Overwintered leeks, photo by Twin Oaks Community
Unlike onions, leeks grow independently of day-length and will stand in your garden at temperatures colder than many other vegetables can handle, getting bigger until you harvest them. A flexible harvest date during fall and winter is a boon to gardeners seeking a steady supply of vegetables. Planting dates can be chosen to suit your climate. Both the white and the green parts of the leek are delicious. Only the tougher parts of the outer leaves need to be composted. Late spring or early summer is the time to transplant leek seedlings started earlier in spring. That is the aspect of growing leeks that I'll cover in this post.
Photo by Small Farm Central
Leeks come in two main types: the less hardy, faster-growing lighter green varieties, which are not winter-hardy north of Zone 8. We like Lincoln, and King Richard (both 75 days). They are hardy down to 12°F (-11°C). American Flag aka Giant Musselburgh (105 days) is good for overwintering in climates milder than our 7a. It and Jaune du Poiteau, are hardy to 10°F (-12°C).
The blue-green hardier winter leeks such as Bulgarian Giant, Laura, Tadorna (100 days) are hardy to 5°F (-15°C). For winter leeks we also like King Sieg (84 days) and Bleu de Solaize (105 days) and Bandit (120 days). A few leeks (Alaska, Durabel) are hardy down to 0°F (-18°C).
Crop Requirements for Leeks
Leeks do best in well-draining soil rich in nutrients, with a pH of 6.5, and good sunlight. Ideal growing temperatures are 55°F–75°F (13°C–24°C). Growth is slow above 77°F (25°C), but the plants do not deteriorate and will resume growth when cooler weather arrives.
Growing Leeks from Seed
If you have a long enough growing season and don’t want leeks in summer, you can delay sowing till March as we do. We transplant in late May or early June, in beds cleared of early spring crops. People with a longer growing season (zones 8–9a) can plant two crops: the first 12–14 weeks before the last spring frost, and the second in mid-July, to transplant in late September or early October. In zones 9b–11, sow only in July, and use a bolt-resistant variety for leeks to harvest in the new year.
Step-by-Step Leek Planting Instructions
The ideal leek size for transplanting is between a pencil lead and a pencil in thickness. We plant at 6" (15 cm) spacing, four rows to a 48" (1.2 m) bed. People wanting really huge leeks use wider spacings. We use a special planting technique, in order to develop long white shanks, which are prized more than the equally edible green parts. If you have a crew, divide up and specialize. If not, take it one step at a time.
1. If the soil is dry, water it well, preferably the day before.
2. Make parallel V-shaped furrows, 3" (8 cm) deep, along the bed.
3. Set out a fiberglass tape measure along one row.
4. Make holes 6" (15 cm) apart in the furrows. Use the tape measure for one row and then eyeball the other rows to offset the leeks in alternate rows. The best tools for this job are homemade “dibbles” or dibblers made from broken shovel or digging fork handles, with the end sharpened to a point. The tool needs to have a diameter of 1.5–2" (4–5 cm). The depth of the holes is determined by the height of the transplants, and probably needs to be 3" (8 cm) or so.
5. If the holes cave in, stop and water the soil more before proceeding.
6. Transfer some leek seedlings from open flats or a nursery seedbed to a small bucket containing an inch or so of water. We make buckets from one-gallon (four-liter) plastic jugs with the top cut off. A rope handle knotted into holes at the top of the new bucket makes it easy to carry.
7. Resist any temptation to trim either the roots or the tops of the leeks.
8. To transplant, take a leek plant, shake it free from its neighbors and decide whether to plant it. Discard the ones thinner than pencil leads. If the plant is a good size and looks healthy, twirl it as you lower it into the hole to prevent the roots folding back on the plant and pointing at the sky — they need to grow downwards. This works best if the roots are still wet and muddy from the water bucket. Bobbing the plant up and down as you settle it in the hole will help a transplant that has slightly bunched roots.
9. If at first you don’t succeed, remove the plant from the hole, dip it back in the water and try again. Soon you will develop this quirky planting skill, and will be able to move along the row at a good pace. Ideally just the tips of the leaves will poke out of the holes, not more. Get the depth of the hole-making adjusted to suit the prevailing plant height. The furrow-and-hole combination creates the depth for growing a long white shank.
10. Surprising as it may sound, it is not necessary or desirable to fill the holes with soil (you don’t want to bury the seedlings). The soil fills in naturally as the plants grow tall enough to survive the depth.
11. Next gently fill each hole with water, either from a low-pressure hose or watering can. The goal is to water the plant roots, adding little or no soil to each hole. The shelter of the hole helps the plant get over the transplant shock, and because leeks have slender tough leaves, they do not lose a lot of water by transpiration. This means that transplanting is possible in quite hot weather.
12. Keep the soil damp for several days after planting,
13. Then give one inch (2.5 cm) of water per week as needed.
14. Like other alliums, leeks do not compete well with weeds, so hoe as needed, at least once a month. Hoeing will help fill the holes.
Some people hill up their leeks, but with this method it is not necessary. Our method avoids the problem of soil getting above the point where the leaves fan out from the stem, which makes them very hard to clean later.
Pam Dawling works in the vegetable gardens at Twin Oaks Community in central Virginia. She often presents workshops at MEN Fairs. Pam also writes for Growing for Market magazine. Her book, Sustainable Market Farming: Intensive Vegetable Production on a Few Acres, is available at www.sustainablemarketfarming.com, Pam's blog is on her website and also on facebook.com/SustainableMarketFarming.
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