Companion planting in gardening and agriculture is planting of different crops in close physical proximity. It is a form of polyculture.
Companion planting is used by farmers, and gardeners in both the industrialised world as well as the third world.
In the third world, tropical crops are used instead of temperate ones and provide NGO's, and other organizations a tool for allowing the poor to get out of poverty.
For gardeners, the combinations of plants also make for a more varied, attractive vegetable garden. It can also be used to mitigate the decline of biodiversity. Many of the modern principles of companion planting were present many centuries ago in the cottage garden.
Companion planting was widely touted in the 1970s as part of the organic gardening movement. It was encouraged not for pragmatic reasons like trellising, but rather with the idea that different species of plant may thrive more when close together. It is also a technique frequently used in permaculture, together with mulching, polyculture, and changing of crops.
One traditional practice was planting of corn (maize) and pole beans together. The cornstalk would serve as a trellis for the beans to climb. The inclusion of squash with these two plants completes the Three Sisters technique, pioneered by Native American peoples.
Nasturtium are well-known to attract caterpillars, so planting them alongside or around vegetables such as lettuce or cabbage will protect them, as the egg-laying insects will tend to prefer the nasturtium.
Crops which suffer from greenfly and other aphids may benefit from the proximity of marigolds: these attract hoverflies, a predator of aphids, and are also said to deter other pests. A more complete list of plants that deter insects is listed below.
The use of plants that produce copious nectar and protein-rich pollen in a vegetable garden (insectary plants) is a good way to enhance the population of beneficial insects that control pests. Some insects in the adult form are nectar or pollen feeders, while in the larval form they are voracious predators of pest insects.
There are a number of systems and ideas utilizing companion planting.
Square foot gardening, for example, attempts to protect plants from many normal gardening problems by packing them as closely together as possible, which is facilitated by using companion plants, which can be closer together than normal.
Another system utilizing companion planting is that of the forest garden, where companion plants are intermingled to create an actual ecosystem, emulating the interaction of up to seven levels of plants in a forest or woodland.
Organic gardening often depends on companion planting for its best performance, since so many synthetic means of fertilizing, weed reduction, pest control, and other garden needs are forbidden.
There are many beneficial weeds, which can be allowed to grow alongside plants, imparting the very same kinds of benefits as mixing cultivated crops.
Companion Plant Categories
Companion plants can benefit each other in a number of different ways, including:
- Flavor enhancement — some plants, especially herbs, seem to subtly change the flavor of other plants around them.
- Hedged investment — multiple plants in the same space increase the odds of some yield being given, even if one category encounters catastrophic issues
- Level interaction — plant
s which grow on different levels in the same space, perhaps providing ground cover or working as a trellis for another plant
- Nitrogen fixation — plants which fix nitrogen in the ground, making it available to other plants
- Pest suppression — plants which repel insects, plants, or other pests like nematodes or fungi, through chemical means
- Positive hosting — attracts or is inhabited by insects or other organisms which benefit plants, as with ladybugs or some "good nematodes"
- Protective shelter — one plant type of plant may serve as a wind break, or shade from noonday sun, for another
- Trap Cropping — plants which attract pests away from others