Green Man Publishing

Leek

Allium porrum

Introduction: This non-bulbing relative of the onion is native to Eurasia and was first cultivated somewhere in the Eastern Mediterranean. It has been a food of the common people since the ancient Egyptians and still is in many parts of Europe. This is in stark contrast to the United States, where leeks are often considered a luxury food, with prices to match its elevated status. When you start growing your own leeks you soon come to understand why they are so important in French cooking.

Ease of growing: The leek is a satisfying crop to grow and much more straightforward than the onion. It is a biennial so you don’t usually have to worry about premature bolting and it doesn’t produce a bulb so you don’t need to think about day length and its effect on bulbing. It is also very hardy and winter leeks can simply be left in the ground until needed for the kitchen.

Crop value: The leek is not only one of the hardiest of common crops, but also one of the most useful and it was once very important for Northern European peasants. It would supply food right through the winter and still be good in early spring, when little else is available. Its sweet and delicate onion flavor was widely used to flavor more bland staple foods. Of course it is equally useful today and should be considered one of the garden staples.

Climate: Leeks prefer cool (50 – 70°F), moist growing conditions, but also do well in warmer climates if well supplied with water. Many types are very cold tolerant (down to 20°F) and are often one of the last plants standing in a frozen garden.

Leeks will grow quite happily in warm weather (above 75°F, but won’t taste as good as in cooler temperatures.

About Leek  

Seed facts
Germ temp: 40 (60 – 75) 95°F
Germination time: 14 – 21 days
30 days / 41°F
13 days / 50°F
7 days / 59°F
5 days / 68°F * Optimum
4 days / 77°F
4 days / 86°F
Germination percentage: 75%+
Viability: 1 – 5 years
Wks to grow transplants: 10 – 12  

Planning facts
Hardiness: Hardy
Growing temp: 45 (55 – 75) 85°F
Plants per person: 30 – 50
Plants per sq ft: 9  

Planting:
Start: 10 – 12 wks before last frost date
Plant out: On last frost date
Direct sow 4 wks before last frost date
Sow fall crop 12 – 16 weeks before first frost  

Harvest facts
Days to harvest: 110 – 200 days from seed
75 – 100 days from transplants
Yield per plant: 8 oz per plant
Yield per sq ft: 2 – 9 lb sq ft  

Nutritional content: Leeks are a good source of vitamins A, C, K and several B’s, as well as potassium, iron and some beneficial phytonutrients. They are also relatively high in calories, with around 270 per pound.

Soil

pH 6.0 – 7.0

Leeks need a deep, rich, fairly neutral soil. They don’t mind heavy soil, but it should be well-drained, because the plants will often remain in the ground through much of the winter and are susceptible to rot in wet soil.   

Soil preparation: Leeks need rich soil to grow well. A common practice is to plant leeks in soil that was heavily amended and cultivated for a previous crop, such as potatoes. If it is low in organic matter, or particularly heavy, incorporate 3 – 4˝ of compost or aged manure into the top 12˝ of soil.

Leeks do very well in deeply cultivated intensive beds. If your soil is compacted, you might want to consider double digging because (remember) leeks like loose loam. They also like potassium and phosphorus, so add colloidal phosphate and greensand or wood ashes (or an organic fertilizer mix).

If your soil is poor, you might grow them in trenches, enriched with aged manure or compost. This is how they get those prize nine pound leeks.

Leeks can be planted fairly early in the spring, so gardeners often prepare the growing bed the previous fall.

Planning

Where: Leeks need full sun, especially if growing in winter. For best growth they should also be sheltered from cold winter winds.

Leeks take quite a long time to grow and will be in the ground for most of the growing season, so put them where they won’t be in the way. Fortunately they don’t take up much space and are good for intercropping, as their foliage is relatively sparse for much of their early growth.

When:

Spring: Leeks are very hardy and prefer a long cool (not much above 70°F) growing season, so they are one of the first spring vegetables to be started indoors.

Leek seedlings grow quite slowly, so they are usually started indoors, about three months before they are planted out (sometimes as early as December or January). The earlier you start them, the larger they will get. Unlike many crops they don’t get over-mature quickly, they just get bigger. The seedlings are transplanted outdoors on the last frost date (after being hardened off.)

Leeks can also be direct sown, about a month before the expected last frost, or as soon as the soil can be worked. The protection of cloches or poly tunnels will speed up growth.

Some people start leeks both indoors and outdoors. The transplants are for eating over the summer, while the direct sown ones are for using the following winter.

Fall: In areas with mild winters, leeks are best grown as an over-wintering crop. They are started in early summer (indoors or out) and can be harvested as needed through the winter. Any plants that are left by spring will put on a burst of growth and then bolt.

Planting

Transplants:

Starting inside: Leeks transplant easily so are usually started in flats. They don’t have much foliage so can be planted quite close together and you can get a lot of plants in one flat. The seeds germinate and grow slowly, so start them early, water regularly, feed occasionally and be patient. They should be ready to plant out in 8 – 12 weeks when they are about 8˝ tall and about ⅛˝ in diameter. Some people advise trimming the tops and roots, to make planting easier (they can get quite long and easily fold up in the planting hole).

Hardening off: If spring transplants are to go outside while it is still cold, they should be hardened off first. You do this by putting the plants outside for 2 hours on the first day, then 4 hours on the second day. Add 2 hours every day for a week and then plant out.

A simpler alternative is to put them in a cold frame, which is opened for longer periods each day and closed at night.

Planting out: There is no point transplanting the seedlings outside before the soil has warmed up, they will grow faster inside. Wait until a month after the last frost date.

In my opinion the only way to plant leek seedlings is with a dibber. In fact a desire to plant a lot of leeks is a sufficient reason to get a dibber (or make one out of a broken spade, shovel handle or piece of stick). Mark out the required 4 – 6˝ hole depth (depending on size of plants) on the side of the dibber, so you know how deep to go.

To plant you simply punch a series of holes in the soil and drop a plant into each hole. When you have planted a good sized section you water them all with a trickle of water. There is no need to fill the hole, enough soil will wash down into the bottom to cover the roots. It couldn’t be easier or quicker.

You can also transplant the seedlings into a 6 – 8˝ deep trench, Plant with a dibber as described above and when the plants are growing well gradually fill the trench with soil. This blanches the stems and provides a greater length of the desirable white stem.

Leeks can also be planted in a row on level ground. They are then hilled up as they grow, to blanch the lower stems.

Starting outside: Fall leeks are often started outdoors in a nursery bed and then later transplanted to a permanent site. This is much more space efficient than direct sowing and the seedlings are more easily protected from pests.

Direct sowing: Summer leeks can be direct sown in early spring at a depth of ¼ – ½˝. Space the seed ½˝ apart and gradually harvest thin to the desired spacing.

There are a couple of problems with direct sowing into the beds. One is that it wastes bed space because they are so slow growing. Another is that you have to find another way to blanch the stems. To do this you either have to sow the seed into a trench as described above, or you earth them up with soil (see Blanching below for more on this).

Spacing:

Beds: Leeks are usually planted in offset rows across the bed. The spacing ranges from 3 – 6˝ depending upon the fertility of the soil (to get the highest yield of large plants space them 6˝ apart). You might want to use a wider spacing, so you can get a hoe between them for weeding.

Rows: When you plant in rows it is easier to earth them up. Space the plants 2 – 6˝ apart in the row, with 12 – 24˝ between the rows. If you use the closer spacing align the plants so the leaves point perpendicular to the row (leek leaves always emerge opposite each other).

Care

Leeks need looking after carefully, because they grow slowly and don’t have a lot of foliage (a newly planted leek bed actually looks pretty pathetic). They should always have an abundance of available nutrients and water for best growth.

Weeds: The lack of foliage makes young leeks vulnerable to competition from weeds. It is especially important to keep them well weeded when they are young and spindly, as they don’t shade the soil very well (or compete with weeds). They are quite shallow rooted, so be careful when weeding with a hoe (it’s safer to hand weed).

Water: Leeks grow best in moist soil, so make sure they have a constant supply of water. Water them deeply once or twice a week. Don’t over water though, as this can encourage disease problems.

Fertilization: Leeks are often in the soil when it’s cold and nutrients aren’t readily available. It helps to give them a feed of compost tea or liquid kelp, as soon as they are well established.

If the soil isn’t very fertile you should feed them every 4 weeks until late summer and then stop (later feeding can make them more susceptible to cold damage).

Mulch: Mulch is very beneficial for leeks. Their lack of foliage means that the soil is prone to drying out in sunny weather and a mulch shades the soil and helps it to retain moisture. It also helps to keep down weeds and is a source of nutrients for the soil.

In areas where winter temperatures drop well below freezing you should protect the plants with a deep mulch. It not only protects the plants from cold, but also stabilizes the soil temperature. This prevents frost heaving, which can damage the roots. It’s best to apply this in fall while the soil is still warm.

Blanching: Leeks are often blanched (deprived of light) to get a longer area of white stem, as this is considered superior to the green part.

Blanching is usually done with soil, either by earthing up the stems, or filling up the trench they are growing in. Some gardeners wrap corrugated cardboard collars around the plants before blanching, to prevent soil getting lodged between the leaves (no one likes gritty leeks). You can also blanch the stems with a deep mulch, which has the advantage of not being gritty.

Pests: Theoretically leeks are susceptible to the same problems that afflict the related onions, but generally they are quite pest free. They are occasionally bothered by onion maggots or thrips (see Onions).

Diseases: Leeks may be affected by the same diseases as onions, including botrytis, purple blotch, white rot and downy mildew. Most of the time they tend to be remarkably healthy though.

Harvesting

When: Leeks can be harvested as soon as there is enough to be worth eating. If you plant more thickly to start with, you can harvest thin to the desired spacing, without eating into your leek harvest.

The main harvest comes when the stems are ¾ – 1˝ in diameter, though their flavor and texture generally stays good even when they get bigger than this. Leeks only really deteriorate when they start to bolt, as they develop a woody inedible core. If you really want to use bolting leeks remove this before cooking.

How: In loose soil you can sometimes harvest leeks by simply pulling them out of the ground. If the tops break off before they come free, you will have to loosen them with a garden fork first.

If you are harvesting leeks before they reach full size, you should harvest alternate plants, as this gives the remaining plants more room to grow. Just be sure you don’t disturb their roots. Alternatively you could take the largest plants first, leaving the others to size up.

Storage: Leeks are so hardy they are usually stored in the ground and harvested as needed (cover with mulch in cold climates). The outer skin may turn somewhat slimy in very cold weather, but the interior will be fine.

You can store leeks for several weeks in a plastic bag in the fridge. In very cold climates you can store them in a root cellar at 32 – 40°F. Trim off the excess tops and roots and plant them in a box of damp sand.

Seed saving: It’s easy to save leek seed, simply leave the best plants in the ground instead of eating them. Save the seed from at least 12 plants to ensure enough genetic variation. Leeks are biennial and will produce their spectacular flowers in spring (and ripe seed in early summer).

Leeks are cross-pollinated by insects, so you don’t want any other varieties flowering within a mile. In most cases this isn’t likely as few people allow their leeks to flower, If it is possible then you could cage the plants.  

You may want to dig the seed-leeks from their bed while they are dormant and move them to a more convenient location. This frees up the bed they were growing in for another crop.

Unusual growing ideas

Multi-planting: You can plant leeks in clusters, rather than as single plants, simply plant 4 or 6 seeds together. This is usually done in soil blocks, but could also work in flats or cell packs. These clusters must be spaced further apart than single plants to give their roots more room and prevent crowding.

Ornamental: Leek flowers look a lot like ornamental Alliums and aren’t out of place in the ornamental garden.

Vegetative propagation: After leeks flower they produce offsets at the base of the stem, which will grow into new plants. These are known as leek pearls and can be used for propagation or eaten.

Competitive gardening: In parts of Britain the cultivation of the biggest and most perfect leek is a very competitive activity. It results in monster leeks weighing 9 lb or more. I find it amazing how humans can turn even the most unlikely activity into a competition!

Perennial: Leeks can be treated like perennials, as they propagate themselves vegetatively by means

of offsets. They can also self-sow.

There is also a perennial leek (the Babbington leek), which produces bulblets on the flower head instead of flowers. These can be used for propagation too.

Varieties

These differ in their hardiness, time to harvest, color and size of stem. In North America the choice of leek varieties has been quite limited until recently. Fortunately many European varieties are now becoming more widely available. Leeks can be divided into two kinds (can’t everything), according to their hardiness: the summer leeks and the winter leeks.


Summer Leeks: These fast growing leeks aren’t as hardy as the winter types and don’t store as well. They are grown in summer for immediate consumption.

Gros Long d˝Ete

Runner F1

Megaton F1

King

Richard

Varna

Winter Leeks: These leeks grow quite slowly, but are very hardy and can remain in the ground over the

winter. They often have a bluish tinge to their leaves and are considered the best flavored types.

Alaska

American Flag

Bandit

Bleu Solaise

Carenton

Giant Musselburgh

Lyon

St. Victor

Tadorna

Scotland

Kitchen use:

Leeks are considered one of the finest flavored members of the onion family and are especially highly esteemed in France. They are a main ingredient of the famous leek and potato soup (made from two peasant staples).

In France the dark green parts are often used separately to make soup stock.

Leek and potato soup  

4 leeks
1 onion
1 lb potatoes
½ tsp sea
4 cloves garlic
4 cups vegetable stock
2 tablespoon olive oil
2 tsp rosemary  

Chop the leeks and onion and sauté until they become translucent. Add
the chopped garlic and cook another minute. Add the potatoes (chopped
into ½˝ cubes) and the vegetable stock and simmer for 20 minutes in a
covered pan. Allow the soup to cool so you can put it in a blender along with the rosemary and salt and blend until smooth. Re-heat before
serving.  

Elephant Garlic

Allium scorodoprasum

An elephant garlic bulb look like a giant garlic and is even divided into a number of cloves, but it is actually more closely related to the leek than it is to garlic. Its flavor is garlic-like, but a lot milder.

Elephant garlic is a hardy and easy to grow plant (just treat it like big garlic). Plant the large cloves 3 – 4˝ deep and 8 – 10˝ apart, in rows 18 – 24˝ apart.

If any flower stems start to emerge, remove them so the plant devotes all of its energy to bulb production. Unlike garlic the flowers will produce seed if left to their own devices.

Elephant garlic is not a substitute for garlic and if you use it like that you will be disappointed. It isn’t a very important flavoring because the flavor is very mild. You can use it in any of the ways you might use a sweet onion. It is best used raw, to add a mild garlic flavor to salads and sandwiches. It is good on pizza and can also be sauteed, but be careful not to overcook it, as this will make it bitter.