Planting Companions

The interactions between garden plants have not been extensively studied in carefully controlled trials, so there isn’t much hard scientific data on the abilities of different species to help (or hurt) each other when they’re grown close together. But over the years, gardeners’ observations have formed a body of advice that’s impressive enough to be worth some consideration.

A lot of the tried and true is just common sense. Plants with strong odors — such as basil, rue, marigold, scented-leaf geraniums, and garlic — repel or confuse many insects that rely on smells to find their targets. Herbs and flowers loved by bees — such as borage, thyme, and bee balm — help attract these pollinators and thus improve fruit-set on many vegetables, including summer and winter squash, tomatoes, peppers, and beans.

There are also many specific combinations that are famous, at least in folklore, though as the diet advertisements say, “results may vary.” Much will depend on climatic conditions, the nature of the soil, and the overall health of the plants in question. Nevertheless, more than a few gardeners swear by rules like these:

• Plant parsley near asparagus to improve vigor
• Radishes grown near lettuce are more tender
• Petunias help repel bean beetles
• Beets interplanted with onions will help stifle weeds
• Carrots will grow larger if interplanted with chives
• Dill or caraway will help repel cabbage moths
• Tomatoes hate fennel; keep them apart
• Beans don’t do well near alliums (garlic, onions, chives)
• Nasturtiums attract aphids and deter cucumber and bean beetles

In nature plants are gregarious, living in complex communities. Short, early bloomers share space with tall species that leaf out and flower late; shallow-rooted types cozy up to deep-rooted neighbors. Heavy feeders benefit from association with plants that make more nutrients than they themselves need.

And because each piece of ground hosts a diversity of species, pests and diseases (which tend to target particular groups of plants) are naturally limited; there’s never enough of any one thing to support major infestation.

Vegetable gardens can’t be as intricate as the natural patchwork, but they can take a lesson from it, and the more diversity they support, the more productive they will be.

• Plant vining crops like squash in the corn patch; the sprawling vines will provide a living mulch that conserves surface moisture (corn has shallow roots) and keeps down the weeds. Don’t plant the squash until the soil warms and the corn is about a foot tall. Corn likes toasty toes, and baby plants will be smothered unless they get a head start.
• Plant heavy feeders like squash, cucumber, corn, and celery next to — or right after — peas and beans, which fix nitrogen through their roots, improving the fertility of the soil under and around them.
• Once summer heat strikes, plant greens like lettuce and spinach on the shady side of tall pea and bean rows. The soil will be cooler there, and the extra nitrogen in the soil will help the leaves grow swiftly.
• Instead of planting a large bed of one crop, consider planting alternate rows. Bush beans work well with members of the cabbage family, for instance, and carrots get along well with determinate (short-vined) tomatoes.