Companion planting is the practice of putting different plants together in the garden to benefit one or both of them. It can be as simple or as complicated as you want to make it. Some of the charts listing plants that should be together are so complicated that they scare people.
The idea is that some plants repel pests, attract beneficial insects, or alter the soil in some ways. Some plants just don’t like to grow next to each other. Growing different plants in the same space can maximize the available space. It can also limit pest damage to your crop if your crop is spaced out throughout the garden. You have less chance of all your crop being destroyed. Sometimes one plant can protect another from harsh weather. Some crops like cooler, shadier growing conditions, so they can be planted at the base of something taller. Sometimes planting a sacrificial crop that is particularly tasty to a nasty pest, can keep that pest away from your plants.
The Three Sisters is a popular example of a system intended to benefit all three plants. The system is commonly attributed to Indigenous agricultural practices being developed before contact. Corn is planted with pole beans and squash, the idea being that the corn provides support for the climbing beans. Beans also fix nitrogen in the soil. The squash plants provide ground cover, protecting the roots from moisture loss, and sun, while also keeping weeds at bay. The squash are said to keep raccoons away from the corn and beans, because the raccoons do not like the prickly squash vines on their feet. In my experience, it takes a lot more than a few prickly squash plants to deter raccoons, but the rest of the plan is sound.
The first companion plant that most people discover is the marigold. There are many different kinds, colours, and sizes. Marigolds attract bees, pollinators, and other beneficial insects such as ladybugs, parasitic wasps, and hoverflies. These beneficial insects attack nasties, such as aphids. Parasitic wasps destroy tomato hornworms by laying their eggs in the body of the hornworm. Marigolds can be a trap crop for some things, such as slugs, and can repel some insects such as squash bugs.
Some plants, although very beneficial in many ways, just don’t do well with other things. Fennel is a good example. It will stunt the growth of some things planted near it, such as bush beans or tomatoes. But, it is a food for the swallowtail butterfly, and it attracts hoverflies, ladybugs, parasitic wasps, and tachnid flies. Those are all beneficial insects, so plant lots of fennel on the edge of your garden, just not right beside your vegetables! Basil goes hand and hand with tomatoes. It improves their flavour, and helps repel tomato hornworm. All beans fix nitrogen in the soil, so plant them with carrots, cucumbers, peas, brassicas, and eggplant. Pole beans and beets stunt each other. Borage is excellent for attracting pollinators, so plant it next to squash or cucumbers, and it repels tomato hornworm and cabbage moths. Catnip attracts pollinators and parasitic wasps. It also repels aphids and squash bugs. Oregano and Marjoram repels cabbage moths. Radishes grow fast, and are good companions for beans, beets, cucumbers, peas, and tomatoes. Try planting a few radishes around where you are going to plant squash. Let them grow and bloom. Most of the herbs provide some protection in your garden and attract beneficial insects. Most flowers will also attract beneficial insects and pollinators.
Biodiversity is always a goal in our gardens. Learning what plants can be planted together to maximize your space and yield is just another way to appreciate the diversity, and to use each of the plants to its potential. Even if companion planting seems daunting, and honestly, it does to most gardeners I think, just shake things up a bit. Stick some herbs or flowers between groups of vegetables. Don’t be afraid of interspersing one thing with another.