They’re shallow rooted and need to be kept well watered in dry spells. If they do get water-stressed, mildew often strikes. Some varieties are more prone than others. Although unsightly, mildew is not too harmful in the long run.

Ideally they should be divided every third year to retain vigour. Move them to a fresh site if possible. However variegated phloxes should not be moved as root disturbance can prompt reversion back to green leaf. Phloxes start into growth and emerge early in the year so most gardeners lift them in September, if dividing or moving, to allow them to settle. Feed them every spring using pelleted chicken manure, or Vitax Q4. The best mail order supplier — Special Perennials 01270 811443/ specialperennials.com