Companion planting is based on the concept that the qualities of some plants can benefit others when planted nearby.
Some plants repel pests and help others by keeping the pests away from them and then for example other plants will help to enrich the flavour of other plants. This list covers some of the big partnerships but there are many, many more possible combinations.
Agastache: Attracts bees. Maintain one row slightly away from the garden to lure cabbage moths away from Brassica crops. Do not plant Agastache near radishes.
Alyssum: Attracts pollinators. Good as a mulch to keep weeds down between rows.
Amaranth: Attracts predatory ground beetles. Plant along side corn to shade the soil and helps to retain water.
Asparagus: Plant with asters, basil, cilantro, dill, cilantro, marigolds, nasturtiums, oregano, parsley, peppers, sage, and thyme. Asparagus repels nematodes that attack tomatoes, and tomatoes repel asparagus beetles.
Basil: Improves vigor and flavour of tomatoes if planted side-by-side. Also good with asparagus, oregano, and helpful to peppers. Basil helps repel flies, mosquitoes, and thrips.
Broad beans: Excellent for fixing nitrogen in the soil. Don’t plant near onions.
Beans – Bush & Pole : All beans fix nitrogen in the soil. Plant with beets, carrots, celery, chard, corn, cucumber, eggplant, peas, potatoes, radish, and strawberries. Not recommended to plant near chives, garlic, leeks or onions. Pole beans and beets stunt each other’s growth, ensure distance between these.
Beans – Soya: Good for fixing nitrogen, and acting as a mulch against weeds. Grow with corn. Soya beans repel Japanese beetles and chinch bugs.
Beets: Add minerals to the soil. The greens are very good for the compost. Plant with bush beans, Brassicas, corn, garlic, kohlrabi, leeks, lettuce, and mint. Add cut mint leaves as a mulch for beets. Avoid planting beets near pole beans.
Borage: Excellent all around companion plant. Borage deters tomato horn worm and cabbage worms, and is particularly good planted near tomatoes and strawberries. Very attractive to pollinators, and excellent for the soil and compost. Borage is deer resistant.
Brassicas: Encompassing many vegetables such as broccoli, brussel sprouts, cabbage, carrots, cauliflower, celery, chervil, chives, collards, cucumber, kale, turnip. All benefit from chamomile, dill, mint, rosemary, and sage. Avoid planting near eggplants, peppers, potatoes, or tomatoes.
Buckwheat: Fixes calcium in the soil, and makes an exceptionally good green manure plant. Buckwheat absorbs nutrients that are not available to other plants, and can then be composted or tilled under, releasing those nutrients in accessible forms.
Calendula: Repels a number of bad nematodes in the soil, but may attract slugs. Plant with tomatoes and asparagus.
Carrots: Plant with beans, Brassicas, chives, leeks, lettuce, onions, peas, peppers, pole beans, radish, rosemary, sage, and tomatoes. Avoid planting with dill, parsnips, and potatoes.
Carrots planted near tomatoes may have stunted roots, but will have exceptional flavour. Chives also benefit carrots.
Catnip: Attracts pollinators-and cats, but repels aphids, flea beetles, Japanese beetles, ants, weevils, and squash bugs.
Celery: Good partner for beans, Brassicas, cucumber, garlic, leek, lettuce, onion, and tomatoes.
Chamomile: Attracts hover flies and wasps. Plant near onions to improve their flavour.
Chervil: Excellent companion for Brassicas, lettuce, and radishes. Chervil helps to repel slugs.
Chives: Improves the flavour of carrots and tomatoes. A companion plant for Brassicas. Helps to repel aphids, carrot rust fly, and Japanese beetles. Avoid planting near beans and peas.
Chrysanthemum: White flowering mums repel Japanese beetles.
Cilantro: Repels aphids, potato beetles, and spider mites. Plant near cilantro.
Clover: Attracts many beneficial insects and helps build the soil. Helps fight cabbage worms, and increases the number of predatory ground beetles.
Collards: Plant near tomatoes, repels flea beetles.
Corn: Companion to beans, beets, cucumber, dill, melons, parsley, peas, potato, soya beans, squash, and sunflower. Avoid planting next to celery or tomatoes. Amaranth makes a great mulch between rows by competing with weeds and conserving ground moisture.
Cucumber: Plant beside asparagus, beans, Brassicas, celery, corn, dill, kohlrabi, lettuce, onion, peas, radish, and tomatoes. Avoid planting near potatoes and sage. Dill helps cucumbers by attracting predatory insects, and nasturtiums will improve the flavour and growth of cucumbers.
Dill: Improves the health of cabbages and other Brassicas, a very good companion for corn, cucumbers, lettuce, and onions. Dill attracts the predatory wasps that feed on garden caterpillars, and repels aphids and spider mites. Avoid planting near carrots and tomatoes.
Eggplant: A good companion for amaranth, beans, marigolds, peas, peppers, spinach, and thyme. Do not plant eggplants near fennel.
Fennel: Not a companion for any garden food plant. Fennel will inhibit growth of bush beans, kohlrabi, tomatoes. If you must have it plant it outside of the veggie garden.
Flowers: Attractive to pollinators as well as beneficial predatory insects: hover flies, pirate bugs, tachinid flies, and lady beetles.
Garlic: Planting garlic near roses will help to repel aphids. Because of its sulphur compounds, it may also help repel white flies, Japanese beetles, root maggots, carrot rust fly, and other pests.
Kohlrabi: A worthy companion for beets, Brassicas, cucumbers, and onions. Avoid planting near peppers, pole beans, strawberries, and tomatoes.
Leeks: Grow with beets, carrot, celery, onions, and spinach. Avoid planting near beans and peas. Leeks help repel carrot rust flies.
Lettuce: Good companions for beets, Brassicas, carrot, celery, chervil, cucumbers, dill, garlic, onions, radish, spinach, squash, and strawberries.
Marigold: French Marigolds produce chemicals that kill nematodes and repel whitefly. Avoid planting them near beans. Mexican Marigolds have the same effect, and may repel rabbits.
Melon: Great companions for corn, marigolds, nasturtiums, pumpkin, radish, squash, and sunflowers. Avoid planting near potatoes. Melon leaves are full of calcium, so they’re good for the compost heap.
Mint: Attracts earthworms, hover flies and predatory wasps, and repels cabbage moths, aphids, and flea beetles. Mint is very invasive, keep it in containers around the vegetable garden and it’ll never take over. Avoid planting near parsley.
Nasturtium: Great sacrificial crop as they attract aphids away from anything else that you are growing. They deter white flies, cucumber beetles, and attract predatory insects. It is a good companion for Brassicas, cucumbers, melons, radishes, and tomatoes.
Oats: They grow very quickly for quick tilling to add organic matter to beds, and work well when planted with clover or vetch. An excellent source of green matter for the compost.
Onions: Plant chamomile and summer savory near onions to improve their flavour. Onions also work well alongside beets, Brassicas, carrots, dill, kohlrabi, leeks, lettuce, strawberries and tomatoes. Don’t plant onions near asparagus, onions or peas.
Oregano & Marjoram: Good for repelling cabbage moths, can be planted between rows of Brassicas for this purpose. It’s also good near asparagus and basil.
Parsley: Parsley likes asparagus, carrots, chives, corn, onions, and tomatoes. The leaves can be sprinkled on asparagus to repel asparagus beetles, and around roses, to improve their scent. Parsley allowed to bloom will attract hoverflies and predatory wasps. Don’t plant it near mint.
Peas: Good companions for beans, carrots, celery, corn, cucumber, eggplant, parsley, peppers, potatoes, radish, spinach, strawberries and turnips. Avoid planting peas near onions.
Peppers: Good neighbours for asparagus, basil, carrots, cucumbers, eggplant, endive, oregano, parsley, rosemary, squash, Swiss chard, and tomatoes. Never plant them next to beans or Brassicas.
Potatoes: Bush beans, Brassicas, carrots, celery, corn, garlic, marigolds, onions, and peas all do well planted near potatoes. Avoid planting potatoes near asparagus, cucumber, kohlrabi, melons, parsnips, rutabaga, squash, sunflower, and turnips.
Radish: Plant radishes near beans, beets, celeriac, chervil, cucumber, lettuce, mint, parsnip, peas, spinach, squash, and tomatoes. Avoid planting near Agastache or potatoes.
Rosemary: Good companion for beans, Brassicas, and carrots.
Fall Rye: Emits a chemical that inhibits the germination of weed seeds. Planted twice in a row, it can choke out several tough weed species. It produces masses of useful organic matter for tilling under or adding to the compost.
Sage: Repels both the cabbage moth and the carrot rust fly, so it’s a great all around companion plant in the vegetable garden. Do not, however, plant it near cucumbers, which are sensitive to aromatic herbs.
Spinach: Good companion for Brassicas, eggplants, leeks, lettuce, peas, radish, and strawberries, particularly. Don’t plant spinach near potatoes.
Squash: Good with corn, lettuce, melons, peas, and radish. Avoid planting near Brassicas or potatoes. Borage is said to improve the growth and flavour of squash. Marigolds and nasturtium repel numerous squash pest insects.
Strawberry: Plant with beans, borage, garlic, lettuce, onions, peas, spinach, and thyme. Avoid Brassicas, fennel, and kohlrabi.
Summer Savory: Attracts honeybees, and repels cabbage moths. Planting it near beans and onions will improve the flavour of both.
Sunflower: Plant near rows of corn to increase yields. Aphids may be herded by ants onto sunflowers without causing the plants any harm.
Swiss chard: Beans, Brassicas, and onions make the best companions.
Thyme: All around beneficial plant for the garden. Thyme is great planted near Brassicas and strawberries as it repels cabbage moths and enhances flavour.
Tomatoes: Companions are asparagus, basil, beans, borage, carrots, celery, chives, collards, cucumber, garlic, lettuce, marigold, mint, nasturtium, onion, parsley, and peppers. But not Brassicas, kohlrabi and dill. Corn will attract tomato pests. Potatoes can spread blight to tomatoes, keep them apart. Don’t plant tomatoes near walnut trees.
Turnip: Benefits from mint and pea companions.
Refer to this amazing visual chart detailing what does and doesn’t go together.
The infograghic is from Afristar Foundation