Days to germination: 8 to 20 days
Days to harvest: 100 to 135 days
Light requirements: Full sun or light shading
Water requirements: Regular watering
Soil: Rich, loose and well-drained
Container: Not particularly suitable
In many ways, leeks are a lot like very large green onions. They look similar but their flavor is milder.
These are a cool-weather vegetable, so you may want to grow either a spring crop or a fall crop (or both). There are some varieties of leeks that differ in their maturity times and sizes, but you don’t get the huge range of options as you would with some other plants.
Leeks are usually eaten for their taste not their nutritional content. There is manganese, vitamin C and iron in leeks but not in huge amounts. Raw leeks are very nice in summer salads, and they can also be cooked in a variety of ways. Leek and potato soup is one of the best-known ways to cook them.
Starting from Seed
To take advantage of the cool spring weather, you should put your plants out as seedlings rather than direct seeding into the garden. Your seeds should be just 1/2 inch under the soil, and planted indoors about 6 weeks before your last frost date.
Plant a few seeds each in 3″ pots, and thin them down to the strongest seedling once they have sprouted. Don’t start them in little trays because they will be fairly large by the time you have to transplant them.
For a later fall crop, you follow the same procedure starting your batch of seedlings indoors right around the last frost date. Once they are around 8″ high, they are ready to be planted out.
Your plants should be at least 6 inches high by transplant time, which is right around your last frost date. Young leeks are fine with a few light frosts.
Leeks are typically grown in rows, starting off in trenches that are filled in as the plant grows. Dig your soil to loosen it up, at least 6 inches deep and add a generous helping of compost or complete fertilizer mix.
Space your seedlings to about 6 inches apart in a furrow around 4 inches deep. If you are growing more then one row, keep them about 20 inches apart.
As your leeks grow, slowly fill in the trench until is it level with the surrounding soil. You can blanch the leeks even further by adding a small hill of mulch or straw around the base of each stalk. You can use soil, but then risk having the stalk rot early. Straw works the best as long as the layer is thick enough to block out the light. Start the hilling process around mid-summer.
The purpose is to lighten the bottom of the stalks. Unlike celery, the blanching is more of a necessity with leeks as only the whitened parts of the stalk are edible.
Keep your leeks well-watered, particularly in very warm weather. If your plants are thriving, the leaves may grow long enough to bend back down to the ground. If this happens, trim the leaves back slightly to prevent any soil diseases from getting up onto the leaves.
Considering their size, and root depth, you would need a large container (at least 5 gallons) to grow leeks. And that would only suffice for one plant per pot. Depending on your needs, its not very practical for any real harvest. But for a few leeks, you can certainly do it.
If the pot isn’t large enough to plant in a “trench”, you can still try to blanch the stalks with a pile of straw or mulch as the plant grows.
Pests and Diseases
The leek moth is a particular problem for this plant, though they also attack onions and garlic. The moth itself isn’t the problem, but the larvae caterpillars. They are also sometimes called an onion miner because of the tunnels they chew in the leaves.
You can keep the moths away from your plants and prevent them from laying eggs on the leaves with a cover of fine mesh during the spring. If you do see small yellowish caterpillars, you can either handpick them or use insecticidal soaps to repel them. They may not destroy your crop, as healthy leek plants should be able to withstand a bit of chewing.
A disease threat to leeks is white tip disease, which is a fungus infection that can develop in soggy soil. A wet, cool summer can bring it on. The tips of the leaves will start to pale, and then wilt. If the leeks are large enough, you can harvest them for use immediately. Fungicide might help with smaller plants, but only if applied soon after it sets in.
White rot is another possible problem, creating thread-like strands of fungus at the base of the plant. You can’t really treat them, so pull up the plants right away to prevent the spread of it. To minimize diseases in your soil, don’t plant leeks or any other onion family crop in the same place for at least 3 years.
Harvest and Storage
You can start to harvest your leeks once the stalks get to be at least an inch thick. Unlike the onions they resemble, you can’t just pull up a leek. Their roots are too sturdy and you will end up snapping the stalk in half. You’ll need a shovel to dig out the plants.
Make sure to harvest your leeks before they get too large. Once they “bolt” or go to seed, they are no longer edible.
Chop off the darker green leaves, and use the white stalk along with the lighter leaves. Some people do use the upper leaves as flavoring for soups or stews but they are not really used as a vegetable.
If you have more leeks than you can use, they will store for several weeks in a cool, dark place (root cellar or basement). Dig up the entire plant, and store upright in a cardboard box. Don’t wash them or cut off the roots.