Helianthemum nummularium [hee-lee-AN-thee-mum, num-ew-LAH-ree-um] commonly known as rock rose belongs to the Cistaceae family.
Another common name of the plant “flower of the sun” comes from Greek words helios meaning “the sun” and anthemon meaning “a flower.”
Besides the beautiful showy flowers, the plant is loved for its charming green-grey evergreen foliage which looks stunning among other flowering plants.
Helianthemum Nummularium Care
Size & Growth
Under the right growing conditions, the rock rose takes height at a fast rate.
Once planted in its permanent place, the roots take hold fast and grow relatively quickly.
The plant is prostrating, meaning it’s low-growing and stays close to the soil.
At most, the plant can grow up to 12” inches in height.
However, it has a respectable spread and covers around 24” – 36” inches of space.
This is why gardeners prefer using the rockrose as a ground cover plant in garden beds.
Flowering and Fragrance
The varying shades of orange, pink, white, and yellow of this plant makes it a favorite among gardening lovers.
The showy blooms are full during the spring and early summer.
Garden beds and boundaries all come alive when the masses of saucer-shaped flowers open up.
Unfortunately, the flowers open only for a day when the sun is shining.
On the other hand, it does flower profusely, meaning new buds keep opening up for at least two months.
While the flowers don’t have a specific fragrance, it does attract insects like bees and some species of small beetles.
Light & Temperature
The plant is not particularly tolerant of very hot temperatures.
It thrives in areas where the summers are cool, and winters are relatively warm.
Being a native to Europe, it is used to temperatures included within USDA zones 5a to 8b.
However, you need to keep an eye on the plants if you live in USDA zone 5.
While it does have chances of growing, hardiness is not 100% reliable.
Watering and Feeding
Rock rose plants prefer dry to moderately moist soils.
Overwatering and using soil with poor drainage easily leads to root rot.
When watering, check the soil with your finger and make sure it’s not too wet.
Be extra careful when temperatures start going down.
As for feeding, you don’t need to add fertilizer or compost as the plant is self-fertile.
If the soil becomes too rich, it will cause growth to become leggy, which does not look good and requires replanting.
Soil & Transplanting
The common rock rose is a bit choosy when it comes to soil.
It does best in sandy or rocky soil.
However, it is also suitable for loamy, chalky, clay, and sandy soils.
It also bears alkaline, neutral, and alkaline pH, but prefers alkaline to neutral soil.
The soil must be well-drained.
If it doesn’t have good drainage, excessive water will surround the soil too long, which leads to root rot, which is bad for overall growth.
One important thing to remember about the plant is its dislike of root disturbance.
Once the roots have been established in the permanent location, moving the plants leads to failed transplanting.
When you’re propagating new plants, whether from seeds or cuttings, you need to transplant them before the roots embed themselves well.
Grooming and Maintenance
Like other evergreen subshrubs, this plant is low-maintenance.
Since it’s mostly grown as a ground cover, pruning is not necessary.
However, shearing is encouraged during mid to late spring.
Once the plant has flowered, shear back the growth to give shape to the spread and to promote new growth extending the life of the plant itself.
How To Propagate Rock Rose
The rock rose is propagated two ways:
Seeding is done in the fall.
- Sow them in individual starter pots.
- Germination does not take long.
- Once the seedlings are strong and long enough to be handled, transplant them to individual pots or their permanent as soon as possible.
Softwood cuttings are done in late spring or early summer.
It’s better to sow the cuttings in their permanent locations as the plant despises being transplanted.
Flower Of The Sun Pest or Diseases
The plant is typically pest and disease-free. They’re known for their resilience to honey fungus.
However, you need to be careful when watering the plant.
If the soil is sufficiently moist, don’t overwater.
Too much water is not tolerated well by the plant and ends in root rot.
Helianthemum Rockrose Uses
Growing in a prostrate position, the rock rose is perfect for ground coverage.
Use the plant in between other perennials or flowering plants to cover exposed ground.
Besides the ground cover, the plant is an excellent choice for rock gardens (it’s in the name!), coastal gardens, and cottage gardens.
It looks beautiful used as an edging or border plant and placed around border fronts or on stone walls to create a cascading effect.