Harvest Leeks for Longer With Successional Sowings

6 June 2013, written by Barbara Pleasant

In active kitchens like mine, there is a constant demand for onions. Fortunately, the garden is able to provide as many bulb onions and shallots as I can grow, and I have plenty of spring onions in spring and fall. But still there are gaps, which are filled quite nicely by growing leeks (Allium ampeloprasum), truly ancient alliums that have been found in Egyptian tombs. From three sowings – one indoors in February, a second sowing outdoors in June, and a final seeding in August – I have fresh, tender leeks from the garden about four months out of the year.

Starting Leek Seeds in Summer

If the only leek seedlings you have grown were indoors under artificial light, you are in for a happy surprise with summer-sown leeks. Like other types of onions, leek seedlings started indoors in late winter are painfully slow to grow until spring brings more abundant light, at which point things turn for the better. Summer-sown seedlings get all the light they can handle from the beginning, so they are much faster and easier to grow. Upright and sturdy, outdoor-grown leek seedlings do not mind crowding as long as they get plenty of sun and are never allowed to run dry. I like to keep my leek seedlings under a small translucent patio table on my deck, where they are shielded from searing sun or thunderstorms.

Three Successive Sowings

In my climate, the first sowing of leeks (started indoors) is ready to harvest in early summer, and there is no point in leaving leeks in the ground once they have reached prime conditions. As soon as leeks reach usable size, start eating them, because there are risks to allowing overripe leeks to sit in the garden. Leeks that have been exposed to cold weather (as is typical with spring seedlings) will often develop a flower spike that alters the structure of the center of the leek, making them less usable in the kitchen.

Mature leeks often begin propagating themselves vegetatively, too, by forming divisions. This process often begins with the appearance of small plantlets that grow on the outside of the shank or "bulb." Later, larger plantlets emerge from the stalk itself, a messy process that involves a rupture in the side of the mother leek. If you have heard of growing leeks as perennials, in clumps, this is how it happens.

There is nothing like a nice stand of leeks in the fall garden, but growing leeks for fall requires that I start seeds in early June, and set out the seedlings when they are about six weeks old – or older. Leek seedlings are surprisingly tough, and willing to wait out early potatoes or other spring crops for their place in the garden.

In July, when I set out my summer-sown leeks, I also plant my final round of leek seeds so I will have seedlings to set out in fall for growing through winter. Leeks are generally regarded as hardy to around 10°F (-12°C), but they will survive colder winter conditions if you cover them with a row cover or perforated plastic tunnel. In my Zone 6 garden, leeks set out in early fall survive winter with ease with nothing more than a blanket of mulch to reduce soil heaving.

Lessons From Growing Leeks

As a garden cook, I have never thought well of the practice of growing leeks in trenches that are gradually refilled with soil or mulch. This guarantees dirty leeks that must be cleaned and cleaned again, so I suggest blanching leeks with tubes cut from paper towels, slit down the side. Or don’t blanch them at all! If you always have new crops of tender, young leeks coming on, you won’t care if the shanks are long or short, thick or thin.

In my garden, leeks are a come-and-go crop that is easy to slip in before or after other veggies. A tight little planting of twenty or so leeks requires only a few square feet, and the plants care for themselves once established. Let there be leeks!