Delphiniums, also known as Larkspur, are popular garden flowers celebrated for their majestic, towering spires of blue, purple, pink, or white blooms. These plants bring vertical drama and old-world charm to garden beds. While mature plants are readily available, growing these spectacular flowers from seed is a rewarding process that requires careful attention. This guide will walk through the necessary preparation and planting techniques for achieving a thriving stand of delphiniums.
Preparing Seeds and Selecting the Sowing Time
Delphinium seeds benefit significantly from a cold stratification period, a process that mimics the natural winter conditions needed to break dormancy. This chilling treatment is necessary because the seeds contain germination inhibitors designed to prevent sprouting until conditions are favorable. A simple method involves placing the seeds in a damp paper towel inside a sealed container and refrigerating them for two to three weeks.
The ideal time for sowing these prepared seeds is indoors, about eight to ten weeks before the last expected frost date. Sowing indoors provides a controlled environment for delicate seedlings and allows the plants to mature enough to produce flowers in their first growing season. This early start maximizes the chance of achieving impressive flower spikes by summer.
Direct sowing outdoors in late fall is a less reliable alternative, as unpredictable weather and pests often result in lower germination rates. By stratifying the seeds manually and starting them indoors, gardeners gain greater control over the initial, fragile stages of the plant’s life cycle.
Step-by-Step Indoor Sowing Method
Begin by selecting appropriate materials to ensure a sterile and supportive environment for the tiny sprouts. Use clean trays or small pots filled with a sterile, fine-textured seed-starting mix. This mix provides a light, aerated structure that prevents compaction and promotes healthy root development. Before sowing, thoroughly moisten the mix until it is uniformly damp but not saturated, allowing excess water to drain completely.
Carefully place the stratified seeds on the surface of the soil. Delphinium seeds require light for optimal germination, so they should not be buried deeply. A light dusting of fine vermiculite or a thin layer of the seed mix can be used to cover the seeds, providing contact with the medium while allowing light penetration. This light covering also helps maintain moisture around the seed coat.
Ideal germination temperatures range between 60°F and 68°F. Some growers find that covering the trays with an opaque material for the first few days can improve germination rates. Always label your trays immediately with the variety and the sowing date for tracking progress and planning the rest of the growing season.
Managing Germination and Acclimation
Once the first sprouts emerge, move the trays immediately to a location that provides ample light. This prevents the seedlings from becoming stretched and weak. Placing them under specialized grow lights, positioned a few inches above the seedlings, provides the intense, consistent light required. Simultaneously, reduce the temperature to a cooler range, ideally between 55°F and 65°F, which encourages stocky, robust growth.
Moisture control is important, as both too much and too little water are detrimental. If humidity domes were used, remove them promptly after sprouting to increase air circulation and prevent fungal issues like damping off disease. Water from the bottom to allow the soil to wick up moisture, keeping the surface drier and discouraging fungal growth.
As the seedlings develop their first set of true leaves, thin them out to ensure the strongest plants have sufficient space. If started in communal trays, carefully pot the seedlings into individual, slightly larger containers once they have two sets of true leaves, using a slightly richer potting mix. This gives the developing root systems room to expand before moving outdoors.
The final step before planting is hardening off, which acclimates the young plants to the outdoor environment. Over seven to ten days, move the delphiniums outside for increasingly longer periods each day, starting in a sheltered, shady spot. This slow introduction to sun, wind, and temperature fluctuations ensures the plants survive their permanent placement in the garden bed.