Lupine, with its striking spires of colorful flowers, is a beloved perennial. However, lupine seeds possess a natural survival mechanism that makes germination difficult without intervention. Successfully growing lupine from seed requires specific pre-treatments to overcome its dual-layered dormancy. These preparations mimic the natural processes the seed undergoes in the wild, ensuring a high rate of germination success.
Understanding Seed Dormancy in Lupine
Lupine seeds exhibit dormancy, a sophisticated defense strategy that prevents sprouting during unfavorable conditions. This mechanism is often a combination of two types: physical and physiological. Physical dormancy is caused by the seed’s extremely hard, impermeable outer shell, or testa. This tough coat prevents water absorption, which is the first step required for the embryo to begin growth.
Physiological dormancy involves internal chemical inhibitors that must be neutralized before the seed can sprout. These inhibitors break down only after the seed experiences a prolonged period of cold, moist conditions. This ensures the seed germinates in spring, giving the new seedling the best chance of survival. Overcoming both the physical barrier and the physiological inhibitors dictates the two primary steps in successful lupine seed preparation.
Detailed Steps for Cold Stratification
Cold stratification overcomes physiological dormancy by artificially replicating a winter season. This technique involves exposing the seeds to low temperatures while keeping them consistently moist for several weeks. To perform this, mix the seeds with a sterile, inert medium, such as fine sand, vermiculite, or a damp paper towel. Placing this moistened mixture in a sealed container or plastic bag is the most reliable method.
The container should be placed in a refrigerator, maintaining a stable temperature between 34°F and 40°F (1°C and 4°C). This cold, moist period typically lasts four to eight weeks, depending on the lupine variety. The combination of cold and moisture slowly breaks down the chemical inhibitors, preparing the seed for rapid growth once exposed to warmer spring temperatures.
Scarification: A Necessary Pre-Treatment
Scarification addresses physical dormancy and must occur before, or concurrent with, cold stratification. This process weakens the hard outer seed coat, allowing moisture to penetrate the embryo. Without scarification, water cannot reach the seed’s interior, and the seed will not germinate, regardless of stratification length.
The most common method is mechanical scarification, which involves lightly abrading the seed coat. This is accomplished by gently rubbing the seeds between two pieces of fine-grit sandpaper or carefully nicking the seed with a small file or knife. The goal is only to compromise the outer layer, not to damage the inner embryo. Alternatively, seeds can be dropped into water that has just boiled, removed from the heat, and allowed to soak for 12 to 24 hours. Combining scarification with cold stratification provides the highest germination rates.
Successful Sowing and Germination
Once the seeds have been scarified and stratified, they are ready for planting in a prepared seed-starting mix. Because lupines develop a deep taproot that dislikes disturbance, sow them directly into the garden or in deep seed-starting containers. Plant the seeds shallowly, covering them with approximately one-eighth to one-quarter inch of soil.
The ideal soil for germination is well-draining, slightly sandy, and maintains a mildly acidic to neutral pH. After sowing, keep the soil consistently moist and place the containers in an environment where the temperature is between 65°F and 75°F (18°C and 24°C). Germination typically occurs within two to three weeks under these optimal conditions. If starting indoors, ensure the seedlings are hardened off—gradually acclimated to outdoor conditions—before transplanting them.