Helianthemum (Rock Rose)
Common name: Rock rose
Among my lasting garden memories is a sunny early summer morning and coming across a large rock bank planted entirely with helianthemums, widely known as rock. The numerous plants provided a fantastic kaleidoscope of colour. Helianthemums are no strangers to our gardens, and are currently enjoying a well-deserved surge in popularity. These are easy-to-grow shrubs and will thrive in even quite poor conditions. They are ideal for an open pocket on the rock garden or for edging the border.
Those most widely available are hybrids with single or double. There is considerable variation in both leaf and flower colour, the latter including crimson, pink, flame, a lovely coppery orange, bright yellow and white. Individual blooms last for only one day but there is no need to worry as next morning new flowers will open. This goes on for several weeks. The singles retain their petals for a longer time than the doubles.
Popular species and varieties
In any list of helianthemums you will come across varieties with the ‘Ben’ prefix. These are old stagers having stood the test of time well. Among the most popular is ‘Ben Fhada’, its yellow, orange-centred flowers contrast well against the dark green foliage. ‘Ben Hacklar’ is a vigorous plant with large copper-orange blooms over rich green leaves. ‘Ben Ledi’ has narrow leaves and flowers of a deep wine red. One not to overlook in this series is ‘Ben Nevis’ with a plentiful supply of tawny orange-yellow flowers.
The Royal Horticultural Society’s Award of Garden Merit is currently held by seven varieties. One of these is ‘Fire Dragon’, with vivid orange-red flowers over grey-green foliage. Others holding this award include ‘Amy Baring’, noted for its profusion of rich golden yellow blooms, and ‘Henfield Brilliant’, a spreading plant that, in late spring and early summer, is almost hidden beneath a mass of eye-catching flowers in vivid brick red.
Two others with single blooms are ‘Rhodanthe Carneum’, which can sometimes still be found listed under its old name of ‘Wisley Pink’. An old favourite, ‘Wisley Primrose’ is a spreading shrub with grey-green foliage and masses of lovely pale primrose flowers.
Two award holders with double blooms are ‘Jubilee’ which produces a fine show of sulphur-yellow flowers, and the equally attractive brick-red ‘Mrs. C. W. Earle’, the blooms of which are held clear of the dark green leaves.
‘Coppernob’ has deep orange blooms, each with a dark red centre. Another that should not be overlooked is ‘Wisley White’ with masses of single blooms. Look out also for ‘The Bride’; its flowers have a rather interesting white papery texture.
For those who like something different then ‘Raspberry Ripple’ with cream and dark pink flowers is worth considering,’Chocolate Blotch’ is also popular, the buff-coloured blooms have a distinctive chocolate brown blotch at the base of the petals. One with a low-growing habit, reaching just 20cm (8in) in height, is ‘Fireball’ with lovely dark red flowers contrasting well against the foliage.
Soil type Light, well-drained, rather poor soils.
Planting These are sun lovers, and if planted in full sun they will flower profusely. Plant in the autumn or spring. Allow plenty of space as some varieties spread to 60-90cm (24-36in). Choose a selection of colours if planting on a bank, or alternatively select just one variety, which will have a very dramatic effect.
Maintenance When flowering has finished trim the plants with a pair of shears; this will keep them tidy, encourage new growth, and often a further flush of flowers later in the season.
Propagation Helianthemums are not long-living plants so it is a good plan to keep youngsters coming along. Increase stock by taking cuttings with a heel in early or mid-summer. Take the material from non-flowering shoots.
Pests and diseases Generally, these shrubs are not troubled by pests. A fungal disease can cause stems to collapse. In bad cases lift and burn the affected plants.