Leeks are a member of the onion family, and so essential to my notion of a vegetable garden that they are practically a member of my own family. We use them in salads, soups, pies, or braised on their own as a vegetable dish.
Leeks go in the third part of our rotation, planted among the root crops—with a little extra compost or well rotted manure—as they, like onions, are actually as much a leaf crop as a root crop.
We start two plantings. The first, for late summer and early fall harvest, is sown in seedling trays ten to twelve weeks before the last spring frost, to be set out two months later. For the largest leeks, use a cell tray or soil block, and sow two seeds per cell or block, thinning to the strongest seedling after emergence. At planting time the seedlings should be six to eight inches tall.
Prepare the bed, and then, using a dibble or broom handle, poke holes four to six inches deep, six inches on center, or every six inches in rows a foot apart. Drop a plant into each hole, then water them in. Don’t fill in the holes; that will happen naturally over the course of the season as rain erodes the side of the holes.
The plants should just be showing their growing tip at the surface of the soil; if they are not tall enough, fertilize the seedlings and delay planting, or make the holes shallower. The bigger the seedling, though, the bigger the leek and the deeper the hole, the more usable stem you’ll have at harvest time. If the seedlings are grown in open trays and have to be broken apart for transplant, be sure to trim the tops to bring the root and leaf masses back into balance.
We direct-seed the second crop—our overwintering leeks—outdoors about a month before the last frost, sowing the seed 1/4 to 1/2 inch deep in rows only six inches apart, in a spare corner of the root crop bed. We let them grow along there, weeded but not thinned (since we want them to stretch out) until the early peas are harvested. Once the pea trellis have been dismantled, we renew the bed and dig a four- to six-inch furrow right were the peas were, and sprinkle a light layer of compost in the bottom. Into this we set the plants, which have been gently dug from their nursery row, had their roots and tops trimmed back one-third, and been sorted so that the biggest, healthiest plants are used first. Then we lay the plants in the furrow, upright, every six inches. Working back down along the row, we set them into the compost and firm them in a vertical position. As soon as all the plants are in we irrigate, but we do not fill in the trench.
After the leeks are actively growing we gradually fill in the trench, always keeping the level of the soil just below the first leaves, in effect challenging the stem to outgrow our cultivation. Once the trench has been completely filled, so that the ground is again level, we take the excess soil from the edges of the bed (where, in spring, we had interplanted spinach or some other crop) and use it to hill the leeks further. By the arrival of hard frost the stems should be fully banked up and ready to endure the winter without further protection.
For mid-winter harvests in cold climates, it makes sense to mulch the plants though, just to keep the ground from freezing so they can be easily dug. We have found that one of the quonset trellises placed over the leeks and then filled with fall leave (an capped with a bit of plastic to keep the leaves from packing down) works quite well.
We have had no insect or disease problems with our leeks, but we are quite scrupulous about rotating them from plot to plot each year and making sure that they have everything they might need to grow as quickly as they can. All in all, they are trouble-free, even if slow to mature.
Leeks can be harvested at any stage, and in fact baby leeks—the thinnings from the row—are considered a delicacy and bring such a high price in the markets that many commercial growers plant them solely for the restaurant trade. Overwintered leeks must be harvested in the spring before they begin to produce a seed stalk, as the shafts become quite fibrous at that time and are worthless for the table, though the flowering plants are quite beautiful.
Some early leek varieties we have had good luck with are King Richard, Tivi, Pancho, and Titan. For overwintering we grow the old heirloom French cultivar Blue Solaise, though we have also had good harvests with newer strains like Arkansas, Laura, and Furor. King Richard has long been the standard for baby leeks.