Leeks, a hardy biennial vegetable typically grown as an annual, are valued for their mild onion flavor and long, white edible shafts. Growing them successfully requires careful preparation and specific planting methods to maximize the length of this desirable white portion. This guide provides practical steps for transplanting leek seedlings into the garden, ensuring a strong start and a substantial harvest.
Preparing the Seedlings and Soil
The transition from an indoor environment to the unpredictable outdoors requires a gradual process called “hardening off.” This involves slowly acclimating the seedlings to direct sun, fluctuating temperatures, and wind over 7 to 10 days before transplanting. Begin by placing the seedlings outdoors in a shady, sheltered spot for a few hours, progressively increasing their exposure to sunlight and wind each day. This conditions the plant tissues, reducing the risk of leaf scorch and transplant shock.
Before planting, leek seedlings benefit from trimming both the foliage and the roots. Use sharp scissors to trim the leaves back to about 6 inches, which reduces moisture loss through transpiration after moving. Similarly, trim the roots to about one inch. This makes planting easier and encourages the development of new, fibrous feeder roots in the garden soil.
Leeks thrive in deep, fertile, well-draining soil, ideally with a neutral pH between 6.5 and 7.5. Since the goal is to produce a long, straight shaft, the soil must be loose and free of large stones that could impede growth. Prepare the planting area by deeply tilling the soil and incorporating organic matter, such as well-rotted compost or manure, to ensure fertility and adequate drainage.
Step-by-Step Planting Methods
Transplanting is best done in late spring or early summer, once the seedlings are approximately the thickness of a pencil and all danger of frost has passed. Leeks are set deep to maximize the desirable white portion of the stalk through blanching. This is achieved using one of two primary methods: the dibble method or the trench method.
The dibble method uses a long, pointed tool to create deep, narrow holes in the prepared soil. These holes should be approximately 5 to 6 inches deep to maximize the length of the blanched stem. A single trimmed seedling is dropped into the bottom of each hole, ensuring the roots point downward. The hole is not filled with soil.
Immediately after planting, water is used to settle the soil around the roots without completely filling the hole. The remaining open space will be filled by soil and rain as the plant grows. Space the individual seedlings 6 inches apart within the row, and allow 12 to 18 inches between the rows to ensure adequate air circulation and room for maintenance.
The trench method involves digging a shallow trench, typically 6 to 8 inches deep. Seedlings are placed along the bottom of this trench, positioned at the recommended 6-inch spacing. The sides of the trench are left open initially, and only enough soil is gently added to secure the roots and support the plant. This method prepares the bed for the ongoing process of hilling as the leeks grow.
Essential Care After Transplanting
The initial, deep watering is important for both methods. When using the dibble method, water hydrates the roots and washes fine soil into the hole to eliminate air pockets. For all seedlings, thorough watering immediately after transplanting helps them recover and establish quickly.
Throughout the growing season, leeks require consistent moisture due to their shallow root systems, so the soil should never be allowed to completely dry out. Regular, deep watering is more effective than frequent shallow watering, as it encourages roots to grow deeper. Leeks also benefit from light fertilization, especially with nitrogen, which can be applied as a side-dressing in the early summer to promote robust growth and thicker stalks.
To develop the long, white, tender shaft that is characteristic of a quality leek, the stems must be protected from light, a process known as blanching. This is accomplished by repeatedly mounding or “hilling” soil around the base of the growing plants as they mature. Begin this process when the leeks are about a half-inch thick, pulling soil up around the stems to cover the white portion.
Repeat hilling every few weeks, gradually increasing the depth of the soil around the stems. Take care not to get soil between the leaves, which makes the harvested leek difficult to clean. Excluding sunlight prevents chlorophyll formation, resulting in a milder, more tender blanched shaft. The trench method facilitates this hilling, as the sides of the trench are pulled back in stages to fill the depression.