Foxglove (Digitalis species) is a valued garden plant, known for its height and characteristic bell-shaped blossoms that grow along a tall spike. Gardeners start these plants indoors to gain a significant jump on the growing season. This technique is particularly beneficial for biennial varieties, as early indoor sowing can often coax them into flowering in their first year. Starting seeds inside provides a controlled environment, which increases germination success rates compared to direct outdoor sowing.
Calculating the Optimal Indoor Starting Date
Determining the precise moment to sow foxglove seeds indoors depends on your local average last spring frost date. The standard recommendation is to sow the seeds between 8 and 12 weeks before this final expected frost. This calculation provides the necessary window for the seedlings to develop into robust plants before they are ready for the garden.
For varieties intended to bloom in the first year, aiming for 10 to 12 weeks is preferred. Since the seeds require 14 to 21 days to germinate, the initial growth phase is slow. Starting early ensures the seedlings have sufficient time to mature before the outdoor planting window, which occurs after all frost danger has passed.
Knowing your specific USDA Hardiness Zone or historical frost data is required for accurate timing. Planting too early results in leggy, overgrown seedlings that are difficult to manage indoors. Planting too late means the plants may not reach a size capable of flowering in their first year.
The traditional foxglove is a biennial, establishing a leaf rosette in the first year and flowering in the second. Modern breeding has produced annual-flowering cultivars that benefit most from an early indoor start to force blooms within a single season. Starting seeds indoors provides the necessary head start to establish a vigorous root system before summer heat arrives.
Essential Steps for Indoor Sowing
Sowing foxglove seeds requires careful attention due to their minute size. Begin by filling clean seed-starting trays or small pots with a sterile, fine-textured seed-starting mix. This mix is formulated to be light and disease-free. Avoid using heavy garden soil, which can compact easily and harbor pathogens that harm delicate seedlings.
Foxglove seeds require light to initiate germination, meaning they must be surface-sown and not covered with soil. Scatter the tiny seeds thinly across the moistened surface and gently press them down for good contact. A thin dusting of fine vermiculite can be applied to anchor them slightly, which allows light penetration while maintaining surface moisture.
Maintain the germination environment at a consistent temperature, ideally between 60°F and 70°F, often achieved using a heated seedling mat. Consistent moisture is crucial during the two-to-three-week germination period; the medium should be kept evenly damp but never waterlogged.
Water from the bottom by placing the trays in a shallow pan until moisture wicks up through the soil, preventing seed dislodgement. Immediately after emergence, place seedlings under bright grow lights for 14 to 16 hours daily. A sunny windowsill is rarely sufficient to provide the intense light needed to prevent the young plants from stretching and becoming weak.
Hardening Off and Transplanting Seedlings
Before young foxglove plants are moved into the garden permanently, they must undergo hardening off, a gradual process of acclimatization. This transition prepares them for the harsh realities of direct sun, wind, and fluctuating outdoor temperatures. The hardening off process should span approximately 7 to 14 days to minimize the risk of transplant shock.
Start by placing the seedlings outdoors in a sheltered location, such as a porch or beneath a dense tree canopy, for a short period—perhaps just one or two hours on the first day. This initial exposure should be protected from strong winds and direct sunlight. Over the following days, gradually increase the amount of time the seedlings spend outside and slowly expose them to brighter light and more open air.
Final transplanting into the garden should only occur after all danger of the last spring frost has passed. Prepare the planting site by amending the soil with organic matter and ensuring good drainage, as foxgloves prefer rich, moist soil. Dig a hole slightly larger than the seedling’s root ball and gently loosen any densely packed roots before placing the plant in the ground.
Set the seedling into the soil at the same depth it was growing in its pot, taking care not to bury the crown or any lower leaves. Space the plants according to the variety’s mature size, typically 12 to 18 inches apart, to allow for adequate air circulation. Immediately after planting, water the seedlings thoroughly to settle the soil around the roots and help them begin their adjustment to their new home.