Whether you know it as rock rose, sun rose or Helianthemum, this small shrub offers colorful blooms, delicate foliage and drought-proof landscaping. One of its cultivars, Helianthemum nummularium Mutabile, blooms in several colors simultaneously. The bush grows about a foot high and 2 feet wide. Care for Helianthemum Mutabile is the same as that of other rock roses.
Siting the Plants
Helianthemums make excellent plants for the rock or xeriscape (low water) garden. Place Helianthemum Mutabile between small rocks, in front of larger ones, in front of foundations, or in the front of a perennial flower and shrub border. Hardy from zones 5 to 8, the shrubs may tolerate a zone 4 rock garden or cement foundation placement, due to the heat retention of the cement and rocks.
Preparing the Soil
Helianthemums prefer rocky or sandy soil. Consider lightening clay or normal soil with a bucket or two of sand or fine gravel, or both. This practice increases the drainage of the garden bed, which they need to prevent rotting or frozen roots in colder weather. The shrubs also prefer normal to alkaline soil. Have your soil tested by your local extension service or do it yourself with an inexpensive kit from the garden center. If the pH level registers below 7.0, add garden lime or wood ashes to increase the alkalinity.
Dig a hole at the depth to which the Helianthemum Mutabile shrubs were growing in the pot. If you haven’t lightened the entire bed with sand or gravel, refill the hole with an even mixture of garden soil and sand, or a soil and a sand/gravel mix. Tamp the soil down firmly and water well. If water seems to pool around the plants during watering or after a rainfall, dig up the Helianthemum and plant it on a low mound, slightly above ground level. It needs good drainage in order to survive the winter, especially in colder climates.
Watering and Feeding
Like the other Helianthemums, Mutabile is extremely drought tolerant. Water the shrubs only in times of severe drought, or if applying liquid fertilizer. During their flowering season, Helianthemums benefit from a feeding of liquid fertilizer made for flowering plants. Follow the directions of the package to determine the amount of fertilizer to use, and apply every three weeks.
Pruning and Mulching
After the shrubs blooms in late spring or early summer, remove the spent flowers and the tips of the flowering branches for better future growth. Every two to three years cut the branches back about 6 inches. Mulch the plants lightly during their growing season to suppress weeds, but add several extra inches in the winter to protect the vulnerable roots.
Divide Mutabile every four or five year to maintain vigorous growth. If the shrubs are brown and woody at the centers, cut off the side shoots, remove the spent center, and replant the shoots in several locations. Otherwise, use a knife of two sharp garden forks to divide the clumps in two.