Sedum, commonly known as Stonecrop, is a perennial plant recognized for its thick, succulent foliage and remarkable drought tolerance. These plants offer diverse garden applications, ranging from low-growing groundcovers to taller, upright varieties that provide structure to borders. Cultivating Sedum from seed allows gardeners to start a large number of plants, often resulting in specimens that adapt well to local conditions. This process requires attention to detail to ensure successful germination and the development of hardy seedlings. This guide details the specific steps for starting these popular plants from tiny seeds.
Essential Preparation and Timing
The process begins with timing the sowing for success, which typically means starting the seeds indoors six to eight weeks before the final expected frost date in spring. Preparing the growing medium is necessary, as Sedum requires a substrate that drains water rapidly to prevent root issues. A sterile, well-draining seed-starting mix works well, or a blend of standard potting soil, sand, and perlite can be used to mimic the lean, porous conditions Sedum prefers.
Choosing a shallow tray or pot provides adequate space for the fine root systems. For some specific varieties, cold stratification may be beneficial to break seed dormancy and increase germination rates. This involves placing the seeds in a moist, cold environment, such as a refrigerator, for approximately 14 to 30 days before sowing. This pre-treatment simulates the natural winter conditions the seeds would experience outdoors.
Sowing the Tiny Sedum Seeds
Sedum seeds are exceptionally small, which dictates a specific method for planting to ensure they receive the necessary light for germination. Instead of burying the seeds, they must be surface-sown, meaning they are sprinkled evenly across the prepared, moistened soil surface. Gently pressing the seeds into the soil with a flat object ensures good seed-to-soil contact without covering them.
Applying a thin layer of fine horticultural vermiculite over the seeds can help retain surface moisture while still allowing light penetration. This layer also helps suppress the growth of algae and minimizes issues with fungus gnats. To water the tray after sowing, use a misting bottle or employ bottom watering, where the tray sits in a shallow container of water, allowing the soil to wick moisture upwards. Covering the tray with a clear plastic dome or plastic wrap will maintain a high humidity level, which is beneficial for germination.
Care During Germination and Early Growth
The environmental conditions following sowing must be carefully controlled to prompt germination, which typically occurs within 14 to 21 days. Sedum seeds respond best to warm temperatures, ideally kept consistently between 65 and 72°F during this period. Since the seeds are photoblastic, meaning they require light to sprout, placing them under a dedicated grow light is often the most reliable method.
Grow lights should be positioned approximately three to four inches above the soil surface and kept on for about 16 hours a day. Once the seedlings emerge, the plastic cover or humidity dome should be gradually removed to improve air circulation and prevent fungal diseases like damping off. Maintaining consistent moisture is necessary, but the soil surface should be allowed to dry slightly between waterings. The seedlings will remain relatively small for the first six to eight weeks.
Hardening Off and Transplanting
Before moving the young Sedum plants to their permanent outdoor location, they must undergo a transition process called hardening off. This procedure strengthens the plant’s cell structure, preparing them for the rigors of direct sunlight, wind, and temperature fluctuations. Begin by placing the trays in a sheltered outdoor area for a short period, such as 30 minutes to an hour, gradually increasing the exposure time daily over the course of a week.
The seedlings are ready for their final planting site once the danger of frost has fully passed and they have developed several sets of true leaves. Sedum thrives in a location that receives full sun (at least six hours of direct light daily) and requires a well-drained soil composition. When transplanting, dig a hole large enough for the root ball and place the plant so the top of the roots sits level with the surrounding soil. Space taller, clumping varieties up to two feet apart, while low-growing, creeping types need six to twelve inches of space to spread effectively.