If you are unfamiliar with leeks, they have a mellow onion-like flavour with no pungency. They are kind of like a super-sized green onion. However, they are not onions.

For growers, leeks are a wonderful, tasty, hardy, attractive vegetable that is fairly easy to grow and won’t bolt.

For consumers, leeks are more versatile than just for leek and potato soup!

It may be helpful to provide some recipes and cooking suggestions for your customers so they can get the most out of their leeks and come back for more!

We will be learning how to grow leeks from market farm experts Pam Dawling (Sustainable Market Farming) and JM Fortier (the market gardener).

Why Grow Leeks?

Unlike onions, leeks will grow independently of day length and will stand in the field at temperatures below what many other veggies can handle.

They increase in size until you choose to harvest them.

This flexible harvest date during winter and fall is advantageous to growers who want a steady supply of produce.

Planting dates depend on your climate.

Varieties of Leeks

Leeks come in two main types: 

1. The less hardy, faster-growing varieties, often with lighter green leaves, which are not winter hardy north of Zone 8. 

Pam likes Lincoln (50 days to slender bunching leeks, 75 days to mature leeks), King Richard (75 days, fast-growing), and Giant Bulgarian.

There is also American Flag (which did not work out well for Pam) and Giant Musselburgh (105 DTM) is bolt resistant, for overwintering in milder climates.

JM uses Varna and King Richard for his summer leeks.

2. Hardier winter leeks such as Tadorna (100 DTM), Jaune du Poiteau, King Sieg (84 DTM) is a cross between King Richard and the winter-hardy Seigfried, and Bleu de Soaize (105 days, very hardy).

JM uses Megaton variety for his winter leeks.

Crop Requirements

Leeks do best in well-draining soil rich in nutrients, with a pH of 6.5 and good sunlight.

Ideal growing temps are 55-75°F (13-24°C).

Growth is slow above 77°F (25°C), but the plants do not deteriorate heat and will resume growth when cooler weather arrives.

Some varieties are hardy to 10°F (-12°C), or even to below 0°F (-18°C) if protected by a one-foot mulch of straw or hay or thick rowcover.

Sowing

Leeks are slow-growing but easy to care for and frost tolerant. 

Seeds will germinate between 52-73°F (11-23°C).

Count back from your expected first harvest date, using the time to maturity (7-17 weeks) in your calculation.

Add 12 weeks for the time from sowing to transplanting to these times, plus 1-2 weeks for the seed to germinate.

Using this method usually means sowing indoors in January, February, or early March.

Seeds may be sown ¼ – ½” deep in open flats, or channel trays at 3 to 4 seeds per inch, or in plug flats in clumps of 4 or 5. 

Seedlings in open flats may later be spotted (pricked out) to 2” apart. This may be more worthwhile for those with a short growing season. 

Harden off the seedlings before the transplant date.

If you have a long enough growing season (zones 6 and 7) and don’t want leeks in summer, you can delay sowing until March.

For simplicity’s sake, Pam and team forego indoor planting and sow in outdoor nursery beds in late March.

They sow ½-¾ “ deep in rows 3” apart, 10’/100’ of the final row at 6” spacing.

As needed, the seedlings are thinned to ½-1” apart and weeded as leeks do not compete well with weeds.

They transplant the leeks in late May or early June, in beds cleared of early spring crops.

Growers with longer growing seasons (zones 8-9a) can plant two crops: the first 12-14 weeks before the last spring frost, and the second in mid-July to transplant in late September or early October.

In zones 9b-11, sow only in July, and use bolt resistant variety for leeks to harvest in the new year. 

If sowing in hot weather, chill the seeds overnight before sowing and keep the seedlings cool but brightly lit.

Spring sowings in hot climates won’t grow very much before pausing for summer.

It isn’t worth tying up space for the length of time they need to size up, while weeding every four weeks as well.

JM and team start their leeks very early in spring. They are among the first seedlings started in the greenhouse.

The purpose of this is because they want their transplant seedlings to grow long.

A deep container is used to allow for increased root development.

They only do one leek seeding per season, but use varieties with different numbers of days to maturity (DTM). 

The seedlings get transplanted into the gardens in early May.

This gives them about 10 weeks to grow to a pencil size thickness and at least 10” long, which is the size they want.

Transplanting

The ideal size for transplanting is between a pencil lead and pencil in thickness.

Pam plants at 6” spacing, with four rows to a 48” bed. 

Growers wanting really huge leeks use wider spacings.

Leeks can also be planted in clumps of four to six at either 10-12” in-row spacing for easier hoeing or at 6” for smaller bunching leeks.

Both Pam and JM use special planting techniques for their transplants in order to develop long, white shanks, which is what your customers are looking for in a leek.

Let’s start with Pam’s method (it’s a team effort):

• Water soil well, more than an hour ahead of time.
• One person makes parallel V-shaped furrows, 3” deep along the bed.
• Next, a couple of people make holes 6” apart in the furrows. You can use hoe handles, dibbles, or homemade from broken digging fork handles for this job, The tool just needs to have a diameter of 1 ½-2”.
• The depth of the holes is determined by the height of the transplants and is likely to be 3” or more.
• Another person digs up some of the transplants from the nursery bed and transfers them to a small bucket containing an inch or two of water.
• Resist any temptation to trim either the roots or tops of the leeks.
• To transplant, take a leek, shake it free from its neighbours, and decide whether to plant it.
• Discard ones that are thinner than pencil leads.
• If the plant is a good size and looks healthy, twirl it as you lower it into the hole to prevent roots from folding back on the plant and pointing at the sky. They need to grow downwards.
• This works best if roots are still wet and muddy from the bucket water.
• Ideally, the tops of the leaves will poke out of the furrow, not more.
• Get the depth of the hole making adjusted to suit the prevailing plant height. This creates the depth for growing a long white shank.
• Surprisingly, you do not need to fill the holes with soil (you do NOT want to bury the seedlings).
• The hole fills naturally as the plants become tall enough to survive the depth.
• Next, someone gently waters each hole, from a low-pressure hose or watering can.

The goal is to water the plant roots, adding only a little soil to each hole.

The shelter of the hole helps the plant get over the transplant shock, and because leeks have slender tough leaves, they do not lose a lot of water by transpiration.

This means that transplanting in quite hot weather is possible, as is transplanting in the mornings.

Keep the soil damp for several days after planting, and give 1” water per week as needed.

Leeks do not compete well with weeks, so cultivate as needed. Hoeing will help fill the holes.

JM’s Leek Transplanting Method:

JM and team bury the seedlings at the transplanting stage.

When their seedbeds are prepared, by broadfork and firmed with the roller of their rotary harrow, they use a gouge to make hoes 1” wide and 8” deep.

In order to make this task more efficient, they had a tool made (punching dibbler) that makes 3 holes at a time while marking the next ones at 6” intervals.

They then take the individual transplants, cut their roots to about one inch, and drop them in the hole, leaving everything as is.

There is about 2” of plant poking up out of the hole.

They don’t fill the hole. Instead, they water the leeks with a garden hose so that a little earth is washed down onto the roots. 

Over time the first few hoeings will fill the pockets as the transplants get bigger.

The result of this work is a guaranteed 8” elongated blanched stem. 

The biggest difference between Pam’s and JM’s method is that Pam does not trim the root of the transplant, and JM does.

You will have to do your own research and experiment to figure out if trimming the root is right for you or not. 

Pests

The leek moth seems to be the leeks only major pest. The larvae of the moth dig tunnels through the shafts, making the veggies unsellable.

Covering the leeks with anti-insect netting when the egg-laying season is in full swing (late August/early September) helps with this pest.

Diseases

Leeks are generally sturdier and less likely to succumb to disease than bulb onions

Leek rust is a fungus that can occur in mature crops in dry weather.

Rust coloured spores appear on both upper and lower leaf surfaces.

Rust can seriously reduce the yield and marketability of the crop.

Harvesting Leeks

Leeks can be harvested whenever they seem big enough.

When harvesting leeks, remember how deep you planted them and try to avoid spearing them.

Put the tines of a digging fork vertically down in the ground 2-3” away from the leeks.

Step on the fork and lever back until the leeks move.

Remove one leek, chop off the roots, invert the plant, and cut the leaves in a V shape, so that the tougher outer leaves are shortest and the younger inner leaves are longest.

Clean up any obviously inedible outer layer, then put the leek in a bucket with about 1” of water at the bottom. This keeps them hydrated before taking them to the cooler.

JM sells his leeks in bunches, the number of leeks per bunch depends on the size.

For presentation purposes, they trim the roots and cut off the tips of the upper leaves in the shape of a chevron.

Storage

Leeks are best stored at 33°F (0.5°C) and 65% relative humidity.

For short-term storage, they can be stored in a walk-in cooler with root ends kept in water.

As well, they can be stored in plastic bags for 2-3 months at the right temperature, or frozen.

Bottom Line

Leeks sound like a vegetable that I would like to grow! They are not in our crop plan for this year, but they are certainly on my list of crops to try next year.

I like that they are fall veggies and do not have many pests that are attracted to them.

Transplanting may take a few tries to get the hang of, but that’s OK,  as we are new to market farming so basically everything will be trial and error for us anyways!

What do you think? Are you going to try growing leeks in your market garden? Let us know in the comments below.

Stay Local,

Kathy & Jon

your friendly neighbourhood growers