ROCK gardens are traditionally spring features, but, with careful planning, colour and interest can be spread right across the seasons. At this time of the year, continuing value can be obtained by carefully selecting choice flower and foliage plants.

Although having year-round attributes, dwarf conifers are an important part of the summer rock garden. Their fresh growth is often at its most lustrous during July and August, and they provide a lovely foil for flowering plants.

Most of the finest summer flowering plants come from North America. Beautiful creeping phlox and colourful penstemons which blossom for several weeks and are available in a wide array of colours.

The rock garden phlox are typified by the cushion phlox, a lovely lavender-flowered scrambler which makes an excellent companion for the strongly fragrant white, pink or bluish Douglas phlox.

Look out for the magenta Crackerjack, bright red Tycoon and soft lavender Eva. Penstemons make a very important contribution to the rock garden. While often regarded as tender, the majority pass through the winter unscathed if planted in a free-draining medium.

They are available in a wide variety of shapes and colours, but the mountain pride penstemon, with its bright blue tubular blossoms, and the pin-leafed penstemon, sporting needle-like foliage and orange-red flowers, are amongst the easiest to grow.

All the alpine pinks are of reasonable temperament, although they prefer alkaline conditions. The maiden pink and its varieties, Flashing Light and Brilliancy, are amongst the most spectacular, but the sand pink has a simplicity which appeals to all.

The best range is amongst the true alpine pinks or Dianthus alpinus. This has given rise to a wide variety of colours from white and soft pink to crimson with various colour combinations and zonings as well.

Campanulas are almost as diverse as pinks. These are the tiny bell flowers in blue or white typified by the tussock bell flower and fairy thimbles, two extremely free-flowering scrambling species.

If your rock garden is looking rather dowdy, get down to your garden centre and select one or two of the very many summer flowering varieties of alpine plants that are available. You can plant them now in full flower for instant impact.

WHAT'S NEW

Helianthus Terracotta is a tall brownish-orange coloured sunflower which does not produce pollen.

Flair is the latest hypericum variety which produces yellow flowers for cutting followed by coral berries.

Cocostem is a plant support system which enables a hanging garden to be created from potted plants.

Q There are strange tunnels in the leaves of my chrysanthemums. What has caused them, and how can I control the problem?

A The tunnels are caused by the grub of the leaf miner. They can be controlled by the regular use of a systemic insecticide.

Q The ends of my tomato fruits are going brown and rotten. What is the cause?

A Your tomatoes are suffering from blossom end rot because of irregular watering.