Calandrinia spectabilis, commonly known as Rock Purslane or Red Moondust, is a low-maintenance, shrubby succulent. Valued for its persistent, vivid blooms, the plant features fleshy, blue-green leaves that form a dense rosette. Thin, wiry stems carry masses of bright magenta or purple, poppy-like flowers that open with the sun, creating a striking cloud of color from spring through fall.
Optimal Growing Conditions
Rock Purslane thrives in full sun, which supports its long flowering season and compact, succulent growth habit. In regions with intense summer heat, the plant benefits from afternoon shade to prevent scorching or stress, which can slow growth and flowering.
As a succulent, Calandrinia spectabilis requires soil that drains rapidly. Planting in heavy clay or areas prone to water retention quickly leads to root rot and plant failure. The ideal substrate is a sandy, gritty, or rocky mix, mimicking its native arid conditions. Incorporating pumice or perlite improves aeration and drainage.
This frost-tender perennial performs best in USDA hardiness zones 8 through 10, withstanding temperatures down to about 20°F to 25°F. Outside of these mild climates, it is cultivated as an annual or grown in containers moved indoors for winter protection. Its natural heat tolerance makes it an excellent choice for xeriscaping or rock gardens.
Watering and Nutrient Requirements
Rock Purslane is highly drought-tolerant once established because it stores water in its fleshy leaves. This makes it far more susceptible to overwatering than underwatering, which is the most common cause of decline. Water deeply and thoroughly, then allow the soil to dry out completely before the next application.
Watering frequency will differ based on the planting location; in-ground plants require less frequent supplemental water, while container plants dry out faster and may need water weekly, especially during heat waves. Regardless of the setting, the goal is to fully saturate the root zone and ensure that excess water can escape immediately, never allowing the plant to sit in wet soil.
Rock Purslane has low nutrient requirements, reflecting its ability to thrive in poor or rocky soils. If established in soil amended with compost, it may not require additional feeding to support its growth and bloom cycle. If growth seems slow, apply a single application of balanced, diluted liquid fertilizer at the start of the active growing season in spring.
Pruning and Propagation Techniques
Regular removal of spent flower stalks, known as deadheading, maintains the plant’s tidy appearance and encourages new blooms throughout its long season. When a flower stem is completely finished, cut it back close to the basal foliage rosette to redirect energy toward new growth.
To rejuvenate an older, leggy plant or manage its size, aggressive pruning can be performed during winter dormancy or in late winter before new growth begins. The plant can be cut back by a third to a half of its height, stimulating new branching and resulting in a denser, more compact form for the following season.
Propagation is straightforward and offers a simple method for replacing older plants or expanding a collection. New plants can be easily started from stem cuttings taken during the pruning process. A successful cutting should have several nodes, which are the points where leaves or branches emerge from the stem.
The cuttings should be allowed to air-dry for a few days until the cut end forms a protective callus, which prevents rot and blocks pathogens. Once callused, the stem can be inserted into well-draining, gritty propagation media, and roots will develop quickly, often in a matter of weeks, especially if a rooting hormone is applied.