Every year I max out companion planting (aka intercropping) my raised garden beds to help with organic pest control.
The idea behind companion planting is that certain plants help others by excreting substances from their roots, steer damaging insects away from food crops or ornamentals, or serve as homes to beneficial insects which prey on unwanted pests. Some consider this folk wisdom, as horticulturists and botanists have spent little time actually testing these theories. However, as a lifelong gardener, I can attest that my vegetables and fruit seem to have better growing seasons when I incorporate companion plants than when I don’t.
Planted among my sweet corn are bush beans, cantaloupe, nasturtiums, marigolds and cucumbers; pole beans are planted with cauliflower and nasturtium; three varieties of tomatoes are planted with peppers, garlic, onions, carrots, basil, and parsley (and nasturtiums and marigolds again). Potatoes are planted with nasturtiums. Sweet Potatoes sort of move in on everybody as their vines spread like tentacles across half of the garden. Sunflowers of all sizes border the garden to keep birds and squirrels occupied and raspberry bushes are planted along the South border. Daylilies and Gladiolas inhabit the West border. And wildflowers like Bachelor’s Buttons and Zinnias line the rabbit fence to attract pollinators.
I have barely a square inch of earth unplanted and I have few if any pest problems. Birds love the sunflower seeds and perch on top to spy crawling insects in the garden. After a rain, the garden is covered with birds looking for a quick meal and I have little crop damage from my flying friends.
Mother Earth News has an excellent list of companion plants here.