Companion planting is based on long time observations of the benefits of growing certain types of plants near each other. For example, the Native American Iroquois planted beans, corn and squash together, a combination known as ”The Three Sisters”. The corn provides a support for the beans to climb up, the beans provides nutrients (nitrogen) for the soil and the squash shades the roots of the other plants helping to retain moisture and keep the weeds down.
Organic gardeners encourage companion planting because the practice supports the control of pests and diseases without using chemicals.
Here are some of the known benefits of companion planting:
- Protection from disease – Planting compatible plants close together avoids creating a monoculture. If a disease strikes one plant, the companion plant serves as a protective barrier thus deterring the spread of disease to other plants.
- Deter pests – Certain plants secrete chemicals that deter pests. For example, the scent of marigolds repels aphids.
- Trap cropping – Certain plants attract pests away from other plants. For example, nasturtiums attract caterpillars from plants they could harm, such as lettuce.
- Attract pollinators – Some plants such as fruit bearing trees and vines require cross pollination by bees and insects. Flowering plants growing nearby attract these pollinators.
- Save space – Plants that benefit each other can be closely planted because they do not compete for nutrients, sun or water. For example, plant radishes with carrots because radishes are picked first, leaving room for the carrots to fill in.
- More flavourful vegetables and fruits – Some companion plants are thought to improve the flavour of other vegetables and fruits growing nearby, for example tomatoes and basil.
- Improving the soil – Some plants, such as peas and beans, fix nitrogen in the soil making it available to the surrounding companion plants.
Compatible Plant Combos
Finding out which plants make good companions in your garden can involve experimentation. While over time combinations such as the ones we list below have proved beneficial for many gardeners, much depends on the conditions in your garden.
- Coriander, sage and rosemary planted near carrots repel the carrot rust fly.
- Tarragon and marjoram give off a scent that repels most insects.
- Sage, rosemary and thyme repel insects that feed on brassicas (plants in the cabbage family).
- Asparagus repels nematodes that attack tomatoes and tomatoes repel asparagus beetles
- Alyssum attracts pollinating insects and is a useful mulch to keep weeds down between veggie rows.
- Basil improves the flavour and vigour of tomatoes and repels flies, mosquitoes, and thrips.
- Chives improve the flavour of carrots and tomatoes, and repel aphids, carrot rust fly and Japanese beetles.
- Borage deters tomato hornworm and cabbage worms.
- Calendula repels a number of bad nematodes in the soil. Plant with tomatoes and asparagus.
- Catnip attracts pollinators (and cats), but repels aphids, flea beetles, Japanese beetles, ants, weevils, and squash bugs.
- Dill attracts predatory wasps that feed on garden caterpillars, and it repels aphids and spider mites.
- Garlic planted near roses helps to repel aphids.
- French Marigolds produce a chemical that kills nematodes and repels whiteflies.
- Nasturtiums are a good trap for aphids and they deter whiteflies and cucumber beetles.
- Spinach, lettuce, and arugula are "good neighbor" crops for tomatoes. They stay small and grow better in hot weather when shaded by the tomato plants.
Plants That Aren’t Compatible
While some plants are beneficial to one another, others may hinder one another. For example, fennel and kohlrabi inhibits the growth of tomatoes. And, planting tomatoes and potatoes together is not recommended, since both are susceptible to the mosaic virus which spreads from one crop to another.