Q. What is a rock garden plant?
A. Anything which will grow well and fit into a rock garden situation.
There are few limits to what you can put on a rock garden if you want to. In fact size may be the only limiting factor, so there’s a whole host of opportunities.
In South Africa, I’ve seen Agapanthus praecox AGM and Kniphofia northiae AGM romping away on lower mountain slopes amongst the rocks. In the UK, though, these plants grow really well in a sunny border, so why not use your rock garden for some plant gems which are more choosy about their conditions and which may get lost amongst bigger garden plants?
Rock gardens create a niche habitat, providing crevices and pockets into which small and unusual plants can be grown. Rocks can provide shelter from winds, and small free-draining pockets which allow plants which resent waterlogging to survive the winter wet.
Even a small rock garden or crevice garden can provide a range of small microclimates in your garden. In fact the more variety in terms of size and aspect of crevices the wider your choice becomes.
I love to fill the cracks in between the rocks with houseleeks (Sempervivum) and Saxifraga paniculata. This resembles their natural habitat and allows them to grow with less competition from other plants. Campanulas and aubrietia also make good crevice plants but beware - some can be quite rampant and self-seed everywhere.
To provide structure, add in some small shrubs like rock roses (Helianthemum), Hypericum olympicum AGM and Daphne × susannae. There are also some lovely dwarf conifers available from plant centres such as Cryptomeria japonica ‘Vilmoriniana’ AGM, which is globose in habit and has a beautiful red tinge to its foliage, providing wonderful winter interest. If you like to cook, try adding herbs to your rock garden. Thyme, rosemary and oregano fit perfectly into a rock garden situation and also provide a wonderful fragrance.
Many typical rock garden plants enjoy a sunny position but there are plants for shadier situations. Cyclamen hederifolium AGM (autumn flowering) or Cyclamen coum AGM (spring flowering) are wonderful pockets of colour at the beginning and end of the year.
Additionally, saxifrages often enjoy a shadier spot. Early-flowering perennials such as winter aconites or snowdrops can be planted under conifers or small trees and shrubs and provide late winter colour. They’re really pretty – uplifting and inspiring just when we need it most.
At Wisley we are currently redeveloping the planting on our north-facing rock garden and the alpine team are having great fun trying to use all the niches, sun pockets and shadier areas to their greatest effect. Planting will start in April and continue in the autumn and the following spring - so if you are at Wisley come and follow our progress in this exciting project.
Find out more about rock gardening
Visit the RHS London Alpine Garden Show (26 April)