Complementary vegetable plants benefit those they are planted next to. Also called companion planting, accomplish pest control, advanced flavor, shading and higher yield just by knowing what vegetable plants complement each other. There are also instances when plants growing in close proximity will harm each other. For instance, kohlrabi and tomato planted closely together will stunt each other's growth.
Tomatoes benefit from being planted near asparagus, cucumber, carrot, onion, celery, parsley and pepper plants. Be careful not to plant corn near tomatoes as they are attacked by the same worm. Tomatoes and potatoes don't complement each other as both are susceptible to the same blight. Kohlrabi, planted too close to tomatoes will stunt tomato growth.
Peas do very well planted 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 grows well when it lives next to any of the member of the cabbage family. Beets, carrots, onions, radishes or even strawberry plants are good garden neighbors for lettuce. Reduce the chance of aphids feasting on lettuce plants by planting chives or garlic nearby.
Give pepper plants an added boost by planting them next to plants that will help them grow. Complementary vegetable plants for peppers are onion, tomato, carrot and eggplant.
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 in the vegetable garden.
Radishes grow well alongside lettuce, peas, beans and cucumber. They are also complemented by a planting of carrots.
Chives will improve the flavor and growth of carrots. Other complementary plants for carrots are onion, 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.
Bean, corn and tomato plants are all good neighbors for the cucumber. All members of the cabbage family and radishes are also good companion plants. Cucumber plants don't do well if planted near sage, but oregano will keep insects away. If the cucumber plants attract beetles, aphids or other bugs, plant marigold or nasturtium nearby.