Companion Planting for Vegetable Gardens

Companion planting means growing more than one species close together for a useful reason. Radishes and carrots are a simple example. The radishes mark a slow carrot row and are pulled before the carrots need the space. Leaf lettuce can use light shade beside a taller crop when it still receives enough air and water.

An herb belongs on an edge if you want to cut it often. Do not add another plant simply because a chart recommends the pairing. Ask what it will do after the main crop reaches full size. If it will be crowded or out of reach, the pairing is not earning its space.

Put the largest crop or support in place first. Leave its harvest side open. Use the remaining edge for a smaller crop only when both plants will have enough light and root space. A small bed can hold a mixed planting, but access is part of the design.

Do not count on root depth alone to prevent competition. A living mulch such as white clover can suppress weeds, but it can also compete with annual vegetables for water and nutrients. It is better suited to a carefully managed trial than to an automatic underplanting beneath tomatoes.

Sweet alyssum makes a low flowering edge that can feed adult hoverflies. Their larvae hunt aphids on nearby crops. In lettuce trials, alyssum plantings have been associated with lower aphid pressure, but they do not replace inspection. In a brassica bed, watch alyssum too. It can host flea beetles in some regions.

Let a few dill or cilantro plants bloom at an outer edge. Their flat clusters of small flowers are easy for small parasitic wasps and flies to use. Keep the flowers where you can reach the vegetables beside them. Plant an insectary border to support predators, not as an invisible shield against pests.

Marigolds do not create a pest barrier around tomatoes. Their reputation comes from research on certain French marigolds used as a dense, pre-plant cover crop for some root-knot nematodes. A single marigold tucked beside a susceptible vegetable will not protect it.

This is a crop-rotation treatment, not ordinary companion planting. The response depends on the marigold cultivar and the nematode species in the soil. In warm conditions, the cover crop needs a full growing period before the next susceptible vegetable. Do not expect chopped marigold residue to do the same job as living roots.

The Three Sisters tradition has many regional forms, but its sequence matters. Sow corn first. After the corn has emerged and begun to stand on its own, plant pole beans around it. Set squash at the outer edge or between mounds where the vine has room to run without covering the working path.

That arrangement needs more room than many four-by-eight beds offer. If the squash will cover the access side or the corn will shade the rest of the planting, choose one tall crop with a simple edge planting instead.

A pairing earns a repeat when the smaller crop finishes before the larger one closes in and harvest stays easy. If flowers are in the way, move them to the edge next season. If one plant shaded another, give the larger crop more room.

Basil can be handy beside tomatoes when both have space, but it will not change tomato flavor. Carrots and tomatoes can share a bed, but neither crop needs the other to grow. Companion planting should make ordinary garden work simpler, not give you another system to maintain.

• Flea beetles on brassicas and eggplants
• Trap crops for pest management
• Crop rotation guide
• How PlotSmarter plans a garden