Growing Leeks

This root vegetable has a mild onion-like flavor, and can be eaten both raw and cooked. Originating from the Mediterranean region, leeks are high in Vitamin K, and also have lots of other nutrients. They make a great addition to soups, stews, roasts, and quiches.


To help ensure your Leeks thrives, we’ve put together this how-to video and transcript covering topics like:

  • Glossary of Leeks terms

  • Varieties of Leeks available

  • Starting your Leeks seeds

  • Caring for Leeks at all stages

  • Fertilizer and/or Mulching

  • Transplanting best practices

  • Companion Plants do’s and don’ts

  • Common challenges and Their Solutions

  • Pests, Diseases and what to do about them

  • Harvesting and storing your Leeks


Glossary of leeks terms

Before we get started, let’s learn a little bit about leeks.


HARDENING-OFF

The process of gradually getting plants used to outside conditions like sun exposure, temperature, and wind. Put seedlings outside for a few hours per day, then gradually reduce their water and temperature until it’s time to transplant.


THINNING

The process of gently removing seedlings at a certain growth stage to leave only the strongest and most mature plants behind.

This encourages them to grow properly and allows your leeks to thrive without any major competition.


BLANCHING

A process where you deliberately cover parts of the plant with soil or a piece of cardboard (like a milk carton). This encourages growth, and keeps leeks from photosynthesizing.

The result? A larger, edible white stem.


DIBBER

A pointy gardening tool that makes holes for transplants. In the case of leeks, these holes would be at a depth of 6 inches.


OPEN POLLINATED

When a plant is able to pollinate itself, and also gets pollinated by wind, insects or by human hand.

A Close Up of Leeks

Varieties of Leeks

A quick note is that although hardy varieties can take up to 100 days to mature, they are able to withstand heavy freezes.


AMERICAN FLAG

Leek: American Flag Variety

This variety has blue-green leaves and is very hardy and cold resistant. The large thick stems will blanch to a clear white.


TITAN


Leek: Titan Variety

An early type with dark-green leaves and white stems.




ARKANSAS


Leek: Arkansas Variety

This variety has dark blue to green foliage and is tolerant to temperatures under the freezing point.


MUSSELBOURGH


Leek: Musselbourgh Variety

Another hardy variety with thick and relatively short stems. Musselbourgh: Another hardy variety with thick and relatively short stems.


Leeks in a Basket

Starting your leek seeds

  • If you plan to grow long-season varieties, you’ll want to start your seeds indoors.

  • It’s important to keep in mind that the ideal soil temperature for leeks to germinate is between 50-75°F (10-24°C).

  • You can start your transplants about 8-10 weeks before the last frost date, sowing in flats that are a half inch deep, and a quarter inch apart.

  • Once your seedlings are 2 inches (5cm) tall, either transplant them into containers or thin them in their current container.

  • If you plan to directly sow outside, plant your seedlings a half inch deep (1.3cm), and space them 1 inch (2.5cm) apart in rows that are about 20 inches (50cm) apart. Then, after your seedlings have sprouted, thin them to 4-6 inches (10-15.2cm) apart.

  • Leeks are fairly easy to grow from seed, and can tolerate standing in the field for an extended harvest.


Caring for leeks

  • We’ll tell you everything you need to know about caring for your leeks. Lean how to water them, their fertilizer and mulch needs, plus transplanting best practices and growing structure options.

  • We’ll also let you know what does and doesn’t grow well with this crop.

  • Before you get started with your leeks, keep in mind that they grow best in soil with a pH between 5.0 and 6.5.

  • Because of their shallow root system, leeks lose water fast – so they need consistent moisture to be at their best.

  • Drought stress during their growth stage will lower their yields, which you definitely want to avoid. So thoroughly moisten your soil once a week at a depth of 18 inches (46cm).


HILLING YOUR SOIL

  • Also, you’ll want to hill the soil around your leeks 2-3 times for blanching purposes. If you only do one big hilling when the plants are still young, it may cause their stems to rot – which is why 2-3 times works best.

  • You can start this process when your plants are roughly the size of a pencil. And if you like, you can also try placing cardboard (like an old milk carton) around your plants.

  • Keep in mind though, that the deeper your transplants were set in the first place, the less you’ll need to hill soil around their stems.

  • Weeds can also be a big problem for your leeks, especially in their first 2 months of growth. That’s because in this early stage, leeks grow very slowly and compete poorly.

  • Make sure to cultivate shallowly, and take care not to damage your plants.

  • The great thing about leeks is that they can overwinter – just as long as your soil is heavily mulched and hilled up around your plants.

Leeks Being Cut

FERTILIZING AND/OR MULCHING

  • Mulch your leeks with grass clippings, wood chips or straw to contain moisture in the soil and to control the growth of weeds.

  • In wintertime, mulch will also protect your leeks from temperatures that are too low.

  • Before fertilizing, check what type you’ll need by using a soil kit.

  • Once you’ve discovered what you need, apply your fertilizer no deeper than 6 inches (15.2cm) in your soil.

  • Also, you’ll want to side dress with a nitrogen fertilizer (21-0-0) in your leeks’ third month of growth.

  • NOTE If you plan to fertilize using compost, apply no more than 1 inch of well-composted organic matter for each 100 square feet (9m2) of your crops..


TRANSPLANTING BEST PRACTICES

  • Transplant crops that have been started indoors when they are about 8 inches tall. After hardening-off, set your transplants 4-8 inches deep (10-20cm), spacing them 4-6 inches (10- 15.2cm) apart in rows that are 20 inches (50cm) apart.

  • You’ll want to make the planting holes about 6 inches deep – and a dibber tool makes this task much easier.

  • Place your transplants in the hole, cover until the first leaf and then let water (either irrigation or rain) fill up the rest.

  • Setting your transplants this deep into the soil reduces your need for hilling - which is a necessary step if you want to blanch your plants.


GROWING STRUCTURE OPTIONS

RAISED BEDS

  • This is the ideal structure for growing leeks. Raised beds have good water drainage, which is important because it helps avoid overly wet soils and bacteria that may cause rotting diseases.

  • These structures are also easy to access, and they prevent you from stepping on or around your plants as you work.

  • This decreases the risk of injuring your plants, and makes for a much more comfortable gardening experience.

  • Plus, because they’re elevated from the actual ground, soil will warm up faster so you can start planting earlier.


CONTAINERS

  • A great space-saving option to use, but keep in mind they should be at least 8-10 inches (20- 25cm) in diameter and have a volume of 2 to 3 gallons (7.5-11.3l) to accommodate the whole plant.

  • Containers are also more flexible to be moved around, which can help you optimize the growing conditions of your leek plants when it comes to sun exposure and watering.

  • They’ll also need holes in the bottom for good drainage, which is essential since water-soaked soil can lead to disease infection.


OPEN FIELD

  • Before planting, check your soil for its fertilizer requirements and existing diseases first.

  • Also, make sure that no other member of the allium family has grown in that planting spot for the past 3- 4 years.

Leeks Growing in the Sun

COMPANION PLANTS DO’S AND DON’TS

DO’S

  • Beets, carrots, celery, onions, spinach are all great companions, as leeks repel carrot rust flies that typically bother these plants.

DON’TS

  • Avoid planting anything from the allium family (garlic, onion, shallots) near your leeks, and also keep in mind that leeks will stunt the growth of beans and peas.

Common challenges and their solutions

  • There are a few pests and diseases that can potentially harm your leeks. Not to worry – we’ve listed them below, plus what you can do to either prevent or fix the problem.


POTENTIAL PESTS

ONION MAGGOTS

They begin as larvae in the soil over the winter, then emerge as flies in the spring. Females typically lay their eggs at the base of the stem, and cool moist conditions increase their chance of survival.


The larvae feed on roots and stems, and the damage they cause can act as an entry point for soft rot bacteria.

  • Solution: Place yellow sticky cards around your plants to attract and trap the flies.


THRIPS

Tiny insects that form silver lines and white patches deep between the leaves where new ones are growing. If the infestation is severe, it can result in the death of your plants.

  • Solution: Use straw mulch to deter the thrips, and practice good field sanitation.

Chopped Leeks on the Counter

POTENTIAL DISEASES

PURPLE BLOTCH

This fungus favors warm and humid conditions. It begins on older leaves as small, sunken lesions, which eventually turn purple to brown, often with yellow rings. The bulbs can also get infected by stem wounds.

  • Solution: Plant disease-free seeds in appropriate spacing to avoid excessive leaf wetness and to improve air circulation.

  • Also, practice crop rotation and also harvest in dry weather.

  • Finally, avoid crop injuries and practice good field sanitation (like cleaning your tools after working in a specific spot in your garden).


WHITE ROT

This disease turns the leaves yellow and causes them to die back, while also stunting your plant’s growth. This disease will really thrive in wet and cool soil conditions.

  • Solution: Plant disease-free seeds from a reliable source when possible.

  • Also, practice good field sanitation by properly cleaning your equipment, hands, and shoes when you work in different parts of your garden.

  • Be sure to remove and destroy any infected plants, but do not compost them since the fungus can survive in crop residue.


FUSARIUM BASAL ROT

This fungus can infect plants at any stage of their growth, causing the curving and yellowing of leaves. Wilting might also happen, and the bulb tissue will be brown and watery when cut open.

  • Solution: Plant resistant varieties, practice crop rotation, and protect your plants from injuries (either from insects, fertilizer, or machines/tools).


BOTRYTIS NECK ROT

This disease typically appears after harvest, during storage. The soft tissue of your leeks will become water-soaked with a yellow discoloration. Also, the bulbs break down into a soft mass, and a grey mold will develop.

  • Solution: Practice crop rotation every three years, and make sure to plant your leeks with ample spacing, which is at least 1 inch apart after thinning.

  • You’ll want to destroy any remnants of the plant after harvest, and avoid injuring your leeks while harvesting and storing them.


NOTE

Fusarium basal rot, botrytis neck rot, purple blotch or white rot can also all occur as storage diseases.

  • Solution: Make sure to check your leeks for any symptoms before you store them. If you find any infected plants, you’ll want to get rid of them.

  • Undercut the bulbs to get rid of every root, and then store your leeks under their ideal conditions, which is at about 32-34°F with 75% humidity.

  • You’ll also want to do your best to avoid bruising or injuring your leeks.

Fresh Grown Leeks

Harvesting and storing

  • Leeks are ready to eat once their stems are at least 1 inch (2.5cm) in diameter. To harvest them, gently twist and pull the stem out of the soil.

  • Looking for different ways to store your leeks? You’ve got options. They can be frozen, pickled, canned or dehydrated.

  • If you’re planning to freeze your leeks, make sure to prepare them properly before sticking them in your freezer.

  • What you’ll want to do is blanch the trimmed leeks for about 2-3 minutes in boiling water, then towel dry and place them in freezer bags.



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