here is a fairly complete Companion Planting guide.
 
 A companion planting guide: which vegetables and flowers support or inhibit the growth of other plants and/or which pests they deter.
 
 Basil
 
 Plant near: most garden crops
 Keep away from: rue
 Comments: improves the flavor and growth of garden crops, especially tomatoes and lettuce. Repels mosquitoes.
 
 Beans, Bush
 
 Plant near: beets, cabbage, carrots, catnip, cauliflower, corn, cucumbers, marigolds, potatoes, savory, strawberries
 Keep away from: fennel, garlic, leeks, onions, shallots
 Comments: potatoes and marigolds repel Mexican bean beetles. Catnip repels flea beetles.
 
 Beans, Pole
 
 Plant near: corn, marigolds, potatoes, radishes
 Keep away from: beets, garlic, kohlrabi, leeks, onions, shallots
 Comments: same as for bush beans.
 
 Beets
 
 Plant near: broccoli, brussels sprouts, bush beans, cabbage, cauliflower, chard, kohlrabi, onions
 Keep away from: charlock, field mustard, pole beans
 
 Borage
 
 Plant near:  squash, strawberries, tomatoes
 Keep away from: can be planted along with any others
 Comments: repels tomato worms. Improves flavor and growth of companions.
 
 Broccoli and Brussels Sprouts
 
 Plant near: beets, buckwheat, calendula, carrots, chamomile, dill, hyssop, marigolds, mints, nasturtiums, onions, rosemary, sage, thyme, wormwood.
 Keep away from: strawberries
 Comments: marigolds repel cabbage moths. Nasturtiums repel aphids.
 
 Cabbage and Cauliflower
 
 Plant near: broccoli, brussels sprouts, celery, chard, spinach, tomatoes.
 Keep away from: strawberries
 Comments: tomatoes and celery repel cabbage worms.
 
 Cantaloupe
 
 Plant near: corn
 Keep away from: can be planted along with any others
 
 Carrots
 
 Plant near: cabbage, chives, early potatoes, leeks, lettuce, onions, peas, radishes, rosemary, sage, salsify, wormwood.
 Keep away from: can be planted along with any others
 Comments: onions, leeks, and wormwood repel carrot flies
 
 Chives
 
 Plant near: apples, berries, carrots, grapes, peas, roses, tomatoes.
 Keep away from: can be planted along with any others
 Comments: Improves flavor and growth of companions. Deters aphids and Japanese beetles.
 
 Corn
 
 Plant near: beans, cucumbers, early potatoes, melons, peas, pumpkins, soybeans, squash.
 Keep away from: can be planted along with any others
 Comments: soybeans deter chinch bugs.
 
 Cucumbers
 
 Plant near: beans, cabbage, corn, early potatoes, radishes, sunflowers.
 Keep away from: late potatoes
 Comments: Radishes deter cucumber beetles. Cucumbers encourage blight in late potatoes.
 
 Dill
 
 Plant near: broccoli, brussels sprouts, cabbage, cauliflower, cucumber, lettuce, onions
 Keep away from: carrots
 Comments: Improves flavor and growth of cabbage family plants.
 
 Epplant
 
 Plant near: green beans, peppers, potatoes, tomatoes
 Keep away from: can be planted along with any others
 Comments: green beans deter Colorado potato beetles.
 
 Garlic
 
 Plant near: cabbage, cane fruits, fruit trees, roses, tomatoes
 Keep away from: peas, beans
 Comments: deters Japanese beetles and aphids. A garlic oil spray deters onion flies, aphids, and ermine moths. A garlic tea helps repel late potato blight.
 
 Kale
 
 Plant near: aromatic herbs, buckwheat, cabbage family, marigolds, nasturtiums
 Keep away from: pole beans, strawberries
 
 Kohlrabi
 
 Plant near: cabbage/cauliflower companions (except tomatoes)
 Keep away from: fennel, pole beans, tomatoes
 Comments: kohlrabi stunts tomatoes
 
 Lettuce
 
 Plant near: beets, carrotsparsnips, radishes, strawberries
 Keep away from: cabbage family
 Comments: lettuce tenderizes summer radishes.
 
 Marigolds
 
 Plant near: all garden crops
 Keep away from: can be planted along with any others
 Comments: stimulates vegetable growth and deters bean beetles, aphids, potato bugs, squash bugs, nematodes, and maggots.
 
 Marjoram
 
 Plant near: all garden crops
 Keep away from: can be planted along with any others
 Comments: stimulates vegetable growth.
 
 Mustard
 
 Plant near: alfalfa cover crops, fruit trees, grapes, legumes
 Keep away from: can be planted along with any others
 Comments: stimulates growth of companion plants.
 
 Nasturtiums
 
 Plant near: apples, beans, cabbage family, greenhouse crops, potatoes, pumpkins, radishes, squash
 Keep away from: can be planted along with any others
 Comments: repels aphids, potato bugs, squash bugs, striped pumpkin beetles, and Mexican bean beetles and destroys white flies in greenhouses.
 
 Onions
 
 Plant near: beets, cabbage family, carrots, chamomile, lettuce, parsnips
 Keep away from: beans, peas
 Comments: deters most pests, especially maggots.
 
 Oregano
 
 Plant near: all garden crops
 Keep away from: can be planted along with any others
 Comments: deters many insect pests.
 
 Parsley
 
 Plant near: corn, roses, tomatoes
 Keep away from: can be planted along with any others
 
 Parsnips
 
 Plant near: onions, radishes, wormwood
 Keep away from: can be planted along with any others
 Comments: onions and wormwood help keep root maggots from parsnips.
 
 Peas
 
 Plant near: beans, carrots, corn, cucumbers, early potatoes, radishes, turnips
 Keep away from: garlic leeks, onions, shallots
 
 Peppers
 
 Plant near: basil, carrots, eggplant, onions, parsley, tomatoes
 Keep away from: fennel, kohlrabi
 
 Potatoes
 
 Plant near: basil, beans, cabbage family, corn, eggplant, 
flax, hemp, marigolds, peas, squash
 Keep away from: apples, birch, cherries, cucumbers, pumpkins, raspberries, sunflowers, tomatoes, walnuts
 Comments: hemp deters phytophthora infestans. Basil deters potato beetles. Marigolds (dug into crop soil) deter nematodes.
 
 Radishes
 
 Plant near: chervil, cucumbers, lettuce, melons, peas, nasturtiums, root crops
 Keep away from: hyssop
 Comments: radishes deter cucumber beetles. Chervil makes radishes hot. Lettuce helps make radishes tender. Nasturtiums improve radishes' flavor.
 
 Rosemary
 
 Plant near: beans, cabbage, carrots
 Keep away from: can be planted along with any others 
 Comments: repels bean beetles, cabbage moths, and carrot flies.
 
 Sage
 
 Plant near: cabbage family, carrots, tomatoes
 Keep away from: cucumbers
 Comments: deters cabbage moths and carrot flies. Invigorates tomato plants.
 
 Soybeans
 
 Plant near: corn, potatoes
 Keep away from: can be planted along with any others
 Comments: chokes weeds and enriches soil.
 
 Spinach
 
 Plant near: celery, cauliflower, eggplant, strawberries
 Keep away from: can be planted along with any others
 
 
 Strawberries
 
 Plant near: borage, bush beans, lettuce, pyrethrum, spinach
 Keep away from: cabbage family
 
 
 Sunflowers
 
 Plant near: cucumbers
 Keep away from: potatoes
 Comments: can provide a trellis and shelter for shade-loving cucumbers.
 
 Swiss Chard
 
 Plant near: bush beans, kohlrabi, onions
 Keep away from: pole beans
 
 
 Tarragon
 
 Plant near: all garden crops
 Keep away from: can be planted along with any others
 Comments: improves vegetables' flavor and growth.
 
 Thyme
 
 Plant near: all garden crops
 Keep away from: can be planted along with any others
 Comments: deters cabbage moths.
 
 Tomatoes
 
 Plant near: asparagus, basil, cabbage family, carrots, gooseberries, mustard, parsley, onions, rosemary, sage, stinging nettles
 Keep away from: fennel, kohlrabi, potatoes, walnuts
 
 
 Turnips and Rutabagas
 
 Plant near: peas
 Keep away from: knotweed, mustard
 Comments: mustard and knotweed inhibit the growth of turnips and rutabagas.