Companion planting

These peoples domesticated squash 8,000 to 10,000 years ago,[2][3] then maize, then common beans, forming the Three Sisters agricultural technique.

They host a cyanobacterium (Anabaena azollae) that fixes nitrogen from the atmosphere, and they block light from plants that would compete with the rice.

[11] More recently, starting in the 1920s, organic farming and horticulture have made frequent use of companion planting, since many other means of fertilizing, weed reduction and pest control are forbidden.

[13] The list of companion plants used in such systems is large, and includes vegetables, fruit trees, kitchen herbs, garden flowers, and fodder crops.

[14][15] In 2022, agronomists recommended that multiple tools including plant disease resistance in crops, conservation of natural enemies (parasitoids and predators) to provide biological pest control, and companion planting such as with aromatic forbs to repel pests should be used to achieve "sustainable" protection of crops.

They considered a multitrophic approach that took into account the many interactions between crops, companion plants, herbivorous pests, and their natural enemies essential.

[19] Other benefits, depending on the companion species used, include fixing nitrogen, attracting beneficial insects, suppressing weeds, reducing root-damaging nematode worms, and maintaining moisture in the soil.

[26] S. Finch and R. H. Collier, in a paper entitled "Insects can see clearly now the weeds have gone", showed experimentally that flying pests are far less successful if their host-plants are surrounded by other plants or even "decoy-plants" coloured green.

[27] Companion planting of clover as ground cover was equally disruptive to eight pest species from four different insect orders.

[30] Some companion plants help prevent pest insects or pathogenic fungi from damaging the crop, through their production of aromatic volatile chemicals, another type of allelopathy.

[33] In horticulture, marigolds provide good protection to tomato plants against the greenhouse whitefly (an aphid), via the aromatic limonene that they produce.

[38] Some companion herbs that produce aromatic volatiles attract natural enemies, which can help to suppress pests.

A 2019 field study in Brazil found that companion planting with parsley among a target crop of collard greens helped to suppress aphid pests (Brevicoryne brassicae, Myzus persicae), even though it also cut down the numbers of parasitoid wasps.

Companion planting of carrots and onions. The onion smell puts off carrot root fly, while the smell of carrots puts off onion fly. [ 1 ]
Multiple interactions between companion plants, target crops, weeds, pests , and beneficial insects such as parasitoids and predators of the pests make a multitrophic approach necessary. [ 16 ]
Some of the many mechanisms by which polyculture including companion planting may help to protect crops or otherwise increase productivity [ 19 ]
Root nodules of legumes fix nitrogen, assisting the growth of nearby plants.
Companion planting of cornflowers among cabbages helps the parasitoid wasp Microplitis mediator (shown) to control cabbage moth .
Spearmint attracts the mirid bug Nesidiocoris tenuis , an active predator that helps to suppress crop pests. [ 37 ]
Shade-grown coffee plantation in Costa Rica . The red trees in the background provide shade; those in the foreground have been pruned to allow full exposure to the sun.