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 Pest control is the regulation or management of a species defined as a pest; any animal, plant or fungus that impacts adversely on human activities or environment. The human response depends on the importance of the damage done and will range ...

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

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 domestica ...

crops. They host a cyanobacterium (''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 A ...

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. ...

, 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 Trellis may refer to: Structures * Trellis (architecture), an architectural structure often used to support plants (especially vineyards) * Trellis drainage pattern, a drainage system Technology * Trellis (graph), a special kind of graph used ...

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 This is a list of companion plants. Many more are in the list of beneficial weeds. Companion plants assist in the growth of others by attracting beneficial insects, repelling pests, or providing nutrients, shade, or support. They can be part o ...

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 Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The l ...

) 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, ...

''), 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

, providing

for beneficial insects, 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 h ...

provide nitrogen compounds to neighbouring plants such as grasses by fixing nitrogen from the air with symbiotic bacteria in their

root nodule Root nodules are found on the roots of plants, primarily legumes, that form a symbiosis with nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria know ...

s. These enable the grasses or other neighbours to produce more protein and hence to grow more.

Trap cropping

Trap cropping 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 larva, larval stage of members of the order Lepidoptera (the insect order comprising butterfly, butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawfly ...

s which feed primarily on members of the

cabbage family Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The leav ...

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

from damaging the crop, through chemical means. For example, the smell of the foliage of

marigold Marigold may refer to: * Marigold (color), a yellow-orange color It may also refer to: Plants * In the genus ''Calendula'': ** Common marigold, '' Calendula officinalis'' (also called pot marigold, ruddles, or Scotch marigold) * In the genus ' ...

s 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 Mexican marigold also known as , or Aztec marigold is a native flower to México and was first used by the Aztecs and is used in the Mexican holiday "Dia de los muertos" or day of the dead. Day of the dead originated from Aztec mythology to honor th ...

by vacuum distillation reduced the reproduction of three aphid species (

pea aphid ''Acyrthosiphon pisum'', commonly known as the pea aphid (and colloquially known as the green dolphin, pea louse, and clover louse), is a sap-sucking insect in the family Aphididae. It feeds on several species of legumes (plant family Fabaceae) w ...

green peach aphid ''Myzus persicae'', known as the green peach aphid, greenfly, or the peach-potato aphid, is a small green aphid belonging to the order Hemiptera. It is the most significant aphid pest of peach trees, causing decreased growth, shrivelling of the ...

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 The carrot fly (''Chamaepsila rosae'') is a pest of gardens and farms, and mainly affects the crop of carrots, but can also attack parsnips, parsley and celery. It is a member of the family Psilidae (order Diptera). Larvae Crop damage is cause ...

, while the smell of carrots puts off

onion fly ''Delia antiqua'', commonly known as the onion fly, is a cosmopolitan pest of crops. The larvae or maggots feed on onions, garlic, and other bulbous plants. Morphology and biology The onion fly has an ash-grey body and resembles a housefly. Th ...

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 gametop ...

in a vegetable garden ( insectary plants) may help encourage higher populations of beneficial insects 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 ''Coffea arabica'' (), also known as the Arabic coffee, is a species of flowering plant in the coffee and madder family Rubiaceae. It is believed to be the first species of coffee to have been cultivated and is currently the dominant cultivar, r ...

'', 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'' (tton tong or dadap), '' Gliricidia sepium'' (khae falang), '' Cassia siamea'' (khi lek), '' Melia azedarach'' (khao dao sang), and '' Paulownia tomentosa'', a useful timber tree.

Approaches

Companion planting approaches in use or being trialled include: *

Square foot gardening Square foot gardening is the practice of dividing the growing area into small square sections, typically on a side, hence the name. The aim is to assist the planning and creating of a small but intensively planted vegetable garden. It results ...

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