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Onions & Leek Project List

Onions are simply a must have, and leeks are the perfect seasonal companion in your garden and in your cooking. Both are easy to grow if you follow basic steps.

  • Compost — Loose, compost rich soil is required by these crops. Add more seasonally.
  • Garden Soil Builder — Soil Mender’s blend of aged humus, manure, and alfalfa meal is excellent to amend soils intended for vegetables.
  • Organic Fertilizer — Try Espoma’s Plant-tone or Hasta-Gro for their higher nitrogen content.
  • Liquid Seaweed — An organic extract that strengthens plants for better resistance to temperature fluctuations, stress, and disease.
  • Mulch — Only minimal mulching is required for these crops. Protect soil with at light layer of mulch, such as pine straw.

TIMING: For your greatest chance of success, rather than by seeds, young onions (called slips) as well as leeks should be planted in January. These are generally more disease resistant than planting by seed or transplants.

SELECTION: Onions are classified according to how much daylight they need in order to bulb. Short day, 10 to 11 hours; intermediate, 12 to 13 hours; and long day 14 to 16 hours. Short day varieties produce large bulbs anywhere in the state, and are milder. NHG offers short to intermediates. Leeks are not daylight sensitive.

SITE: Start with a raised bed or in-ground garden space that gets full sun and has rich, very loose soil that is full of organic matter and has been maintained organically (preferably). Onions appreciate an only slightly acid soil.

PREP: Onions are sold in bunches as ‘sets’. Individual slips may be slightly different in size; select the largest for full-size onions, and the smaller for green onions, if desired, though all will mature to full size given time. Plants may appear dry, but do not worry; if they cannot be planted immediately, remove them from the bag and spread them out in a cool, dry area. It is okay if the roots and tops begin to dry slightly. Do not water them or place them in water; keep them dry in an airy, cool location until they can get in the ground.

PLANTING OPTIONS:

  • Dig a trench 4” deep, place the fertilizer in the trench, and then add 3” of soil on top of the fertilizer. Onions must have fertilizer available as soon as they are planted.
  • Plant the onions approximately 1” deep with 4” spacing. No more than 1” deep: you will have some of the white showing. The plants will do much better if they are growing at or near the surface.
  • For green onions, plant the slips as close as 2” apart and harvest every other one early, prior to bulbing. This will leave room for the remaining ones to get full size.
  • Do not place any additional soil on top, as this will not allow the bulb to form.

PLANTING LEEKS: The leek is a member of the onion family, but is milder than either onions or garlic. Leeks do not form bulbs or produce cloves, but develop an edible 6-10” stem up to 2” in diameter. Space plants 4-6” apart in rows 6-12” apart. To keep them white and tender, plant deeply about 6-8”, so that only a few inches remain. Water slowly right after planting. Through the growing process, mound soil around the leeks to block sunlight, lest it turn green and tough.

CULTURE:

  • Water slowly and thoroughly after planting. Regular watering is highly important to successful onions and leeks. Keep the soil just moist; never wet. Watering needs increase the closer it comes time to harvest; if leaves turn yellow, reduce frequency. Near harvest time, withhold water so that skins will ripen for better storing. Keep the soil around the onions weed-free, as onions do not tolerate crowding. Keep cultivation shallow. These plants have few pest or disease problems. Protect onions from extremely cold weather. Both onions and leeks can be stored in the ground until needed.

FEED: About 3-4 weeks after planting, watch for 5-6 leaves to have grown, and begin fertilizing. The size of the bulb depends upon the number and size of green leaves or tops at the time of maturity. For each leaf there will be a ring of onion; the larger the leaf, the larger the ring will be. Leeks are fed the same way as onions.

  • Repeat fertilization every 2-3 weeks for both onions and leeks. Sweeter onions are produced with better soil fertility, even moisture, and less soil acidity (sulfur). Bulbing has begun when the soil near the bulb begins to crack and the neck is slightly softer. Stop fertilizing when you see bulbing begin. Pull mulch away from onions as it becomes visible, so that it remains dry and continues to develop.

HARVEST ONIONS: For green onions, plants the size of a pencil can be harvested early. When stalks turn yellow and begin to fall over (generally in May) it’s time to harvest full-size onions. Harvest the bulbs, leaving the green tops. Pull, or gently dig up the onion and lightly brush off excess soil. Remove any with bruises or soft spots. Do NOT wash them, as they must be cured first in order to store properly.

CURE: Before you store your onions, you must cure them, or they will rot. Drying is faster outdoors: Lay them spaced apart in shade, for at least 3 days to dry. Indoors, lay onions in a single layer in a cool, dry place out of direct sunlight (a pantry or garage works well) and it will take about a week. Good air circulation is key to prevent rotting. The bulb will feel dry and the outer layer will become papery, and the skin one color. The top growth down to the neck will be completely dry when they are fully cured.

  • Once dry, clip off any longer roots, and cut the stalk off to about 1” from the bulb. Store them in an onion net or basket in a cool dry place. If you use a net, tie a knot in between each onion so they don’t rest on each other, and you can clip the bottom onion off when you’re ready to use it. Use sweeter varieties first, as more pungent ones do not store as well. Check often, and remove any that begin to soften prematurely, as it will affect the quality of the remaining onions.

HARVEST LEEKS: Approximately around the same time as you are harvesting onions, use a garden fork to carefully harvest when the shaft is about 1”-2” in diameter. Gently shake them, then rinse well. Since they are best used fresh, store in a damp paper towel in a bag with air holes in a refrigerator for up to 7-10 days. Or, blanch and freeze. Leeks do not store well, but smaller leeks will store better than larger ones. Just before using, trim leaves and slice the leek in half lengthwise, and rinse again.

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