ROCK roses, or helianthemums, have been in flower in recent weeks and their colourful spreads make a great impact on the garden in early summer.
The plant is a small shrub with wiry stems that carry a cluster of pretty, open flowers. It is a native plant, growing in the dry rocky soil of the Burren in Co Clare, and in mountainous areas in Europe.
It is called rock rose because it grows in rocky places and because the flowers are like small single roses, rounded, flat or cup-shaped and with a boss of yellow stamens at the centre.
The plant loves a sunny spot in well-drained soil, but it needs to root down deeply and does not thrive if the soil is shallow or very dry.
In heavy soil, the little shrub tends to grow very soft and often dies from root rot disease. Although rock roses are alpine plants, they tend to be too large for a small rock garden, but look really well tumbling over a low wall or bank.
Rock rose can reach over a metre in diameter, making a low spreading bush covered with flowers. Being a shrub, though its woody stems are very slight, and given the right conditions, it can live for many years and gives excellent value with a superb initial rush of flowers, followed by a scattering of blooms later.
The wild rock rose has bright deep yellow flowers but there has been a lot of cross-breeding carried out by nurserymen to give a wide range of varieties, mostly in shades of yellow, orange, red, pink and white.
In general, rock roses have green leaves and are semi-evergreen, but some have grey-green leaves, such as the lovely 'Rhodanthe Carneum' with soft pink flowers over grey foliage.
'Wisley Pink' is pale pink and 'Wisley Primrose' is pale yellow, also over greyish leaves. 'Ben Fhada' is bright yellow and 'Ben Ledi' is bright crimson red. 'Fire Dragon' has a red centre and orange outer petals. 'Cornish Cream' is pale cream-yellow. 'Ben Hope' is a bright pink form.
Some kinds have double flowers, such as the lovely 'Cerise Queen' and 'Jubilee' which is bright yellow. 'The Bride' is white with a soft yellow centre.
The soft pastel shades and the hard bright colours do not always sit happily together and it is best to choose varieties in flower to suit their use in the garden and how they can be worked into existing colour schemes.
The flowers close on a dull day and this prolongs their flowering.