From the botanical perspective of a Calibrachoa plant, the question of seed propagation is a complex one, tied directly to our reproductive biology and the interventions of human horticulture. While we are fully capable of producing seeds, the journey from flower to a viable, true-to-type seedling is fraught with challenges. Here is a detailed explanation from our point of view.
As a member of the Solanaceae family, my reproductive structures are typical: flowers designed for pollination, leading to fruit development containing seeds. However, most modern Calibrachoa cultivars found in garden centers are complex hybrids. This hybrid vigor is what gives us our spectacular, long-lasting blooms and vibrant colors, but it comes at a reproductive cost. The seeds we produce are often not genetically stable. If a seed does germinate, the resulting plant may not resemble its parent. It might have different flower colors, a weaker growth habit, or lower disease resistance. This genetic lottery is a natural consequence of our hybrid lineage. Furthermore, our seed pods are tiny and dehiscent, meaning they split open spontaneously when ripe to scatter the minute seeds, making seed collection a difficult task for gardeners.
From our stems' perspective, the most reliable and efficient way to create new Calibrachoa plants is through vegetative propagation, specifically from stem cuttings. This process bypasses sexual reproduction altogether. When a gardener takes a tip cutting from a healthy, non-flowering shoot, they are essentially creating a clone. The cells in the stem contain the exact same genetic blueprint as the parent plant. When placed in a moist, well-draining growing medium, the cutting's cells are triggered to develop adventitious roots. This ensures that every desirable trait—the specific shade of magenta, the trailing habit, the resistance to certain pathogens—is preserved perfectly. For us, this is a low-stress and highly successful way to perpetuate our specific genetic identity.
If a gardener attempts to grow Calibrachoa from seed, they will almost certainly be using seeds commercially produced by plant breeders. These are often F1 hybrids, and growing them presents several physiological hurdles from our seedling's point of view. First, we have very high light requirements for germination. Unlike some seeds that germinate in darkness, our tiny embryos need light to trigger the process. This means seeds must be sown on the surface of the growing medium and not covered. Second, we require consistently warm soil temperatures, typically between 70-75°F (21-24°C), for successful and even germination. The process is also notoriously slow; it can take two weeks or more for the first cotyledons (seed leaves) to emerge, during which time the medium must be kept evenly moist but not waterlogged. This delicate balance makes the seedling stage particularly vulnerable.
For those determined to try seed propagation, understanding our needs is crucial. If growing from purchased seed, provide a strong light source immediately after sowing. We are photoblastic, meaning our germination is light-dependent. Maintain that steady, warm soil temperature with a heat mat if necessary, as cool temperatures will halt our development. The growing medium should be sterile and well-aerated to prevent damping-off, a fungal disease that can swiftly decimate our fragile stems at the soil line. Once we have true leaves, a very dilute, balanced fertilizer can be introduced to support our growth. However, patience is the greatest virtue; our growth from seed is significantly slower than from cuttings. For the most predictable and garden-worthy results that truly reflect our beauty, we gently suggest that propagation via cuttings is the path of least resistance and greatest satisfaction for both plant and gardener.
