Stonecrop, belonging to the genus Sedum, is a popular group of ornamental plants known for their toughness and ability to thrive where many others fail. Often grown for their attractive foliage and late-season blooms, their resilience frequently leads to questions about their true nature. The common name “stonecrop” hints at their preference for rocky, poor soil, but it does not fully explain their botanical classification.
The Succulent Classification
Stonecrop is a succulent, confirmed by its membership in the plant family Crassulaceae, which is dominated by water-storing species. Succulents are defined by their thick, fleshy tissues, which retain moisture during dry periods. Sedum species exhibit this trait primarily in their leaves and sometimes their stems, which are noticeably swollen and dense.
Water retention is facilitated by several specialized features. The leaves often have a thick, waxy outer layer called a cuticle, which minimizes water loss through surface evaporation. Many stonecrop species also employ Crassulacean Acid Metabolism (CAM). This process allows the plant to open its stomata only at night when temperatures are cooler, reducing the amount of water vapor that escapes during the heat of the day.
Diversity Within the Sedum Genus
The genus Sedum encompasses hundreds of species that vary widely in size, color, and growth habit. Species are generally grouped into two main categories based on their form: low-growing and upright. This diversity impacts how they are typically used in landscaping.
Low-growing or creeping stonecrops are mat-forming, spreading along the ground and often reaching only a few inches in height. These varieties are frequently used as groundcover, in rock gardens, or spilling over containers. Upright or clumping stonecrops form taller, defined mounds of foliage, growing one to three feet tall. These taller forms are popular for use in borders and perennial beds, providing late-season interest. Many popular upright stonecrops, such as ‘Autumn Joy,’ have been botanically reclassified into the genus Hylotelephium, though they are still widely referred to as Sedum in horticulture.
Growing Requirements for Stonecrop
Successful cultivation relies on providing conditions that mimic their native, often dry and rocky, habitats. Most Sedum varieties thrive in full sun, requiring at least six hours of direct sunlight daily. Insufficient light leads to weak, “leggy” growth and reduced flowering, often causing upright types to flop over.
Soil composition is another element of stonecrop health, and the focus must be on drainage. The plant requires a well-draining, gritty, or sandy soil mix, as it is susceptible to root rot in heavy clay. They perform best in lean or average soil and generally do not require supplemental fertilizer, since overly rich soil can promote weak growth.
Watering should be deep but infrequent, as the succulent leaves store moisture. Once established, stonecrop only requires supplemental water during extended periods of heat or drought. A rule of thumb is to allow the top two inches of soil to dry out completely between waterings.