Growing lavender from seed begins with understanding the specific conditions required to awaken the embryo inside its protective shell. Germination is the biological mechanism where a dormant seed sprouts into a new plant. Successfully propagating Lavandula varieties requires replicating the precise environmental cues that signal the end of winter and the start of the growing season. This involves breaking seed dormancy, a state that prevents germination even when conditions appear favorable.
Light Requirements for Germination
Lavender seeds are photoblastic, meaning their germination is promoted by light exposure. For most common types of lavender, light is required to trigger the sprouting process. This necessity is linked to the small size of the seed, which contains limited energy reserves to push a sprout through deep soil.
Therefore, lavender seeds should be surface-sown or pressed lightly into the seed-starting mix without being buried. If covering the seeds, use only a very thin layer of fine vermiculite or grit, no more than 1/8 inch deep. This shallow planting depth ensures the seed receives the light necessary for germination. Adequate light exposure, often provided by a grow light for 12 to 16 hours a day indoors, is necessary once the seeds are moved to their warm environment.
Essential Pre-Treatment: Cold Stratification
Even with perfect light and moisture, many lavender seeds, particularly those from Lavandula angustifolia, will not sprout without an initial period of cold treatment. This is due to seed dormancy that must be broken by cold stratification, which mimics the seed resting in cold, moist soil throughout winter.
This pre-treatment involves exposing the seeds to temperatures near freezing for an extended period. A common method is to mix the seeds with a sterile, moist substrate, such as damp paper towels, fine sand, or peat moss. The mixture is then placed inside a sealed plastic bag or container.
The seeds require refrigeration between 35°F and 40°F. This moist chilling period should last a minimum of three weeks, though four to six weeks is recommended for maximum success. This duration allows the seed coat to soften and internal chemical inhibitors to break down, preparing the embryo for growth. Skipping this step often results in erratic or low germination, regardless of subsequent light or temperature.
Achieving the Ideal Germination Environment
Once cold stratification is complete, the seeds are moved to a warm, brightly lit environment to begin germination. The ideal temperature range for sprouting is between 65°F and 75°F. Using a seedling heat mat beneath the planting tray helps maintain this consistent warmth, which is difficult to achieve with ambient room air temperature alone.
Equally important is maintaining consistent moisture in the seed-starting medium without waterlogging. A sterile, well-draining mix designed for starting seeds is superior to heavy garden soil, which can compact and harbor pathogens that cause damping-off disease.
Maintaining high humidity prevents the shallowly planted seeds from drying out. Placing a clear plastic dome or plastic wrap over the seed tray creates a miniature greenhouse effect to trap moisture. As soon as the first sprouts appear, the dome should be removed to allow for air circulation and prevent fungal growth, a common threat to young seedlings.