Do you grow leeks in your vegetable garden? If not, you might want to give it a shot!
Leeks belong to the allium family, which also includes things like onions, garlic, and chives. While these crops are incredibly common in the home garden, leeks are often relegated to the grocery store produce aisle. Yet, in my experience, leeks are no harder to grow than any other allium.
In this article, I’ll walk you through three different strategies for cultivating and designing companion plants for leeks.
What Is Companion Planting?
Companion planting is a common gardening practice where different kinds of plants are grown together in the same area. This method is often used to lower the number of pests, improve the soil, and generally make your garden function better.
Think about it: Monocropping (or growing just one type of plant) is relatively rare in nature. Instead, the healthiest ecosystems tend to be those that contain the widest variety of plants.
Companion planting in the home garden can increase the biodiversity not just of plant life but also of wildlife. Growing a number of different plants is the best way to attract beneficial insects, birds, and even soil-borne microorganisms to your garden. And all of these creatures help support a healthier garden overall.
How to Companion Plant with Leeks
There are countless ways to use companion planting in the garden. However, I’ve found that the best results tend to come from choosing a specific strategy based on your goals and sticking to it.
Regarding growing leeks, the right companion plants can make a big dent in the local pest population or extend the season by several weeks. You can also use compatible plants to make your garden more attractive throughout the year.
Natural Pest Management
Leeks are susceptible to the same pests as onions, garlic, chives, and other members of the allium family. These pests include thrips, onion maggots, and leafminers.
Many gardeners turn to companion plants to deter pests and unwanted wildlife. And, to be fair, some plants do repel certain insects. However, the most effective way to control pests in your garden is to instead focus on increasing the number of beneficial predators.
This is surprisingly easy to do just by growing plants that benefit desirable insects (e.g., by providing a food source or shelter). If you’ve ever grown milkweed to support your local monarchs, you’re already very familiar with this concept!
To effectively control leek pests, you first need to know a bit about them and their natural predators:
Onion thrips (Thrips tabaci) are tiny insects that suck sap from the leaves of leeks, causing yellowing and physical damage.
One natural predator of the onion thrip is the green lacewing (Chrysoperla spp.). Green lacewings are beneficial insects whose larvae feed on a number of small pests, including aphids, mites, and thrips. Drawing lacewings to your garden will help control the thrips attacking your leeks.
Western flower thrips (Frankliniella occidentalis) are another small insect that targets leeks. They feed on the foliage, causing physical damage, and can also transmit infectious plant diseases.
Predatory mites are a key enemy of the western flower thrip. According to the University of Maryland, these mites feed on the eggs and larvae, helping to naturally control the thrip population.
Onion maggots (Delia antiqua) are small, white fly larvae that burrow into the base of allium plants, including leeks, causing the vegetable to rot.
Birds, parasitic wasps, and ground beetles all help control onion maggot populations. Parasitic wasps and ground beetles target the young larvae. Meanwhile, native birds will feed on both the maggots and the adult flies.
Allium leafminer (Phytomyza gymnostoma) larvae live inside of and eat the leaves of many plants. Infested leeks will suffer from poor health and low productivity.
Parasitic wasps manage leafminer damage by laying their eggs inside the pest’s larvae. When the eggs hatch, the young wasps then feed on the leafminer larvae.
Succession planting is a great way to make the most of a vegetable garden. The basic idea is to plant veggies that mature at different rates during different parts of the year within the same bed.
Leeks are a cool-season crop and grow best when planted in the spring or fall. In warmer climates, you may even be able to grow leeks through the winter!
Leeks also have a long growing season (100–120 days on average). So they pair well with faster-growing crops that can easily be planted and harvested while the leeks mature.
Combining edible and ornamental plants together in one bed will make your garden both functional and attractive. Some gardeners call this technique ‘edible landscaping’. It’s also a key facet of cottage-style gardening.
I like to place leeks toward the back of these types of beds. The leaves — and flowers, if you allow the leeks to bloom — create a taller backdrop for other flowers and foliage.
Best Pest Control Companion Plants For Leeks
Dill: This fragrant herb is a favourite of lacewings and several species of parasitic wasps. Some gardeners also believe that growing dill and leeks together will improve their flavour.
Cosmos: Cosmos are colourful tender perennials that draw in a wide variety of pollinators, including the extremely beneficial green lacewing. Toward the end of the season, cosmos seeds also provide an excellent source of food for maggot-eating bird species.
Sweet Alyssum: Sweet alyssum is a very charming groundcover that handily suppresses weeds in ornamental and food gardens. The small flowers attract mature lacewings, who will then lay their eggs on leeks and other nearby food crops.
Aster: The aster genus boasts daisy-like flowers that are native to North America. Aster plants attract local pollinators to the garden and provide a valuable food source for lacewings and birds throughout the year.
Parsley: Parsley is an easy-to-grow culinary herb that attracts parasitic wasp species. It tends to grow well with all types of alliums and may benefit from the leeks’ pest-deterring properties.
Native Plants: The best way to attract helpful predatory mites to your garden is to incorporate a naturalized border featuring native plant species. This may include grasses, flowers, herbs, and more, depending on your area.
Clover: Ground beetles are handy little critters that thrive in more naturalized garden beds. You can increase the number of beetles around your leeks by including protective groundcover plants like clover. Clover also helps fix nitrogen from the air into the soil.
Rudbeckia and Echinacea: Also known as black-eyed Susan and coneflower, these tall perennials are frequently planted in pollinator gardens. The seeds feed various bird species from late summer through winter.
Best Leek Companions for Succession Planting
Radishes: Radishes mature super fast, with many varieties needing just 4 weeks from seed to harvest. You can plant radishes in early spring or fall at the same time as your leeks. The radishes will be ready well before the leeks begin to fill out and take up space.
Carrots: Carrots are another vegetable that can go in the ground with your leeks. The carrots will be ready to harvest several weeks before the leeks. Alliums also supposedly deter the carrot root fly, which is a common pest of carrots and related crops.
Celery: Growing celery and leeks together can help consolidate garden chores since both crops need plenty of water. Celery and leeks have very similar growing seasons, so planting and harvesting can also be done at the same time.
Spinach: Spinach is a great bookend for either side of the leek growing season. This leafy green typically needs just 3 to 4 weeks to mature and won’t mind growing in the same soil as a recent leek crop.
Lettuce: Lettuce is another fast-growing vegetable you can plant before your leeks in early spring. Most varieties take 4 weeks or more to mature, so you may need to interplant the two. But the lettuce will be ready to harvest when the leeks are still young.
Brassicas: The brassica family includes veggies like cabbage, broccoli, and kale. Few pests and diseases affect both alliums and brassicas, so you can safely grow them side by side in your garden. Just be sure to use fertile soil.
Best Leek Companions for Edible Landscaping
Marigolds: Marigolds are easy to grow and not too picky about their environment, so you can tuck them into your edible landscape wherever there’s room. The red, orange, and yellow flowers will contrast beautifully against more subdued plantings.
Fennel: Fennel is an excellent choice for adding a unique texture to a decorative herb garden. It produces yellow flowers that are both edible and visually appealing. Plant fennel toward the rear of the garden with your leeks.
Swiss Chard: Swiss chard boasts purple, red, yellow, or white stalks topped by green leaves. This leafy vegetable adds some much-needed colour to cottage-style landscaping.
Borage: Borage has blue flowers and a fern-like texture. This edible herb is most commonly grown as an ornamental and is a great companion for leeks and other crops.
Pansies: These cool-weather flowers look great along the front edge of a naturalized garden bed. While technically edible, most people grow pansies for their charming appearance.
Worst Companions for Leeks
You shouldn’t grow onions, garlic, chives, or shallots in the same part of the garden as your leeks. This makes it incredibly easy for pests to find your alliums and can also cause diseases to quickly bounce from plant to plant.
For the same reason, it’s also a bad idea to plant ornamental alliums next to edible members of the onion family.
Asparagus is commonly listed as a poor companion for leeks. The asparagus supposedly interferes with the leeks’ growth. While these claims seem to be based entirely on anecdotal evidence, there’s really no reason to plant these two vegetables together in the first place.
Legumes like beans and peas may have allelopathic properties when grown near leeks. In other words, the beans and peas release biochemicals that prevent leeks from growing to their full potential.
Herbs that prefer dry conditions — e.g., sage, rosemary, lavender, and thyme — tend to suffer when grown with moisture-loving crops like leeks. These herbs can be grown nearby but should be planted in separate containers or raised beds for the best results.
Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.