Complementary vegetable plants benefit those they are planted next to. Companion planting can control pests, enhance flavor, shade and produce a higher yield.
Tomatoes: Plant near pepper, onion, asparagus, cucumber, carrot, celery, and parsley plants.
Peas: Plant near bean, corn, carrot, cucumber, turnip and radish. Tuck in some chives near the peas to reduce aphids. (Keep garlic and onion plants at a distance, as both will stunt the growth of pea plants.)
Lettuce: Plant near cabbage varieties, beets, carrots, onions, radishes or strawberry plants. Reduce the chance of aphids feasting on lettuce plants by planting chives or garlic nearby.
Peppers: Plant near onion, tomato, carrot and eggplant to boost pepper plant growth.
*Corn: Plant corn alongside of beans, parsley, peas and potatoes—with a benefit to all. Squash, cucumber, melon and pumpkin plants are also complementary vegetable companions for corn. Tomatoes and corn are both attacked by the same worm, so avoid planting them too close together.
Radish: Plant alongside lettuce, peas, beans, carrots and cucumber.
Carrots: Chives will improve the flavor and growth of carrots. Also plant near lettuce, bean, pepper, radish, tomato and peas. Rosemary and sage will reduce the chance of carrot fly infestation. (Keep dill away from the carrot plants as it will retard growth.)
Cucumber: Bean, corn, cabbage varieties, radishes and tomato plants are all good neighbors for the cucumber. Oregano will keep insects away. If the cucumber plants attract beetles, aphids or other bugs, plant marigold or nasturtium nearby. (Cucumber plants don’t do well if planted near sage.)
*From what I have read, gardeners did not get as good of a return on investment by planting corn. People say they take too much time, money, and trouble. The number one return on investment seems to be berries, from the testimonies I have read online on various sites. According to strawberryplants.org, ten to twenty-five strawberry plants can often be purchased for less than $20.00 and can sometimes be found for closer to $10.00. Usually, 25 strawberry plants will adequately supply a family of four with strawberries. Just a few strawberry purchases in the grocery store will likely cost more.
Source: Complementary Vegetable Garden Plants | Garden Guides http://www.gardenguides.com/93382-complementary-vegetable-garden-plants.html#ixzz1qHoQEegL