How to Grow Great Leeks
Allium ampeloprasum, Porrum group biennial
The edible part of the leek is the bottom portion of the stem. The gardener who gives care and attention to how leeks are grown can deliver a much larger edible portion of the stem to the cook.
In most parts of the United States, leek seeds can be started midwinter. If you live in an area with mild winters you have the option of sowing your seeds anytime from April through August. Leek seeds are easier to sow inside in trays than outside in the garden, because garden sown leeks require a lengthy period of weeding that can be avoided by starting the seeds inside. Leek seeds can take 2-3 weeks to germinate. The small plants can be held in trays up to three months, until they are about the thickness of a pencil.
When you are ready to transplant, choose a location in full sun with soil that has ample organic material and good drainage. Add aged manure or compost to the soil if you are in doubt.
Planting leeks is a fairly carefree task. Make holes 6" deep in the soil every 4" with a dibber (a pencil will also do), in rows 12" - 18" apart. Drop seedlings into the holes and water using water mixed with a nitrogen fertilizer such as fish emulsion. It is not necessary to close the hole around the shaft of the leek. The soil surrounding the seedling will protect it from the sun and the all-important crown will rise above the soil. Rain will eventually make the surrounding soil fill the hole.
Once the leeks are transplanted you should keep the bed as free of weeds as possible. You may also hill up soil around the lower stem. Keep the hilled soil beneath the crown so it does not enter the plant. If you skip this step you will still have perfectly acceptable leeks, but hilling in these early stages helps elongate the stem and increase the length of the edible portion of the plant. Keep the plant well watered and fertilize occasionally, especially during the hottest summer months.
When winter approaches, mulch generously around the base of the plant up to 12". As long as your plants stay healthy, you can leave them in the garden and harvest as needed (note: they are not frost tolerant without protection). Alternatively, you can protect your leeks by covering them with a wire supported row cover. By the spring following the year when you planted them, the plants may send up a flowering stalk, indicating it is going to seed. If you cut this stalk and fertilize, the leeks will stay edible even longer.
If you don't fancy digging leeks from the garden in midwinter, you may also dig them out just before the ground freezes and heel them in in a cold frame making certain to leave some roots attached. If a cold frame isn't available, try a five-gallon bucket with about 1" of soil, vermiculite, sand or sawdust at the bottom. Store them vertically, packed into the bucket, and keep the bucket in a cold location that is just above freezing, such as a darkened garage or cellar. Stored this way, your leeks will keep six weeks or longer.