Companion planting in gardening and agriculture is the planting of different crops in proximity for any of a number of different reasons, including pest control,

pollination Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, ...

, providing

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

for

beneficial insect Beneficial insects (sometimes called beneficial bugs) are any of a number of species of insects that perform valued services like pollination and pest control. The concept of ''beneficial'' is subjective and only arises in light of desired outcome ...

s, maximizing use of space, and to otherwise increase crop productivity. Companion planting is a form of

polyculture In agriculture, polyculture is the practice of growing more than one crop species in the same space, at the same time. In doing this, polyculture attempts to mimic the diversity of natural ecosystems. Polyculture is the opposite of monoculture, ...

. Companion planting is used by farmers and gardeners in both industrialized and developing countries for many reasons. Many of the modern principles of companion planting were present many centuries ago in forest gardens in Asia, and thousands of years ago in

Mesoamerica Mesoamerica is a historical region and cultural area in southern North America and most of Central America. It extends from approximately central Mexico through Belize, Guatemala, El Salvador, Honduras, Nicaragua, and northern Costa Rica ...

History

In China, mosquito ferns (''Azolla'' spp.) have been used for at least a thousand years as companion plants for

rice Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly '' Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and ''Porteresia'', both wild and domesticate ...

crops. They host a

cyanobacterium Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue ...

(''Anabaena azollae'') that fixes nitrogen from the atmosphere, and they block light from plants that would compete with the rice. Companion planting was practiced in various forms by the

indigenous peoples of the Americas The Indigenous peoples of the Americas are the inhabitants of the Americas before the arrival of the European settlers in the 15th century, and the ethnic groups who now identify themselves with those peoples. Many Indigenous peoples of the Am ...

prior to the arrival of Europeans. These peoples domesticated squash 8,000 to 10,000 years ago, then

maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn ( North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. T ...

, then

common bean ''Phaseolus vulgaris'', the common bean, is a herbaceous annual plant grown worldwide for its edible dry seeds or green, unripe pods. Its leaf is also occasionally used as a vegetable and the straw as fodder. Its botanical classification, alo ...

s, forming the Three Sisters agricultural technique. The cornstalk served as a trellis for the beans to climb, the beans fixed nitrogen, benefitting the maize, and the wide leaves of the squash plant provide ample shade for the soil keeping it moist and fertile.

Practice

More recently, starting in the 1920s,

organic farming Organic farming, also known as ecological farming or biological farming,Labelling, article 30 o''Regulation (EU) 2018/848 of the European Parliament and of the Council of 30 May 2018 on organic production and labelling of organic products and re ...

and

horticulture Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...

have made frequent use of companion planting, since many other means of fertilizing, weed reduction and pest control are forbidden. The list of companion plants used in such systems is large, and includes vegetables, fruit trees, kitchen herbs, garden flowers, and fodder crops. The number of interactions both positive (the pair of species assist each other) and negative (the plants are best not grown together) is also large, though the evidence for such interactions ranges from controlled experiments to hearsay. For example, plants in the cabbage family ( Brassicaceae) grow well with celery, onion family plants (''

Allium ''Allium'' is a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives. The generic name ''Allium'' is the Latin word for garlic,Gledhill, David ...

''), and aromatic herbs, but are best not grown with strawberry or tomato.

Mechanisms

Companion planting can operate through a variety of mechanisms, which may sometimes be combined. These include pest control,

, providing

for

s, and maximizing use of space; all of these may help to increase crop productivity. excerpted from

Nutrient provision

Legumes such as

clover Clover or trefoil are common names for plants of the genus ''Trifolium'' (from Latin ''tres'' 'three' + ''folium'' 'leaf'), consisting of about 300 species of flowering plants in the legume or pea family Fabaceae originating in Europe. The genus ...

provide nitrogen compounds to neighbouring plants such as grasses by fixing nitrogen from the air with symbiotic bacteria in their root nodules. These enable the grasses or other neighbours to produce more protein and hence to grow more.

Trap cropping

Trap crop A trap crop is a plant that attracts agricultural pests, usually insects, away from nearby crops. This form of companion planting can save the main crop from decimation by pests without the use of pesticides. /sup> A trap crop is used for attracti ...

ping uses alternative plants to attract pests away from a main crop. For example, nasturtium (''Tropaeolum majus'') is a food plant of some

caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder S ...

s which feed primarily on members of the cabbage family (brassicas); some gardeners claim that planting them around brassicas protects the food crops from damage, as eggs of the pests are preferentially laid on the nasturtium. However, while many trap crops divert pests from focal crops in small scale greenhouse, garden and field experiments, only a small portion of these plants reduce pest damage at larger commercial scales.

Host-finding disruption

Flying pests are far less successful if their host-plants are surrounded by other plants or even "decoy-plants" coloured green. Pests find hosts in stages, first detecting plant odours which induce it to try to land on the host plant, avoiding bare soil. If the plant is isolated, then the insect simply lands on the patch of green near the odour, making an "appropriate landing". If it finds itself on the wrong plant, an "inappropriate landing", it takes off and flies to another plant; it eventually leaves the area if there are too many "inappropriate" landings. Companion planting of

as ground cover was equally disruptive to eight pest species from four different insect orders. In a test, 36% of cabbage root flies laid eggs beside cabbages growing in bare soil (destroying the crop), compared to only 7% beside cabbages growing in clover (which allowed a good crop). Simple decoys of green cardboard worked just as well as the live ground cover.

Pest suppression

Some companion plants help prevent pest insects or pathogenic

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

from damaging the crop, through chemical means. For example, the smell of the foliage of marigolds is claimed to deter

aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A ...

s from feeding on neighbouring plants. A 2005 study found that oil volatiles extracted from Mexican marigold by vacuum distillation reduced the reproduction of three aphid species ( pea aphid, green peach aphid and glasshouse and potato aphid) by up to 100% after 5 days from exposure. Another example familiar to gardeners is the interaction of onions and carrots with each other's pests: the onion smell puts off carrot root fly, while the smell of carrots puts off onion fly.

Predator recruitment

Companion plants that produce copious nectar or

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametoph ...

in a vegetable garden ( insectary plants) may help encourage higher populations of

s that control pests.

Protective shelter

Some crops are grown under the protective shelter of different kinds of plant, whether as wind breaks or for shade. For example, shade-grown coffee, especially '' Coffea arabica'', has traditionally been grown in light shade created by scattered trees with a thin canopy, allowing light through to the coffee bushes but protecting them from overheating. Suitable Asian trees include ''

Erythrina subumbrans ''Erythrina subumbrans'' is a flowering plant species in the genus ''Erythrina ''Erythrina'' is a genus of plants in the pea family, Fabaceae. It contains about 130 species, which are distributed in tropical and subtropical regions worldwide. ...

'' (tton tong or dadap), '' Gliricidia sepium'' (khae falang), '' Cassia siamea'' (khi lek), ''

Melia azedarach ''Melia azedarach'', commonly known as the chinaberry tree, pride of India, bead-tree, Cape lilac, syringa berrytree, Persian lilac, Indian lilac, or white cedar, is a species of deciduous tree in the mahogany family, Meliaceae, that is nati ...

'' (khao dao sang), and ''

Paulownia tomentosa ''Paulownia tomentosa'', common names princess tree, empress tree, or foxglove-tree, is a deciduous hardwood tree in the family Paulowniaceae, native to central and western China. It is an extremely fast-growing tree with seeds that disperse re ...

'', a useful timber tree.

Approaches

Companion planting approaches in use or being trialled include: * Square foot gardening attempts to protect plants from issues such as weed infestation by packing them as closely together as possible. This is facilitated by using companion plants, which can be closer together than normal. * Forest gardening, where companion plants are intermingled to simulate an ecosystem, emulates the interaction of plants of up to seven different heights in a

woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ''plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (see ...

.. See also

References

{{Permaculture Sustainable gardening Permaculture Crops Biological pest control Sustainable technologies Chemical ecology