Leeks are a hardy, no-fuss plant that can be seeded outdoors about the time of the last spring frost, though they will survive light frosts even when young—and heavy frosts in the fall. Find out how to grow leeks every step of the way: from sowing and transplanting to harvesting.
If you’ve. never had leeks, they’re a more mild onion that have a sweeter flavor that regular onions. In recipes, leeks may be substituted for onions and, unlike onions, can be chopped and frozen for use in the winter after you run out of your own onions. You eat the white part of the leek, not the green tops.
Leeks can be harvested over a long period if you choose the right mix of varieties. Varieties described as early-season leeks will be ready in time for autumn, while mid and late-season leeks can be harvested through the winter and into spring.
Leeks grow best in soil rich in organic matter, in a sunny, open position. Leave enough space between plants for good airflow. Look out for varieties described as ‘rust resistant’, as this fungal disease can cause minor problems from summer onwards.
When to Plant Leeks
Like onions, leeks started indoors need to be planted early: 10 to 12 weeks in later winter before the last frost date.
Leeks can be planted outdoors about the time of the last spring frost, though they will survive light frosts even when young — and heavy frosts in the fall.
Sowing Leek Seeds
If starting indoors, start sowing the earliest varieties under cover in late winter. To sow your leek seeds, first sieve potting soil into pots or open flats and gently tamp the potting soil down. Sow the seeds about an inch apart in trays or pots, or two seeds per cell in a plug tray. Cover them with a thin layer of more sieved potting soil, and water them. Keep the potting soil moist but not too wet.
Place early sowings on a sunny indoor windowsill or in a greenhouse. You may want to separate the seedlings into individual pots as they get bigger.
To encourage the plants to develop strong roots and a stocky stature, use scissors to give them weekly haircuts. Cutting off all but the bottom 2” of the plant will help force the plant’s energy back into the roots
Our Garden Planner can recommend personalized times for sowing, planting and harvesting your crops in your location using data from your nearest weather station.
Leeks are ready to transplant to the outdoors about the time of the last spring frost and when they are six to eight inches tall. Acclimatize them to outdoors conditions first (a process called ‘hardening off’) by putting them outside for increasingly longer periods over one to two weeks.
Prepare the soil for leeks by lightening it up with lots of compost. There’s no need for much fertilizer.
To plant your leeks in the soil, ‘dib’ holes that are about the same height as the stems of the leek seedlings. You can use a purpose-made tool to do this, or use the handle end of a garden hand tool such as a trowel. Make the holes about six inches apart, with a foot between rows. Alternatively, if you’re planting in blocks space them 7 inches apart each way.
Remove the leeks from their pots. If they haven’t already been potted on, you’ll need to carefully tease the roots apart. Place the seedlings into the holes, making sure the roots reach right down to the bottom of the hole. Fill the holes with water and leave to drain. Don’t fill the holes back in with soil – it will fall back in by itself over time, allowing the leek shanks (stems) to swell and helping to blanch them so they have long white usable stems.
To maximize space, grow quick-growing salad leaves in between your newly planted leeks. These will need to be harvested by midsummer, when the leeks will need the space to grow well.
Water your leeks if the weather is very dry. Keep the ground between the leeks weed-free by hand weeding or hoeing once a week.
Growing leeks in holes will provide a short length of white stem, but for longer white stems you can blanch them by excluding light from the stems two to three weeks before harvesting. Simply draw the soil up around the leeks, or tie cardboard tubes around the stems.
Harvesting and Cooking Leeks
Harvest your leeks as soon as they’re big enough for your needs. Lever it out of the soil using a fork, while pulling up on the leaves. Trim the roots and any damaged leaves onto the compost heap and rinse off the soil.
In very cold areas you may wish to dig your leeks up before the ground freezes solid.
Leeks can be added to many recipes, for instance soups, pies and stir-fries. They also make a delicious side dish by sautéing them with cream and shredded cheese.
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