Leeks, a biennial member of the Allium family alongside onions and garlic, are commonly cultivated as an annual vegetable for their edible stems. The plant’s life cycle culminates in the production of seeds. Understanding the appearance of these seeds is helpful for gardeners aiming to save their own stock or correctly identify store-bought seed packets.
The Physical Characteristics of Leek Seeds
Leek seeds are notably small, appearing as tiny, deep-colored specks, often compared to the size of a pinhead. Their color is a dense, non-reflective coal black or dark brown, which helps them absorb warmth for germination. The seeds are not perfectly round but possess an irregular, angular, or faceted shape, sometimes described as rhomboidal or teardrop-like. The texture is slightly rough, matte, and sometimes faintly wrinkled or pitted. While small, leek seeds are generally larger than onion seeds, with the average weight of 1,000 seeds falling into a range of 2.5 to 3.0 milligrams.
How Leek Seeds Form and Mature
Leeks are true biennials, completing their life cycle by producing flowers and seeds in their second year of growth. If left unharvested, the plant sends up a tall, rigid flower stalk (scape) the following spring, a process called “bolting” that redirects energy away from the edible stem. At the top of the stalk, a large, spherical flower head (umbel) develops, packed with miniature purple and white florets. Once pollinated, these mature into small seed capsules where the black seeds develop. Seed viability is maximized when the seeds are allowed to fully mature and dry on the stalk until the capsules turn from green to a papery white or brown.
Sowing and Germination Requirements
Leek seeds must be sown shallowly, typically at a depth of 1/4 to 1/2 inch, as planting too deep can prevent the delicate seedlings from pushing through the soil surface. For optimal sprouting, the soil temperature should be consistently between 60–75°F. Cooler soil temperatures can slow the process, but germination can occur in temperatures as low as 50°F. Under optimal conditions, seedlings typically emerge within 6 to 16 days. Consistent moisture must be maintained throughout the germination period without overwatering, and leek seeds maintain good viability for approximately two to three years when stored properly.