Leeks are members of the onion family (Allium ampeloprasum var. porrum) typically cultivated as an annual crop. They are prized for their mild, sweet flavor and long, edible white stem, which is an aggregation of leaf sheaths. Growing leeks demands patience because they require a long period of growth to reach a desirable size. The entire process, from sowing the seed to the final harvest, spans several months, influenced by the planting method and the variety chosen.
Starting Leeks Seed or Transplant
The decision to start leeks from seed or purchase transplants directly impacts the overall time to harvest. Starting seeds indoors is the most common approach, requiring a substantial time investment before the plant enters the garden. Seeds are typically sown eight to twelve weeks before the last expected frost date.
Seedlings are nurtured indoors until they are about eight inches tall and the thickness of a pencil. This indoor period, lasting roughly two to three months, gives leeks a necessary head start in regions with shorter growing seasons. Purchasing pre-grown nursery transplants bypasses this initial two-to-three-month wait entirely, shortening the time until harvest.
Time to Maturity The Growth Cycle
The leek’s growth cycle is characterized by its long-season requirement, which varies significantly by cultivar. Once transplanted, leeks generally need 90 to 180 days to reach a size suitable for a full harvest. This means the total time from seed to harvest can range from five to eight months.
Varieties are broadly categorized into summer and winter types, which have distinct maturity schedules. Summer leeks, such as ‘King Richard,’ mature quicker, requiring only 90 to 100 days from transplanting. These varieties are generally smaller, have a milder flavor profile, and should be harvested before the first hard frost.
Winter leeks, like ‘Giant Musselburgh,’ are robust and cold-hardy, demanding 120 to 180 days after transplanting. This extended time allows them to develop a thicker stem and a more concentrated flavor. Winter varieties tolerate freezing temperatures for a prolonged period, but the total time, including the indoor start, can extend up to nine months.
Techniques for Maximizing Stem Length
A long, tender, white stem is achieved through a process called blanching. The white portion of the leek is simply the part of the stem shielded from sunlight, which prevents the development of chlorophyll. This lack of light exposure ensures the stem remains tender and non-fibrous.
The most common technique for blanching is hilling, which involves gradually mounding soil up around the stem as the plant grows. This process must be repeated several times throughout the main growth cycle. Alternatively, gardeners can plant seedlings into a deep trench and slowly fill the trench with soil as the leek matures, achieving the same effect.
Other methods involve slipping cardboard or plastic collars around the stem to physically block the light. This technique must be consistently applied over many weeks to encourage the development of a blanched shaft, typically three to six inches in length.
Knowing When to Harvest
Determining the precise moment to harvest leeks relies on visual cues rather than strictly following a calendar date. While a variety may be listed as a 120-day leek, readiness is best judged by the stem’s diameter. Most varieties are considered fully developed when the stem base reaches at least one inch in diameter, though some smaller cultivars mature at about a half-inch thick.
Full maturity often coincides with late summer or fall, but leeks offer a flexible harvest window due to their frost tolerance. Winter-hardy varieties can be left in the garden and harvested as needed, enduring temperatures as low as 20°F. Leeks covered with a protective layer of mulch can often be dug up fresh throughout the winter months.
The entire plant is harvested when ready, but it is important to pull them before they attempt to flower in the following spring, as this process causes the stem to become tough. Before pulling, use a garden fork to gently loosen the soil around the root system to avoid damaging the stem.