Companion planting is an organic gardening design concept that recognizes plants' abilities to keep each other healthier and produce more abundant crops when they are placed together in the garden plot. Vegetables, herbs and flowers all possess these traits. Controlling pests is one of the most important benefits of a garden design that incorporates companion planting strategies. Plants accomplish this natural pest control by attracting beneficial insects that eat the harmful ones, and through chemicals their roots put into the soil.
Plant peas and beans, starting at the north side of the garden. They will grow tall enough to provide partial shade for lettuce, kale and spinach, which allows these vegetables to keep producing even when the spring weather goes from mild to hot. Peas and beans contribute nitrogen to the soil, which helps kale and spinach thrive. Plant the fragrant herb rosemary near the bean rows to deter invasive bean beetles.
Divide the next section of the garden in half, planting carrots, onions and leeks in successive rows on one side. The nearby rosemary will keep carrot flies away. Leeks help both the carrots and onions grow faster, and prevent onion flies from getting established.
Plant eggplant and peppers on the other side of this section. These make good companions because they boost each other's growth rate. The purple eggplants provide interesting visual contrast with the green, red or yellow peppers.
Plant tomatoes, continuing down the garden plot in a southerly direction. Put in a row of herb borage. Besides adding the beauty of its blue flowers, borage provides trace elements of minerals that promote growth in tomatoes and squash. Squash and cucumbers go in next. Then plant one or two rows of radishes, at the southern end of your garden. Radishes are a deterrent to both squash borers and cucumber beetles.
Plant marigolds along the east and west borders of the garden. They have the remarkable ability to release chemical compounds that prevent below ground pests from spreading across the garden soil. Garlic can provide the same benefit.