Companion Planting: Which Vegetables Grow Well Together

Companion planting is the practice of growing different plants in close proximity for mutual benefit. The benefits are real but more nuanced than the folklore around the subject sometimes suggests: some combinations do measurably reduce pest pressure or improve yields, while others are based more on tradition than evidence. This guide focuses on the companion relationships with the strongest practical support.

How Companion Planting Works

Several distinct mechanisms explain why some plant combinations work better than others growing in isolation.

Pest confusion and masking: Strong-scented plants like basil, marigolds, and alliums interfere with the ability of flying pests to locate their target crops by smell. Interplanting carrots with onions, for example, is thought to reduce carrot fly and onion fly pressure because the mixed scents make it harder for each pest to locate its preferred host.

Pest trap cropping: Some plants attract pest insects away from the main crop. Nasturtiums planted at the edge of a brassica bed draw aphids to themselves, keeping aphid populations concentrated where they can be managed or removed without affecting the crop.

Beneficial insect habitat: Flowering plants interplanted in vegetable beds attract predatory and parasitic insects that control pest populations. Dill, fennel, and phacelia are particularly effective at supporting hoverflies, lacewings, and parasitic wasps.

Nitrogen fixation: Legumes including peas, beans, and clover fix atmospheric nitrogen through root nodule bacteria, enriching the soil for neighboring plants that need more nitrogen.

Physical support and shade: Tall crops provide shade that protects low-growing shade-tolerant crops from intense summer sun. Climbing beans grown up corn stalks is the classic example from the Three Sisters system.

Proven Companion Combinations

The Three Sisters (corn, beans, squash): This Native American planting system pairs tall corn that provides a climbing support for beans, nitrogen-fixing beans that enrich the soil, and large-leafed squash that shades the ground to suppress weeds and retain moisture. The combination works well as long as spacing is adequate for each crop.

Tomatoes and basil: Widely practiced and consistently reported to produce healthier tomatoes. Basil is thought to repel thrips and possibly aphids, and the companion combination improves air circulation around the base of tomato plants compared to dense mono-plantings.

Carrots and onions: Interplanting these two crops in alternating rows or mixed patches is a traditional method for reducing carrot fly and onion fly pressure, with some experimental support.

Brassicas and nasturtiums: Nasturtiums act as aphid trap crops, drawing blackfly and greenfly away from kale, cabbage, and broccoli. Check nasturtiums regularly and remove heavily infested parts to prevent the aphid population from overwhelming the trap plant and spilling back to the crop.

Beans and brassicas: Beans fix nitrogen that brassicas use heavily. Planting beans in the same bed as brassicas, or preceding brassicas in a rotation after a bean crop, improves brassica yields in lower-fertility soils.

What to Keep Apart

Some plant combinations are allelopathic: one plant releases compounds that inhibit the growth of another. Fennel is the most significant example in the vegetable garden, inhibiting the growth of tomatoes, peppers, beans, and many other crops. Grow fennel in isolation rather than in mixed vegetable beds.

Onions and garlic grown near beans and peas are sometimes reported to reduce legume yield, though the evidence is less consistent than for fennel’s effects. Keeping alliums and legumes in separate sections of the crop rotation plan avoids any potential competition.