Sweet Alyssum (Lobularia maritima) is a low-growing annual frequently used as groundcover or edging. Although cultivated as a seasonal annual, it is a prolific self-seeder. The successful appearance of new “volunteer” plants depends heavily on specific environmental conditions and garden practices.
The Self-Seeding Mechanism
The process of self-seeding begins in late summer and early fall as the plant’s tiny flowers fade. Spent flowers transition into small, inconspicuous seed pods, characteristic of the Brassicaceae family. These capsules mature and dry out, eventually splitting open to release minuscule, dust-like seeds directly onto the soil surface beneath the parent plant.
Alyssum seeds rely on passive dispersal, relying on gravity rather than external carriers like wind or animals. This mechanism ensures a high concentration of seeds remains in the immediate location for spring germination. The timing of the seed drop is essential for the seeds to be exposed to winter chilling, which helps prepare them for sprouting.
Environmental Factors for Successful Germination
For the dropped seeds to sprout into new plants, several environmental variables must align during the winter and early spring months. Alyssum seeds are light-dependent germinators, meaning they must remain on or very close to the soil surface; burying them even slightly prevents sprouting. Successful overwintering depends on the severity of the cold, as prolonged, deep-freezing temperatures below 28°F can compromise seed viability.
The seeds need a sustained period of consistent moisture, which typically occurs during the early spring thaw, to break dormancy and begin the growth process. Well-draining soil is required, as soggy or waterlogged conditions can cause the seeds to rot before they establish roots. Excessive soil disturbance, such as tilling or aggressive weeding, can move the seeds too deep or expose them to rapid desiccation, reducing the chance of a successful volunteer crop.
Promoting Volunteer Plants Next Season
Gardeners can increase the likelihood of volunteer plants by making intentional changes to their maintenance routine during the latter half of the growing season. The primary action is to stop deadheading, or removing spent blooms, from late summer onward. Allowing the flowers to remain permits the necessary energy investment into the formation and maturation of the seed capsules.
It is beneficial to avoid applying heavy layers of organic mulch over the areas where the alyssum grew, as this blocks the sunlight needed for germination. In the spring, gardeners should resist the urge to heavily till or work the topsoil near the old plants. Limiting soil disruption protects newly germinated seedlings and maintains the shallow depth required for survival. Gently shaking the dried stems in early spring helps ensure remaining seeds drop directly onto the soil surface.