Companion Planting Chart and Guide for Vegetable Gardens

Companion Planting Chart for Vegetables

A companion planting guide answers two questions: which plants help a vegetable when they grow nearby, and which ones to keep apart. The chart below covers 10 common crops. Each pairing comes from a university extension source, and the reason sits in the third column so you can judge whether it applies to your bed. The short version is that scented herbs go beside tomatoes and brassicas, flowers go on the border, tall crops go on the north side, and beans stay away from onions.

Crop	Plant nearby	Why it helps	Keep apart from
Tomatoes	Basil, parsley, early peas at the base of the cage	Scented herbs make hosts harder for aphids to find; peas use the cage before tomatoes fill it	Corn, potatoes, fennel, cabbage family
Peppers and eggplant	Basil, parsley, beans, marigolds	Same scent effect as with tomatoes	None listed
Broccoli, cabbage, kale	Thyme, onions, nasturtium	Reduced caterpillar damage in broccoli	Dill, strawberries, pole beans, tomatoes
Beans	Corn, carrots, lettuce, most herbs	Pole beans climb corn; the nitrogen they fix is released after the plants break down	Onions, garlic
Corn	Pole beans, squash, pumpkins, peas, cucumbers	The three sisters arrangement	Tomatoes
Cucumbers	Nasturtium, marigolds, radishes, beans, corn	Less damage from cucumber beetles	Potatoes, aromatic herbs
Squash and pumpkins	Nasturtium, marigolds, corn, a Blue Hubbard trap crop	Less squash bug damage; trap crop draws bugs and borers	Potatoes
Lettuce and salad greens	Carrots, radishes, cucumbers, sweet alyssum border	Alyssum feeds aphid predators; grows in the shade of taller crops	None listed
Potatoes	Beans, corn, cabbage family, marigolds, horseradish	Listed as compatible neighbors	Tomatoes, squash, pumpkins, cucumbers, sunflowers
Carrots	Lettuce, peas	Listed as compatible neighbors	Dill

The “keep apart” column follows the companion chart prepared for the University of California Master Gardener program. Charts like this record long-standing garden observation, so treat a “keep apart” entry as a reason to put the two crops in different beds when you have the room.

How to Use the Chart

Read the “why” column before you copy a pairing. Companion planting works through a handful of mechanisms, and each one has a condition attached. Scent masking needs the herb close to the crop. A border of flowers needs to be in bloom when aphids arrive. A trap crop needs a head start of about 2 weeks. If the condition is missing, the pairing does nothing except take up space.

University of Illinois Extension is blunt about the limits: little research on companion planting has been done at garden scale, and many recommendations rest on anecdotal evidence. Treat the chart as a way to arrange crops you already planned to grow. A bed with several plant families and little bare ground makes it harder for plant-eating insects to find their hosts, and that general effect is better supported than most single pairings.

Pairings With Evidence Behind Them

Scented herbs beside vegetables. University of Maryland Extension reports that the volatile compounds of alliums, basil, rosemary, lavender, dill, cilantro and chives repel aphids and other insects or make it harder for them to locate host plants. That is the case for basil next to tomatoes, peppers and eggplant. The same source notes that thyme, onion and nasturtium help reduce caterpillar damage in broccoli, and that slugs avoid mint, rosemary and thyme. For more on the herb side of these pairings, see herbs that repel garden pests.

Flowers for beneficial insects. Many predators and parasitoids need pollen and nectar as adults. Sweet alyssum is the usual choice for a border because it stays 3 to 9 inches tall and can be set out as a row between crops. Iowa State University Extension notes that it draws lady beetles and hoverflies, and that an adult lady beetle can eat as many as 50 aphids per day. Alyssum seed germinates in 7 to 20 days and needs light, so scatter it on the surface and leave it uncovered.

A trap crop for squash pests. Blue Hubbard squash is highly attractive to squash bugs, squash vine borers and cucumber beetles. The University of Missouri’s pest management program advises 6 to 8 Blue Hubbard plants for a garden of about 100 cucurbits. Set out 2-week-old transplants when you sow the main crop, or at least 2 weeks before you transplant it, and place them at the corners 3 to 8 feet from the main planting. The pests that gather on the trap plants then have to be killed there, or the trap becomes a nursery. Both pests are covered in squash bugs vs. squash vine borers and squash vine borer prevention.

Marigolds, with a caveat. Some French and African marigolds carry a chemical in their roots that suppresses root-knot nematodes. Penn State Extension describes the method that works: sow a thick cover crop of marigolds in spring, grow it for several months, then till or dig the plants in. The same publication states that interplanting marigolds among vegetables does not affect root-knot nematode populations. Maryland lists marigolds and nasturtiums as helping reduce damage from squash bugs and cucumber beetles, which is a separate and more modest effect.

Height and shade. Plant low, shade-tolerant salad greens on the north side of corn, tomatoes or eggplant, where the taller crop shields them from summer sun. In early spring, sow peas at the base of tomato cages on the north side. The peas climb the cage and finish before the tomatoes need the room.

Three Sisters: The Oldest Companion Planting Guide

Corn, pole beans and squash grown together is the best-known companion planting system in North America. Corn supports the beans. Beans fix nitrogen, though Cornell notes that most of it is not available to the corn and pumpkins in the first year, because the bean roots have to break down to release it. Squash sprawls across the ground like a mulch, suppressing weeds and holding moisture, and its spiny stems discourage animals from feeding on the other two.

Cornell’s garden-based learning program gives planting numbers. Prepare low hills 3 to 4 feet apart within and between rows. Once the ground is warm, which Cornell puts at late May, place 5 to 7 corn seeds in each hill at a depth of 1 to 1 1/2 inches. When the corn is about 6 inches high, plant 4 or 5 pole bean seeds in each hill and 4 or 5 pumpkin seeds in every seventh hill. The planting needs an inch of water per week from rain or irrigation.

Two cautions keep expectations realistic. Cornell warns that interplanting without added fertilizer may lower yields, since all three crops feed from the same hill. Illinois Extension adds that there is no compelling published evidence the system improves productivity or soil quality over growing the crops separately. Grow it for the space it saves and for its history, and fertilize the hills as you would a corn row.

Plants to Keep Apart

The best-documented conflict on the chart is onions with beans. A University of Wisconsin Extension list states plainly that garlic, onion and shallot stunt the growth of beans, and that onions stunt peas as well. Keep the allium row in a different bed from bush beans, pole beans and peas.

Tomatoes and potatoes are another pair to separate. The Wisconsin list notes that the two are attacked by the same blight, and the University of California chart marks them as incompatible. The same chart keeps fennel away from tomatoes, dill away from carrots and the cabbage family, and potatoes away from squash, pumpkins, cucumbers and sunflowers. Fennel is easiest to manage in its own container or at the far end of the garden.

Shade is the conflict charts tend to leave out. A row of staked tomatoes or corn on the south side of a bed will shade whatever grows behind it for much of the day. That suits shade-tolerant salad greens and works against sun-loving crops such as peppers. Put the tallest crops on the north edge unless shade is the goal.

Laying Out a Bed With Companions

Start with the crops you want to eat, then add companions in three passes. First place the tall crops on the north side and the shade-tolerant greens behind them. Next tuck scented herbs between the vegetable plants along the row: basil with tomatoes and peppers, thyme or onions with broccoli and cabbage. Last, edge the bed with sweet alyssum and put any trap crop at the corners.

Give every companion its own root space. A basil plant jammed against a tomato stem competes for the same water, and no pest benefit makes up for a thirsty tomato in August. Follow the spacing on the seed packet for each plant, and count the companion as a plant when you work out how many fit. If you are still choosing a bed, the dimensions in raised garden beds for vegetables show how many rows each size allows.

Companion planting lowers pest pressure without removing it, so keep scouting. Check the undersides of squash leaves for egg clusters weekly, handpick caterpillars on brassicas, and rotate plant families to a new spot each year so soil pests such as root-knot nematodes do not build up under the same crop.

Quick recap

• Use the 10-crop chart to place neighbors, and read the reason column before copying a pairing.
• Basil, thyme, onions and other scented plants go in the same row or bed as the crop they protect.
• Sweet alyssum on the border feeds lady beetles and hoverflies that eat aphids.
• Blue Hubbard squash works as a trap crop when planted 2 weeks ahead and 3 to 8 feet away.
• Marigolds suppress root-knot nematodes only as a dug-in cover crop grown for several months.
• Keep beans away from onions and garlic, and tomatoes away from corn, potatoes and fennel.