|Official Plant Name||Helianthemum|
|Common Name(s)||Rock Rose|
|Native Area||Europe, South-West Asia|
|When To Sow||May, June, July, August, September|
|Flowering Months||June, July, August, September|
Exposed or Sheltered
0.1 – 0.5M
0.1 – 0.5M
May – September
Most soil types
Moist but well-drained or well-drained
Only about a foot high, Rock Rose shrubs offer advantages few plants of that size do.
It is a no-care option that gets by in conditions that other flowering plants wither in – poor soil, aridity, and sea-spray are as if nothing.
It provides year-round low-growing foliage of a cool green hue and oodles and oodles of simply delightful flowers from pastel yellow to ruby red.
About Rock Rose
Helianthemum is a genus of 100 to 110 low-growing evergreen shrubs and subshrubs plus a few herbs that inhabit Europe, Northern Africa, and South-Western Asia.
Members of this genus grow in numerous and varied habitats from oceanside cliffs to interior grasslands, and from highland meadows to rocky barrens.
Helianthemum nummularium cultivars are spreading, mat-forming evergreens that are as if tailor-made for specific garden purposes like floral designs, groundcover, rock gardens, and low edging.
Helianthemum is probably more widely known to and more extensively used by professional landscapers and institutional gardeners than the general public and home gardeners.
Those Helianthemum species that have ornamental value and all of the cultivars are also formally named ‘Rock Rose’ though the genus as a whole with all its species is also sometimes informally referred to as Rock Rose.
Be aware that – very confusingly – the related genus Cistus is also sometimes called Rock Rose.
These spreading shrubs and subshrubs grow from about 20 centimetres to 50 centimetres. Barring a few exceptions, all of the in-demand varieties reach heights of 25 to 35 centimetres.
Foliage and Flowers
This little plant’s small leaves are opposite; on some species the upper stems’ leaves are alternate.
In the majority of varieties the foliage is a subdued but coolly attractive greyish-green or bluish-green shade. Because of this tone and texture of the foliage, these plants are also called Frostwort.
Interestingly, the shape of the leaves varies quite a bit even among the cultivars, varying from linear to ovate with the majority being lanceolate or elliptic.
The arrangement of the flowers varies by species. They may be single or borne in some or another type of inflorescence.
In Helianthemum nummularium and its cultivars, the flowers are single or are borne in loose terminal clusters. Flowers are always five-petalled and are disk-shaped or saucer-shaped, and 2.5 to 3 centimetres wide.
Their colours include white and span the warm spectrum from light yellow through ruby red and they often have an eye or central disk.
They are delightfully pretty and though the blooms last for but a day, the shrubs are incredibly prolific. Rock Rose plants typically bloom from late spring to midsummer, and profusely at that.
The desirable varieties of Helianthemum are cultivated and grown in an increasing number of countries and are rising in popularity; indeed, eight of these little flowering shrubs have even been awarded the RHS’s Award of Garden Merit.
But the realities could not be more different and more grim for the less well-known species – would you believe that some are on the road to extinction?
H. songaricum and H. ordosicum are native to hilly regions of Southwestern China. Human settlements in their habitats and resultant habitat-altering activities, such as agriculture and grazing, have severely fragmented these species’ populations which have been declining for several years. This led to both species being categorised as ‘Endangered’ in the China Species Red List.
H. marifolium and H. caput-felis grow in the islands, cliffs, and coastal regions of the Western Mediterranean region. Their habitats have been disturbed and even taken over by tourist resorts and urban sprawl. H. marifolium is termed ‘Vulnerable’ and H. caput-felis ‘Rare’ and both are categorised as ‘Endangered.’ Each species has been accorded a protected status under the respective country or region’s laws.
No matter which varieties you choose to grow – the endangered ones or the AGM ones – these mat-forming evergreens that bear exceedingly pretty flowers over a long blooming season are truly no-care no-fuss plants that will bring their own unique charms to your garden.
Background and Origins
Helianthemum evolved and diversified during the Pleistocene Epoch during the time that early humans made their debuts.
This diversification occurred in the Mediterranean and the nearby subdesert regions; as such, it is not surprising that the Mediterranean is the locus of this genus’s greatest diversity.
Helianthemum species and certain fungi are often found as symbiots. These plants and edible desert truffles of the Mediterranean and Middle East are well known to occur in ectomycorrhizal association in arid ground.
Helianthemum plants serve as markers for truffle hunters.
Helianthemum nummularium has undergone significant floriculture in England with the result that a few double flowers have also been developed. One can choose from a total of 200-plus cultivars in a wide range of hues and tones spanning the entire warm spectrum plus white.
The plant’s name derives from the Greek word ‘helios’ for sun and ‘anthemon’ for flower, which alludes to the sunny yellow hue of Helianthemum nummularium blooms.
H. apenninum or White Rock Rose has linear to lanceolate leaves and produces snow-white flowers with a yellow central disk and stamens to match. This species can reach a height of 50 centimetres.
H. nummularium or Common Rock Rose is the species from which the vast majority of cultivars have been developed. It attains a height of 30 to 40 centimetres. It has oval leaves and bright yellow flowers with prominent orange stamens.
The following selected cultivars typically bloom from late spring to the middle of summer though you can try to extend the blooming season by trying the two suggestions outlined in sections Feeding, Care and Growing Tips and Pruning Rock Rose. They reach heights of 25 to 35 centimetres.
‘David’ has lanceolate leaves and a pure white flower with sizeable central disks and visible buttery stamens.
‘The Bride’ has foliage that is distinctly silvery-green with a frosted appearance while the flowers are white or off-white with yellow eyes. RHS Award of Garden Merit.
‘Wisley Primrose’ has greyish-green lanceolate leaves and produces classic primrose yellow flowers with darker, buttery yellow centres. RHS Award of Garden Merit.
‘Jubilee’ is one of the few varieties to produce double flowers; these are of a primrose yellow hue. RHS Award of Garden Merit.
‘Ben Attow’ has dark green lanceolate leaves and produces lemon yellow flowers with prominent matching stamens.
‘Praecox’ has chalky-green lanceolate leaves and bears flowers that are fully yellow of a bright, sunny hue.
‘Marianne’ has greyish-green pinnate leaves and bears whitish flowers that have a faint pink tinge or pink flush set off by bright yellow stamens.
‘Orchard’s Medius Pink’ has appealing light green leaves and bears baby pink flowers with sizeable central disks in orange which are further centred by bright yellow stamens.
‘Rose Queen’ has elliptic leaves of a greyish-green hue and bears soft pink flowers with golden eyes and prominent stamens.
‘Rhodanthe Carneum’ has silvery-grey elliptic leaves and bears soft pink flowers with yellow centres further accented by yellow stamens. RHS Award of Garden Merit.
‘Ben Lomond’ has dark green elliptic leaves and produces flowers of a classic baby pink hue that have prominent golden stamens.
‘Georgeham’ has greyish-green lanceolate leaves and bears bright pink flowers with a creamy pink disk further centred by prominent yellow stamens.
‘Highdown Apricot’ has greyish-green leaves with flowers of an unusual pastel apricot-pink hue with a bright yellow central disks and visible yellow stamens.
‘Honeymoon’ has bright green elliptic leaves and produces peach to light orange flowers with prominent yellow stamens.
‘Orchard’s Dwarf Orange’ has light green elliptic leaves and bears flowers of a rich amber-orange with prominent yellow stamens.
‘Henfield Brilliant’ has lanceolate leaves of a frosted greyish-green hue and produces poppy orange flowers with visible yellow stamens. RHS Award of Garden Merit.
‘Ben Heckla’ has grey-green ovate leaves and bears rich orange flowers with large vermilion central disks with just-visible yellow stamens.
‘Alice Howorth’ has mid-green pinnate leaves and bears flowers that are of a chalky coral tone and red at the centres with prominent yellow stamens.
‘Orchard’s Griseo’ has bright green pinnate leaves and bears coral pink flowers with very prominent buttery yellow stamens.
‘Dompfaff’ has dark green pinnate leaves and produces flowers of a chalky lipstick-red hue which are darker at the centres and have prominent yellow stamens.
‘Orchard’s Pastel’ has cool green lanceolate leaves and produces rose-red flowers with prominent yellow stamens.
‘Cerise Queen’ is one of the few varieties to produce double flowers; these are of a saturated pinkish red or lipstick red hue.
‘Orchard’s Royale’ has silvery-green lanceolate leaves and bears fuschia to magenta-toned flowers with bright yellow stamens.
‘Fire Dragon’ has bright green lanceolate leaves and bears scarlet flowers with a deeper red centre and visible yellow stamens. RHS Award of Garden Merit.
‘Beech Park Red’ has elliptic dark green leaves and produces bright red flowers with visible yellow stamens.
Habitat and Growing Conditions
These plants almost always grow in sunny locations, and most are lime-loving plants that grow well in chalky, calcareous soils.
Apart from these two common factors they grow in semi-desert, grassland, field, hilly, and coastal locations.
None of the species or cultivars need fertile soil and in nature the species frequently grow in even stony and gravelly ground.
All the desirable varieties are hardy to Zone H4, making them just hardy enough for almost the entire United Kingdom.
Where to Plant Rock Rose
The very name Rock Rose is an indicator of where you can plant this tough but delightful shrub. It can make do in poor, gravelly or stony soil, and it is one of the best choices for rock gardens.
These shrubs are perfect for narrow borders where you want low-growing plants. Any strips of indifferent soil, such as between a walkway and a dwelling’s wall, or between a driveway and a tiled courtyard, can be greened (and flowered) wonderfully well by Rock Rose varieties.
Rock Rose varieties are excellent choices for groundcover on barren slopes and verges where the spreading mats will both control erosion and provide all-year greenery.
In coastal locations that are windswept, have salt-sea air, and sandy ground where you will be hard-pressed to grow any flowering plants, Helianthemum will prove to be a godsend.
Lastly, you can grow this plant between paving slabs and stones, and between paving slabs and bordering concrete to control erosion, crumbling, and to hold the ground and slabs together.
Feeding, Care and Growing Tips
The only no-nos for Helianthemum are heavy clay soils and acidic soils, and full shade. Other than that, anything goes.
Even though this is a lime-loving genus do not plant it in heavy clay soils. Indifferent soil is fine so long as it is alkaline. If you have chalky soil and want to plant Rock Rose, you are in luck.
A light, friable soil made up of gravel, sand, and chalk amended with just a little organic compost or humus will work out very well for all Helianthemum.
They do not care for rich soils. The soil pH may be from Neutral to Moderately Alkaline – 6.6 to 8.4. Soil must drain well and should not stay damp.
The location should offer full sun or at least partial sun.
Growing From Seed
Helianthemum can be grown from seed.
This can be done indoors at the break of spring for transplanting outdoors in late spring, or the seeds can be sown directly outdoors in late spring which is the more straightforward option.
Scarify and soak about half your seeds before sowing. Sow seeds on the surface and very lightly cover them with a sprinkling of soil.
Water them well and keep watering frequently. They usually take 15 to 20 days to germinate.
Gradually reduce the amount and frequency of watering as the plants grow. After they have matured they should be watered only when the soil dries out.
As a guideline, about one centimetre of water twice a week should be enough.
In the country’s colder regions it would be wise to mulch Helianthemums.
Fertilising is not needed but if you would like to try to boost the number of blooms over the season or its length, you can feed the plants once in mid-spring using a small amount of 5-20-10 liquid fertiliser.
Do not use a balanced fertiliser or one meant for ericaceous plants.
Pruning Rock Rose
Rock Rose does not need any pruning. However, you may prune them for two reasons.
If you want the plants to stay close to the ground and form a mat-like groundcover, you can prune old woody stems in early spring.
In favourable climates, you may be able to stimulate a second bloom in late summer or early autumn by cutting back the shrubs by about a third.
Rock Rose is not known to suffer from any pests or diseases.
Where to Buy Rock Rose
For those in the know and for professional landscapers, Rock Rose has long been a plant of choice but in decades past it was not easily available to home gardeners.
However, as it gains a higher profile and becomes a popular shrub, more and more nurseries are stocking at least a few different varieties.
Even if you don’t find them at a nursery in your town, you can get quite a variety of Helianthemum from online merchants.
Kersie learnt the basics of gardening as a toddler, courtesy of his grandfather. In his youth he was an active gardener with a preference for flowering plants. He is a professional and vocational writer and his freelance projects have spanned various kinds of writing.