We recently talked about companion planting on a pretty large scale when we explored food forests. Today, we are going to look at companion planting on a smaller scale: in your annual vegetable garden. At any scale, companion planting results in less work for the gardener (that's you!) because other plants have taken care of the pollinating, pest management, weed suppression and soil improvement for you. The right companion plants can also increase your crop production, give you better tasting crops and beautify what is often a utilitarian part of your garden. Extra bonus points if those companion plants are also edible. So let's look at all the ways you can use companion plants in your veggie garden, along with a few in-depth examples that really work.
Plants to Attract Pollinators
The most well known companion plants are the ones we use to attract pollinators. A good chunk of the crops we grow in our veggies gardens are actually fruits, and they need to be pollinated in order to produce (think tomatoes, peppers, eggplants, cucumbers, squash, melons and more). When we add plants that are irresistible to pollinators, they can't help but check out the neighbouring flowers of our veggie garden when they visit. Remember that pollinators aren't restricted to just honey bees. There are scads of other pollinators in our gardens: solitary bees, moths, butterflies and other insects too. When selecting pollinator plants, think about when (and for how long) they bloom compared to when your veggies are blooming. Pollinators can't notice flowers that aren't in bloom.
Besides annual companions planted in among your vegetable beds, you can also harness the power of perennial pollinator friendly plants that are situated near the vegetable garden. I have bee balm and hyssop nestled right beside my raised veggie beds to attract tons of bees and to be harvested for tea.
Annuals that attract pollinators: Borage, pansy, alyssum, buckwheat, poppy, zinnia, geranium, petunia, tansy, calendula, cosmos, sunflower.
Perennials that attract pollinators: Bee balm (Monarda), lavender, echium, perennial sage (Salvia), perennial sunflower (Heliopsis), coneflower (echinacea), hyssop, oriental poppy, aster, sedum, yarrow.
Borage (Borago officinalis) is one of my favourite additions to the veggie garden. It is a super easy to grow plant that can get pretty big (2' wide x 3' tall) so make sure you give it some space. It produces fantastically blue star shaped flowers that are absolute bee magnets! Mine are consistently covered in bees. The flowers are also edible, tasting lightly of cucumber. They are a great addition to drinks (try them frozen in ice cubes) and salads, and spectacular candied on cakes. The leaves are fuzzy and can be cooked and eaten like other greens. Be aware that borage readily self seeds in the garden. This is good, in that it saves you buying and starting seeds each year, but it does mean some maintenance in removing seedlings that randomly pop up. Good thing they are easy to identify by their fuzzy leaves.
Plants for Pest Control
There are three major categories of companion plants used for pest control in the vegetable garden: plants to repel pests, plants to distract pests, and plants to attract pest predators. A good starting point is to consider the pests that have bothered your veggie garden in the past and choose companions that will assist with those particular pests. Some plants help out with more than one pest and many of them are edible as well. Adding multi-use plants will save space in your garden.
Plants to repel pests
Many of these are smelly plants. They ward off pests with their bitter, strong smell and taste. In my garden, cabbage moths and their caterpillars are the bane of my existence. I plant a lot of brassicas every year that can get decimated by this pest. Cabbage, of course, is always hit hard, but my kale seems to be their absolute favourite. Yes, good old row covers help immensely, but sometimes life happens and I just don't get them on in time. That's when pest repelling companion plants come to the rescue! Almost all the culinary herbs help with cabbage moths including sage, rosemary, mint, thyme, savory and oregano. The medicinal herbs also help: chamomile, tansy and hyssop. I make sure to plant these liberally all around my cabbage moth prone crops. Celery is also known to help, so I situate that alongside my kale too.
Flea beetles are another annoying pest in my garden. I use a little bit of a different approach for them. I interplant dark, bitter greens in between each plant that gets attacked by these little guys. My favourite is a burgundy coloured lettuce such as Merlot, Fortress, Scaramanga or Darkness checker-boarded between my bok choy, which is always hit the hardest. The bitter taste seems to be working well at keeping down their numbers. The dark lettuce is also a great addition to our salads.
The members of the onion family (garlic, onion, leeks, scallions and chives) are a great all-purpose pest repellent. As you can imagine, that sulphurous odor isn't appealing to most insects and slugs. Randomly scatter these guys throughout your vegetable beds to keep away almost anything that wants to munch on your plants (including rabbits and deer). Here are some other additional pest repelling companion plants, sorted by pest:
Nematodes: marigold
Carrot rust fly: onion, garlic, parsley, rosemary, sage
Root maggots: scallion
Cabbage moth: rosemary, mint, sage, thyme, summer savory, celery, hyssop, garlic, oregano, tansy, thyme, chamomile, tomato
Slugs: mint, dry rosemary, wormwood
Flea beetles: garlic, dark bitter greens, tansy, spearmint, fennel
Tomato horn worm: garlic, dill, basil, borage
Ants: mint, tansy, garlic, catmint
Aphids: tomato leaves, basil, spearmint, stinging nettle, garlic, onion
Cutworms: tansy
White fly: nasturtium, basil, lavender
Asparagus beetle: marigold, parsley, tomato
Plants to distract pests
These companion plants are often known as trap crops or sacrificial plants. We plant these so that pests go right to them; they are their absolute favourites. As a result, less desirable plants that we enjoy eating and that are typically affected by those pests are left alone. Unlike the repellent plants, we don't want to intersperse these throughout the veggie garden. Instead, we want to plant these either along the edge of our favoured plants or off to the side. Keep in mind that the trap crops may get completely chowed upon. Make sure you are mentally prepared for this ahead of time.
I use radishes for this purpose in my garden. Flea beetles absolutely love them so I plant them to the side of my bok choy and turnips. This works out well, as we don't eat radish leaves and my family are not huge radish fans anyway. It's an easy sacrifice to make for us. Here are some more useful plants used to distract pests:
Dill and cilantro to trap aphids
Nasturtium to trap cabbage moths and aphids
Parsley to trap tomato pests
Radish to trap leaf miners, flea beetles and cucumber beetles.
Plants to attract pest predators
Think of your garden as a little ecosystem. Remember in school when you learned about food webs? A healthy garden is full of organisms that are both predator and prey to many other organisms. It happens on all scales: all the way from tiny microbes in the soil to hawks and coyotes keeping down bunny populations. It happens with our insect pests as well. If we provide food and shelter for predator insects (in the form of beneficial plants and a small population of pest prey) they will stick around and provide pest control for us when populations of pests get high. Note that this strategy involves restricting the use of pesticides in your garden. Pesticides not only kill the prey, they kill the predators. You also need to be tolerant of a small amount of pest damage. When you have absolutely zero pests, there will be no reason for predators to stick around. They will go elsewhere for food.
My absolute favourite example of predatory insects is parasitic wasps. This is where gardening can get fascinatingly gory, so skip this paragraph if you are squeamish. Parasitic wasps, such as the ichneumonid wasps, find a susceptible caterpillar, slice a small hole in their skin and lay their eggs inside the caterpillar. These eggs later hatch and the larvae eat the caterpillar from the inside out, saving the internal organs for last so that the caterpillar stays alive as long as possible. When the caterpillar finally dies, the larvae eat their way out and pupate, later to emerge as adults. Pretty gross, isn't it? I always did like horror movies. Take that cabbage fly caterpillars (insert evil mad scientist laugh)! Oh, and by the way, these guys don't sting people either. Their modified stinger is what they use to insert eggs into the caterpillar. Hoverflies act in a similar fashion, except they attach their eggs to the outside of caterpillars, beetles and bugs, they don't insert them inside the host.
Some predatory insects are just voracious killers. Everyone knows that ladybugs can eat hordes of aphids. Did you know that ladybug larvae eat even more aphids than the adults? Pirate bugs, tachinid flies, many beetles and spiders are also efficient pest killers. Helping these predators feel at home in our gardens will keep pest populations under control in the long term. Cutting back perennial plants in spring instead of fall will ensure these insects have a cozy place to overwinter in too. Here are some companion plants that are shelter and food for these predator insects:
Buckwheat, cosmos and fennel attract almost everything predatory
Alyssum attracts beetles and spiders (good for slugs) and parasitic wasps (good for caterpillars)
Anemone and penstemon attract minute pirate bugs (good for thrips)
Clover increases the number of predatory ground beetles (good for slugs)
Chrysanthemums attract tachinid flies (good for caterpillars and beetles) and attract parasitic wasps (good for caterpillars)
Dill attracts predatory wasps
Marigolds, parsley and chamomile attract hoverflies (good for aphids) and attract parasitic wasps (good for caterpillars)
Zinnias attract ladybugs (good for aphids)
Although companion planting can greatly help with pest control in our gardens, don't forget floating row covers, crop rotation and physical barriers such as fences. In addition, it is always helpful to plant varieties that are resistant to troublesome pests and diseases. A multi-dimensional approach is always the best strategy. And remember that healthy plants will be able to better fight off pests and diseases, so ensure you keep your soil healthy. Healthy soil equals healthy plants.
Plants to Improve Crop Flavour and Growth
Have you heard that if you plant basil with your tomato plants they will taste better? It's true! Not only that, your tomatoes will grow better too. This is a classic example, but there are other pairings out there that work equally well. Here are some examples:
Basil improves flavour and yield of tomatoes
Borage improves the flavour and growth of squash
Chamomile improves the flavour of onions
Nasturtiums improve the flavour and growth of cucumber
Summer savory improves the flavour of beans and onions
Thyme enhances the flavour of strawberries.
Other Types of Companion Plants
Physical support and protection
Cool season crops can be prone to bolting in hot weather so it pays to provide some shade for them in the hot summer months. We can make shade using tall crops and vining plants. For example, I train my cucumbers up a trellis that is tilted at a 45 degree angle and then I plant lettuces in the shade underneath it. Corn works equally well when planted on the south side of swiss chard or spinach. We can also use those taller crops as a type of trellis themselves for vining crops to climb up.
Inhibiting weeds
Empty spaces in the garden are prime real estate for weeds, so it pays to ensure every last square inch is planted. That's where ground covers come in. Alyssum and nasturtium and great examples of these. They can be planted in between larger specimens without shading them out. Any of the squashes and melons are also fantastic at sprawling over large areas to prevent weed growth.
Sweet alyssum (Lobularia maritima) is a multi-use companion plant. Yes, it is great at attracting pollinators, but it is also useful in pest control (it attracts predatory wasps) and is a great ground cover as well, crowding out weeds. Oh, and it also smells heavenly! Alyssum comes in a multitude of colours and is small enough that it can be planted easily in between most other plants. I personally like it between my lettuces and root vegetables. After cool season crops have bolted and are removed, alyssum is a great choice for a cover crop; just broadcast seed each area and wait for blooms. Then work the entire plant into the soil once the blooms are spent.
Improving soil
Did you know that peas and beans are not only great for eating, they also help improve the nutrition of your soil? Now you do! These plants are nitrogen fixers. They have nodes on their roots that work symbiotically with bacteria in the soil to pull nitrogen from the air and make it into a form available for plants to use. That nitrogen is released when the roots (or even the leaves and stems) remain in the soil to break down. Dynamic accumulators with deep roots often pull up micro-nutrients from deep down in the soil where other plants cannot reach them. When these plants break down they add those nutrients to the soil as well (see the article on food forests for more information on nutrient accumulators).
Cover crops work in this way too. They are planted either before the main crops or after they have been harvested before winter sets in. Once they have flowered, and before they have set seed, cover crops are turned into the soil so that they can break down and add their vast nutrition to the vegetable garden soil. Clover and buckwheat are two cover crops that work well in the Calgary area, even in smaller vegetable garden settings. Crops that improve your soil are great companions for all of your veggies!
The classic example of companion planting in this way is the three sisters. This is an intentional grouping of corn, squash and beans. The corn acts as a trellis for the beans to climb up; the beans are nitrogen fixers and add nutrients to the soil for the corn and squash; and the squash covers the soil, choking out weeds and defending against pests with its pokey stems and leaves.
Bad Companions
Before we finish talking about companion plants, we should really mention some really bad companions that we want to avoid planting together in our vegetable gardens. These are plants that either inhibit other plant's growth (usually via chemicals emitted from the roots), ones that attract or transmit specific diseases or plants that can interfere with seed collection by cross pollinating with each other. Here are plants you should never plant close together:
Fennel ≠ anything but dill (inhibits growth)
Cucumber ≠ herbs
Tomatoes ≠ kohlrabi (stunts growth), corn (attracts pests)
Peas and beans ≠ onion, garlic, gladiolas (stunts growth)
Pole beans ≠ beets (compete for growth)
Dill ≠ cilantro grown for seeds (they will cross pollinate)
Potato ≠ cucumber, tomato, raspberry (attract harmful potato pests)
Celery ≠ corn, asters (transmit aster yellows disease)
The time to think about companion planting is when you are planning out your vegetable garden in the winter or early spring. Consider the distances between companions. Repellent plants should be interspersed throughout, trap crops should be around the edges or to the side and pollinator plants and predatory insect plants just need to be kinda close. Also consider how multipurpose each companion plant can be. A plant that repels pests, chokes out weeds, improves the flavour of other plants, has beautiful flowers for cutting and that is also edible is a super efficient use of space (that's nasturtium by the way)!
Don't forget to get out there and observe your garden. Learn what pests are common for you and research what likes to eat them or what keeps them away. Record what you try each year and how effective (or not effective) it was. Remember to harvest and enjoy your veggies. Our vegetable gardens can beautiful and wonderfully diverse just like any other parts of our garden!
Yummy gardening everyone!
References and Further Reading
Veseys Seeds (https://www.veseys.com/ca/) for companion plant seeds.
West Coast Seeds (www.westcoastseeds.com) for companion plant seeds and also lists of companion plants for each crop (https://www.westcoastseeds.com/blogs/garden-wisdom/companion-planting)
T & T Seeds (https://ttseeds.com/) Longstanding Manitoba company with a huge variety of seeds as well as trees, shrubs, perennials and gardening accessories.
Mother Earth News Companion Planting Guide (https://www.motherearthnews.com/organic-gardening/companion-planting-guide-zmaz81mjzraw)