Cultivating Good Relationships : Making Companions of Certain Plants Yields Tastier, Healthier Crops

Stop! Don’t plant beans next to those onions.

And wait! You need basil near those tomatoes.

As you plant your garden in the next few weeks, consider companion planting; placing certain plants next to certain other ones can help some plants grow more vigorously, improve the flavor of others, repel harmful insects and attract beneficial critters.

Research has found that companion planting does have its merits. “Some plants do repel insects and fulfill other functions in the yard, which results in improved growth of other plants,” says Kent Gordon, horticulture department coordinator at Fullerton College.

If you have a vegetable plant that needs to grow a great deal before fruiting, plant it next to a legume crop, such as beans or peas, Gordon says. “Beans and peas form colonies in their roots that actually draw nitrogen from the air,” he says. This nitrogen is then released into the soil, which builds its fertility and causes nearby plants to grow rapidly.

Good companion plants to beans and peas include heavy feeders such as cucumbers, eggplant, corn, lettuce, peppers and sweet corn.

Some people have also observed that certain plants improve the flavor of other plants when placed in proximity.

“When you plant basil near tomatoes it makes the tomatoes taste better,” says Ron LaFond of Westminster, who has used companion planting for a number of years.

“Summer savory adds to the flavor of beans and potatoes, while rosemary is also a good flavor-enhancer for a variety of plants,” says LaFond, who designs and installs landscapes and irrigation systems.

Some root crops are also good companion plants. They cultivate the soil, making root growth easier for other plants. Radishes are vigorous, fast growing plants that are especially good at cultivation. Carrots are another good choice.

While some plants grow well together, others should be kept at a distance. “Keep all legume crops such as bush beans, lima beans and sweet peas away from onion crops such as garlic, green onion, chives and scallions,” says LaFond. “At the moment, I have a 16-foot row of sweet peas growing next to a six-foot row of garlic and where the two meet the sweet peas are doing very poorly.”

LaFond also says to be careful of what you plant near fennel, because it will diminish the yield of many plants.

Companion planting is also a great way to rid your garden of unwanted insects. Many plants are good pest repellents.

One plant at the top of the pest-deterrent list is the strong-scented marigold. “These flowers release an oil that gets onto other plants and discourages pests,” says Chuck Bybee of Armstrong Garden Center in Santa Ana. Insects turned off by the marigold are Mexican bean beetles, aphids and Colorado potato beetles.

Below ground, marigolds also deter nematodes, the soil flatworms that attach themselves to plant roots and root crops, causing distortions, holes and knots. When a plant dies for no apparent outward reason, they are often at fault.

“The roots of the marigolds excrete a chemical that kills bad nematodes on contact, but doesn’t hurt beneficial nematodes because they don’t eat roots,” Bybee says.

To fully benefit from marigolds, it is best to till them into your garden once they are done producing, which will cause the chemical to build up in your soil. Be aware that it takes some time for the chemical to accumulate in the soil, Gordon says.

Marigolds are also a good deterrent of another garden irritant--snails. “Snails will avoid them, so try putting a ring of marigolds around your garden to act as a barrier,” says Gordon.

Another strong-smelling plant disliked by insects is, surprisingly, the tomato. This plant offends the flea beetle that bothers cabbage, and tomatoes exude a chemical that repels the carrot root maggot, according to LaFond. Tomato foliage is so potent, some people even use ground-up leaves as an insecticide.

“Some pests also find spinach offensive because it releases the chemical saponin,” LaFond says. “It does its job best if the plant remnants are mulched into the soil. As the spinach breaks down in the ground, it repels insects.”

French tarragon is another fragrant herb good at repelling insects, according to LaFond, while spearmint and tansy are great at discouraging ants, Bybee says.

“It’s a good idea to keep ants out of your garden because they are notorious aphid herders,” Bybee says. “Here at the nursery we recently discovered ants carrying aphids to an artichoke plant.”

Another group of strong-smelling plants that are very good at deterring certain pests are those in the onion family, which all do a good job at stopping the carrot fly from wreaking havoc. Garlic also deters aphids.

“When planting these onion family crops, it’s best to inter-plant them among your garden where they are more likely to be brushed and bruised as you pass them,” Bybee says. “This causes their strong odors to be released, which confuses pests who will then stay away from the entire area.”

Plants that prevent insect damage include white icicle radishes, which should be planted around squash, and cucumbers, since they keep the squash borers out, LaFond says. “Potatoes and bush beans are also good companion plants, because bush beans repel the Colorado potato beetle, and the potato turns off the Mexican bean beetle,” he says.

Another way to keep pests away is to use certain plants as “traps.” This method of companion planting involves planting plants that insects favor more than your desired crops. For instance, marigolds attract spider mites, nasturtiums lure aphids and spearmint attracts various flies and spiders.

Do not, however, let the plants get so overladen with pests that they move to your desired crop.

“When the trap is full, pull it out and throw it away,” says Bybee.

There are many companion plants that will attract beneficial insects to your garden, which in turn rid your yard of unwanted pests. According to Bybee, such plants include the herb tansy, which he says can be purchased in four-inch pots; spearmint, which can be grown from seed or purchased in four-inch pots; zinnias, which can be found in pots or may be direct seeded, and cosmos, which can also be found in the nursery in four-inch pots.

“All of these plants are in the same family and attract certain flies and parasitic wasps and spiders, which will eat other insects,” Bybee says.

Another group of plants that also attract good insects are dill, which attracts aphid predators and parasites; fennel, which lures hover flies and parasitic wasps; sunflowers, which entice lacewings and parasitic wasps, and yarrow, which attracts hover flies, lady beetles and parasitic wasps. You should be able to find seeds for these plants in the nursery or through a mail order catalogue.