Helianthemum nummularium subsp. grandiflorum
Common Name: rock rose
Type: Herbaceous perennial
Family: Cistaceae
Native Range: Central and southeastern Europe
Zone: 6 to 8
Height: 0.50 to 1.00 feet
Spread: 1.00 to 3.00 feet
Bloom Time: May to June
Bloom Description: Yellow
Sun: Full sun
Water: Dry
Maintenance: Medium
Suggested Use: Ground Cover, Naturalize
Flower: Showy
Tolerate: Drought

Culture

Best grown in dry, alkaline, rocky or sandy, well-drained loams in full sun. Foliage is evergreeen, but plants are not reliably winter hardy throughout USDA Zone 5 where they appreciate a winter mulch (preferably a cover of evergreen boughs). Plants prefer cool summers and warm winters, which makes them less than ideally suited for the St. Louis climate. Shear plants after flowering to shape and to encourage additional growth. If grown as a ground cover, space 2-3’ apart.

Noteworthy Characteristics

Helianthemum nummularium, commonly called sun rose, is a low-growing, woody-stemmed, shrub-like plant with evergreen foliage. It typically grows 8-12” tall and spreads by creeping stems to 3’ wide. Five-petaled, rose-like flowers (to 1” diameter) bloom for up to 2 months (late spring to early summer) in terminal cymes. Flowers have somewhat variable coloration, but most often feature pastel yellows and pinks. Each flower opens for only one day, but in the proper growing environment, bloom can be so profuse as to cover the entire plant to the point of obscuring the foliage. Grayish-green, lance-shaped leaves (1-2” long).

Subsp. grandiflorum primarily differs from the straight species by producing slightly larger flowers (grandiflorum meaning with large flower) to 1 1/2” diameter in colors of golden-yellow to orange. Leaves are sparsely pubescent beneath. It is native to alpine areas of central and southern Europe including the Pyrenees, the Carpathians and the Caucasus.

Genus name comes from the Greek words helios meaning the sun and anthemon meaning meaning a flower.

Specific epithet means resembling a coin.

Problems

No serious insect or disease problems. Rots easily in poorly-drained soils.

Garden Uses

Rock gardens, borders and ground cover. Sprawls exceedingly well over stone walls or dry, sloping ground.