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These plants are true companions

May 28, 2011

BECOMING A SUCCESSFUL organic gardener requires promoting vigorous plant health using a variety of methods, including alternatives to synthetic pesticides. These methods include composting, mulching, proper watering, proper plant selection and companion planting. Groups of plants that grow well together are called companions. Companion planting is a method of placing different plants together to aid in their healthy growth.

Companion planting has a long agricultural history. Many of the modern principles were being utilized in English cottage gardens and home gardens in Asia many centuries ago. Before the arrival of Europeans, Native  Americans practiced a system of planting the "three sisters" of corn, beans and squash together to provide a symbiotic relationship. The corn offers a support for the climbing beans, which in turn help replenish the soil with nutrients. The large leaves of the squash provide living mulch that conserves water and helps to provide weed control.

The actual mechanisms of beneficial plant interaction have not always been well understood or supported in the scientific community. Interest is growing in using the special properties of individual plants to our advantage when we grow our foods and ornamentals, on the theory that they support each other in nutrient uptake, pest control, pollination,
shade protection and any other factor necessary to increase productivity. For most gardeners, the combinations of plants make for a more varied, visually attractive garden that allows for more productive use of our often small spaces.

Companion plants can help each other in a variety of ways:

•Security through diversity: In a monoculture, where many of the same type of plants are planted together, pests can easily spread from one plant to the next. Mixing with companion plants can interrupt this cycle of spread.

•Beneficial habitats: The benefits are realized when companion plants provide a desirable environment for beneficial insects and other arthropods such as predatory (think ladybird beetles) and parasitic (think wasps) species. This can help keep pest populations under control. Companion plants can repel pest insects, weeds, nematodes or pathogenic fungi
through chemical means. Sometimes, a companion plant can be more attractive to pests and may keep them from infesting the main crop. Plants that produce copious nectar or pollen can attract larger quantities of beneficial insects that control pests and increase yield. It is important to avoid planting together plants that are susceptible to the same insect species or diseases.

•Nitrogen fixation: Legumes such as peas and beans have the ability to fix atmospheric nitrogen for their own use and to help neighboring plants through a symbiotic relationship with Rhizobium bacteria.

•Mutual protection: Tall sun-loving or densely foliaged plants can provide shade, higher humidity or a wind break for lower-growing, shade-tolerant plants. This allows more plants to be planted in a smaller space, thereby increasing yield in your space.

•Self-protection: Some plants repel other plants as a way to avoid competition. They inhibit seed germination and can serve as natural weed barriers.

Remember that vegetables, herbs and flowers can work well together, both as cooperative companion plants and as visually pleasing aspects to your garden. It is possible that planting flowers near the vegetable garden will attract beneficial insects. Let's look at some of our most common garden vegetables, flowers and herbs and see what we can plant together or what is best kept away from each other.

Tomatoes grow well with basil, parsley, carrots, chives, onion, parsley, marigolds and nasturtium. Potatoes and tomatoes can be attacked by the same blights, so they should not be planted together.

Lettuce grows well with strawberries, cucumbers, carrots and, especially, radishes. Tall pole beans can partially shade lettuce, which needs cool weather and ample moisture and, in that way, can extend our lettuce planting season.

Corn can help pole beans by acting as a trellis and peas and beans help corn by returning the nitrogen to the soil used up by the corn. Sweet corn does well with potatoes, cucumbers, squash and pumpkins.  It is best not to plant tomatoes with corn because the tomato fruitworm and corn earworm are the same.

Carrots are good with tomatoes, lettuce, chives, onions, leeks, rosemary, sage and radishes. Letting some of your carrots produce flowers can  attract some predatory wasps, assassin bugs and lacewings.

Chile pepper plants need direct sun, but their fruit can be burned by it. Pepper plants grown together or with tomatoes can shelter the fruit from intense sunlight and raise the humidity level for the plant.

Radishes make excellent trap crops by attracting cucumber beetles among squash and cucumbers.

Basil planted among tomatoes may repel tomato hornworms.

Chives can be planted at the base of roses to repel aphids.

Dill is a good friend to cabbage and does well with corn, lettuce, onions and cucumbers. It attracts honeybees and other beneficial insects while repelling aphids, spider mites, squash bugs and cabbage looper.

Marigolds are helpful in both flower and vegetable gardens. The roots of some French and African marigolds contain a substance that is toxic to certain types of nematodes, soil-inhabiting microscopic roundworms that damage many species of plants.

Scientists have not spent much time looking at the relationships among plants but testimonials shared by many observers often turn out to be true. Keep track of where you plant and observe what happens. Maybe you will find a new combination of plants that make good companions.

Companion planting is easy, practical and fun. There are many good sources with more information for you to explore. Louise Riotte has written two easy-to-use books with lots of practical gardening advice that will support your efforts at companion planting. They are "Roses Love Garlic" and "Carrots Love Tomatoes." The Cornell University gardening website provides excellent, science-based information: www.gardening.cornell.edu/factsheets/ecogardening/complant.html.

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