Parsnips

Plant near: onions, radishes, wormwood
Extra tips: onions and wormwood help keep root maggots from parsnips.

 Peas

Plant near: beans, cucumbers, early potatoes, radishes, turnips carrots, corn
Keep away from: garlic leeks, onions, shallots

Onions

Plant near: carrots, chamomile, beets, cabbage family, lettuce, parsnips
Keep away from: beans, peas
Extra tips: deters most pests, especially maggots.

 Oregano

Plant near: all garden crops
Extra tips: deters many insect pests.

Parsley

Plant near: corn, roses, tomatoes

 Peppers

Plant near: onions, parsley, tomatoes, basil, carrots, eggplant
Keep away from: fennel, kohlrabi

 Potatoes

Plant near: corn, eggplant, flax, hemp, marigolds, peas, squash, basil, beans, cabbage family
Keep away from: cucumbers, pumpkins, raspberries, sunflowers, tomatoes, walnuts, apples, birch, cherries,
Extra tips: hemp deters phytophthora infestans. Basil deters potato beetles. Marigolds (dug into crop soil) deter nematodes.

 Radishes

Plant near: lettuce, melons, peas, nasturtiums, root crops, chervil, cucumbers
Keep away from: hyssop
Extra tips: radishes deter cucumber beetles. Chervil makes radishes hot. Lettuce helps make radishes tender. Nasturtiums improve radishes’ flavor.

 Soybeans

Plant near: corn, potatoes
Keep away from:
Extra tips: chokes weeds and enriches soil.

 Spinach

Plant near: celery, cauliflower, eggplant, strawberries

 Strawberries

Plant near: borage, bush beans, lettuce, pyrethrum, spinach
Keep away from: cabbage family
Extra tips: Mulching with or planting near fragrant herbs such as rosemary and mint will deter slugs.

Sunflowers
Plant near: cucumbers
Keep away from: potatoes
Extra tips: can provide a trellis and shelter for shade-loving cucumbers.

 Rosemary
Plant near: beans, cabbage, carrots
Keep away from:
Extra tips: repels bean beetles, cabbage moths, and carrot flies.

Tomatoes
Plant near: carrots, gooseberries, mustard, parsley, onions, rosemary, sage, stinging nettles, asparagus, basil, cabbage family
Keep away from: fennel, kohlrabi, potatoes, walnuts

 Turnips and Rutabagas

Plant near: peas
Keep away from: knotweed, mustard
Extra tips: mustard and knotweed inhibit the growth of turnips and rutabagas.

Sage

Plant near: cabbage family, carrots, tomatoes
Keep away from: cucumbers
Extra tips: deters cabbage moths and carrot flies. Invigorates tomato plants

Keep in mind that companion planting is not an exact science, and the knowledge of veteran gardeners in your area can be extremely favorable.

Source: www.realfarmacy.com
Other included sources linked in Real Farmacy’s article: Mother Earth News -- Original Article Source