Normally you should be starting leeks for your vegetable garden fairly soon (in February in most climates, so get those seed orders in!). Leeks can and should be planted out about 3 or 4 weeks before the last frost date, as they do best when they start their season in cool conditions and they are not harmed by frost. And normally, you’d harvest them in the fall, after the first frost, since cold intensifies their taste. Then you’d repeat the same treatment, year after year. But not if you’re a laidback gardener: a good laidback gardener only sows his or her leeks once.
That’s because the leek is actually a hardy perennial (“winter leeks” are especially hardy selections, tolerating down to USDA zone 2!). So if you don’t harvest yours in the fall, it will still be alive and thriving in the spring and in fact, will actually beautify your vegetable garden with its lovely globes of pale pink to white flowers. Then it divides, forming a clump of plants. The second fall, therefore, you only have to harvest a few stalks from each clump, leaving the others in place for future generations. Over time, you’ll get bigger clumps and bigger harvests.
The first year, I suggest you sow twice as many leeks as you need. That way you harvest half the traditional way, that is to say, in the fall, and leave others alone so that they perennialize and become the source of your future annual harvest.
By the way, when your “colony” is well established, you can also harvest some leeks at snowmelt, which therefore gives you two harvests per year, one in fall, one in earliest spring! You’ll discover that spring leeks are the tastiest, because cold brings out their sugars. Just make sure to harvest them early, for as soon as the flower buds form, the plant becomes tough, in fact almost woody, and loses its taste.