Companion Planting in the Vegetable Garden | UC Agriculture and Natural Resources

February 3rd, 2025

Companion planting and intercropping are two planting methods that include growing a variety of plants in close proximity. When we grow different types of vegetables, herbs, and flowers together, they can work together to create a healthier and more productive garden. A reduced reliance on pesticides and fertilizers is also possible when following these planting methods.

Monoculture vs Polyculture. Monoculture is an agricultural term describing when a single species of plant is grown in the same place for an extended period. This term describes the kind of planting done by many industrial food producers. This lack of biodiversity can raise the risk of insect and disease outbreaks and reduce soil fertility. Polyculture is when we choose different plants to grow together. This mimics the way plants grow in natural systems and creates biodiversity. Biodiversity is important because it can create a more stable environment for plants to thrive.

Inter-cropping. This method involves planting a variety of crops that grow or mature at different rates to increase production in a small area. Radishes or leaf lettuce planted between or alongside pepper, eggplant, tomato, or corn plants is a good example. The radishes and lettuce can be harvested before the other plants reach their full mature size. Also, since lettuce and radishes tend to prefer cooler conditions and require less direct sunlight, they can also be left to grow in the shade of the taller plants when the weather heats up later in the season. When inter-cropping, it is important to consider the cultural needs of each plant. They should have similar water, temperature, soil, and nutrient needs.

Photo of interplanting of shallots and lettuce — Interplanting of winter and spring-grown shallots and lettuce

Companion planting. This appears at first glance to be the same as inter-cropping. But in addition to maximizing your space, planting certain types of plants together can help deter harmful insects, attract beneficial insects, and increase soil fertility. An example of this is the ‘Three Sisters' planting method used by Native American tribes for hundreds of years. It involves planting corn, pole beans, and squash together. The tall corn plants provide a structure for the pole beans to grow on while the beans enrich the soil by fixing nitrogen from the atmosphere. The squash plants shade and cool the soil surface, reducing evaporation. Many common vegetable plants can be good companions for others.

Repelling pests. Some research findings have supported the idea that companion planting can result in some degree of pest deterrent. But there is also conflicting information to be found. Some ideas about companion planting have been passed down from gardener to gardener through the generations, and some have been studied, tested, and proven. However, many claims lack scientific proof they are effective. So be aware that a particular companion planting strategy may or may not be effective in your garden.

In some cases, planting bright colored, strongly scented, or nectar producing flowers may distract or confuse insects as they make their way to your plants. Although insects may not have a high degree of intelligence, they have been around a very, very long time, and they are very adept at finding the plants that they need to survive. Anyone who has planted marigolds next to their cabbage or broccoli plants will attest to the fact that the cabbage butterflies seem to have no trouble finding and depositing their eggs on your crops. While this may be the case, studies have shown that by combining these two plants, a reduction in pest activity can often be seen.

A healthy garden bed combining a variety of flowers and vegetables

Attracting beneficial insects. In addition to repelling some pests, growing herbs and flowers in your vegetable garden can help lower pest populations in another way. Providing nectar and pollen sources can increase populations of beneficial insects. Some beneficial insects such as bees and butterflies are important pollinators in our gardens. Other beneficial insects such as lady beetles, syrphid (hover) flies, and green lacewings are predatory and feed on garden pests. Many predatory insects use the pollen as an alternate food supply when insect pests are less available. There are many varieties of flowering plants that can be effective at attracting beneficial insects to the garden. Some examples of these are: alyssum, marigold, calendula, cosmos, zinnia, sunflower, borage, and phacelia.

Allowing some of your vegetable or herb plants to mature and set flowers is another way to attract these same beneficial insects. Some great choices for this are dill, basil, cilantro, parsley, broccoli, chives, arugula, thyme, and oregano. Not only do they do a good job of attracting the kind of insects you want in your garden, they are also a beautiful addition to the garden. It is important to remember that in addition to attracting these beneficial insects, we need to keep our gardens a safe environment for them to flourish. That means decreasing or eliminating the use of pesticides whenever possible.

Phot of spring flowers and vegetables happily coexisting in the garden — Spring flowers and vegetables happily coexisting in the garden

Boosting soil fertility. There are several legume plants that can be grown in the vegetable garden to increase fertility. Beans, peas, and clovers are all legumes. They have a symbiotic relationship with bacteria in their roots and can convert nitrogen from the air into a form that other plants can use. Along with potassium and phosphorus, nitrogen is among the top 3 important nutrients for plant development. While there are several legumes that are commonly grown in the winter months as a cover crop, mixing them between rows of winter crops or growing warm season legumes alongside your summer vegetables can also reduce the need to use nitrogen fertilizers.

Photo of Purple cauliflower and fava beans — Purple cauliflower and fava beans

Allelopathy and bad companions. Be aware that some plants can harm others if grown nearby. Allelopathy is the ability of some plants to produce compounds that kill or inhibit the growth of other plants. Most of these plants are not usually found in the vegetable garden, such as black walnut. But there are a few that you may grow in your garden that might surprise you. They are sunflowers and fennel. If you grow these plants, keep them separated from your vegetables, in a separate bed, or in an area several feet from other plants. There are also some bad companions these are vegetable plants that are best kept apart because they attract the same pests or compete for nutrients. Avoid planting tomatoes and brassicas (cabbage, broccoli, and cauliflower) or tomatoes and corn together. All are heavy feeders (they need a good supply of nutrients in the soil) and will compete for the same nutrients. Cucumbers and melons are in the same family, and so are carrots and dill. They will attract the same pests.

Photo of sunflowers — Sunflowers are great at attracting pollinators, but they are not the best choice as a companion plant

While not all claims made about companion planting can be proven scientifically, we can use companion planting methods along with those of polyculture and inter-planting to create healthier soil and more productive, biodiverse gardens. By doing so we not only provide habitat for pollinators and beneficial insects, but for other beneficial creatures that also help to control pest populations such as birds, lizards, and frogs. A garden full of life is a healthy garden.