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Helianthemum - Growing Guide
Rock rose, Sun rose
Rock roses are low growing evergreen shrubs or sub-shrubs which mainly originate from the Mediterranean regions. As such they need a hot sunny spot. Ideally this might be on a southern facing slope fully exposed to the sun. The flowers open sluggishly or not at all in dull weather. The individual flowers last only a day and are best in the mornings as some varieties tend to close up at midday. Nevertheless the flowers appear in extraordinary profusion and each day’s crop is succeeded by an entirely different one on the next.
Apart from their smaller size the difference between Helianthemum and Cistus is that their seed capsules have three valves whereas Cistus have five, six or more separate seed valves.
Helianthemum are perfectly suited to rock gardens. Some of the wild growing species thrive on limestone so a neutral to alkaline soil is perfect if it is well drained. If you do grow them as groundcover or as edging to the herbaceous border be careful to avoid any contact with fertiliser or improved acidic soils. Crevices within a patio or holes in walling with some soil are equally good places to site these small but impressive plants.
A light pruning after flowering is over (perhaps in mid-July) is advisable to shape these plants and encourage them into a second less significant flowering later in the summer. Young plants which grow on well in their first year will however need little initial attention and will probably produce a second crop of flowers anyway.
The choice of which named varieties of Helianthemum to grow can be determined partly by colour:
H. ‘Wisley Pink’ has silver-grey leaves and pale pink flowers flushed yellow in the centres. This is a more robust spreading shrub than other varieties.
H. ‘Wisley Primrose’ has grey green leaves and pale primrose yellow flowers
H. ‘Ben Fhada’ is a strong yellow with a contrasting orange eye
H. ‘Ben Ledi’ has dark green foliage and is a deep rose colour
H. ‘Ben More’ has glossy foliage and flame orange flowers
It is quickly obvious that these plants look good when mixed together in groups. None grow more than 12in high with a similar sort of spread.