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Companion planting

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Companion planting of carrots and onions. The onion smell puts off carrot root fly, while the smell of carrots puts off onion fly.[1]

Companion plantingin gardening and agriculture is the planting of different crops in proximity for any of a number of different reasons, includingweed suppression,pest control,pollination,providinghabitatforbeneficial insects,maximizing use of space, and to otherwise increasecrop productivity.Companion planting is a form ofpolyculture.

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 inforest gardensin Asia, and thousands of years ago inMesoamerica.The technique may allow farmers to reduce costly inputs of artificialfertilisersandpesticides.

Traditional practice[edit]

History[edit]

Companion planting was practiced in various forms by theindigenous peoples of the Americasprior to the arrival of Europeans. These peoples domesticatedsquash8,000 to 10,000 years ago,[2][3]then maize, thencommon beans,forming theThree Sistersagricultural technique. The cornstalk served as atrellisfor the beans to climb, the beansfixed nitrogen,benefitting the maize, and the wide leaves of the squash plant provide ample shade for the soil keeping it moist and fertile.[4][5][6]

Authors inclassical GreeceandRome,around 2000 years ago, were aware that some plants were toxic (allelopathic) to other plants nearby.[7]Theophrastusreported that thebay treeand the cabbage plant enfeebled grapevines.[8][9]Pliny the Elderwrote that the "shade" of the walnut tree (Juglans regia) poisoned other plants.[10][9]

In China,mosquito ferns(Azollaspp.) have been used for at least a thousand years as companion plants for rice crops. They host acyanobacterium(Anabaena azollae) that fixes nitrogen from the atmosphere, and they block light from plants that would compete with the rice.[11]

20th century[edit]

Further information:List of companion plants

More recently, starting in the 1920s,organic farmingandhorticulturehave made frequent use of companion planting, since many other means of fertilizing, weed reduction and pest control are forbidden.[12]Permacultureadvocates similar methods.[13]

Thelist of companion plantsused in such systems is large, and includes vegetables, fruit trees, kitchen herbs, garden flowers, and fodder crops. The number of pairwise interactions both positive (the pair of species assist each other) and negative (the plants are best not grown together) is larger, though the evidence for such interactions ranges fromcontrolled experimentsto hearsay. For example, plants in the cabbage family (Brassicaceae) are traditionally claimed to grow well with celery, onion family plants (Allium), and aromatic herbs, but are thought best not grown with strawberry or tomato.[14][15]

In 2022, agronomists recommended that multiple tools includingplant disease resistancein crops, conservation of natural enemies (parasitoidsandpredators) to providebiological pest control,and companion planting such as with aromatic forbs to repel pests should be used to achieve "sustainable" protection of crops. They considered amultitrophicapproach that took into account the many interactions between crops, companion plants,herbivorouspests, and their natural enemies essential.[16]Many studies have looked at the effects of plants on crop pests, but relatively few interactions have been studied in depth or using field trials.[17]

Multiple interactions between companion plants, target crops, weeds,pests,andbeneficial insectssuch asparasitoidsandpredatorsof the pests make amultitrophicapproach necessary.[16]

Mechanisms[edit]

Companion planting can help to increasecrop productivitythrough a variety of mechanisms, which may sometimes be combined. These includepollination,weed suppression,andpest control,including by providinghabitatforbeneficial insects.[18]

Companion planting can reduce insect damage to crops, whether by disrupting pests' ability to locate crops by sight, or by blocking pests physically; by attracting pests away from a target crop to a sacrificialtrap crop;or by masking the odour of a crop, using aromatic companions that release volatile compounds.[19]Other benefits, depending on the companion species used, include fi xing nitrogen, attracting beneficial insects, suppressing weeds, reducing root-damagingnematodeworms, and maintaining moisture in the soil.[19]

Some of the many mechanisms by whichpolycultureincluding companion planting may help to protect crops or otherwise increase productivity[19]

Nutrient provision[edit]

Root nodules of legumes fix nitrogen, assisting the growth of nearby plants.

Legumessuch ascloverprovide nitrogen compounds to neighbouring plants such as grasses byfi xing nitrogenfrom the air with symbiotic bacteria in theirroot nodules.These enable the grasses or other neighbours to produce more protein (with lower inputs of artificialfertiliser) and hence to grow more.[20][21][22][23]

Trap cropping[edit]

Further information:Trap crop

Trap croppinguses alternative plants to attract pests away from a main crop. For example,nasturtium(Tropaeolum majus) is a food plant of somecaterpillarswhich feed primarily on members of thecabbage family(brassicas);[24]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.[25]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.[26]

Host-finding disruption[edit]

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]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.[27]Companion planting ofcloveras ground cover was equally disruptive to eight pest species from four different insect orders. In a test, 36% ofcabbage root flieslaid 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.[27]

Weed suppression[edit]

Several plants areallelopathic,producing chemicals which inhibit the growth of other species. For example,ryeis useful as a cereal crop, and can be used as acover cropto suppress weeds in companion plantings, or mown and used as a weed-suppressingmulch.[28][29]Rye produces twophytotoxicsubstances, [2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA) and 2(3H)-benzoxazolinone (BOA)]. These inhibitgerminationand seedling growth of both grasses anddicotyledonousplants.[30]

Pest suppression[edit]

Companion planting ofcornflowersamongcabbageshelps theparasitoid waspMicroplitis mediator(shown) to controlcabbage moth.

Some companion plants help prevent pest insects or pathogenic fungi from damaging the crop, through their production of aromaticvolatile chemicals,another type of allelopathy.[17]For example, the smell of the foliage ofmarigoldsis claimed to deteraphidsfrom feeding on neighbouring plants.[31]A 2005 study found that oil volatiles extracted fromMexican marigoldcould suppress the reproduction of three aphid species (pea aphid,green peach aphidandglasshouse and potato aphid) by up to 100% after 5 days from exposure.[32]Another example familiar to gardeners is the interaction of onions and carrots with each other's pests: it is popularly believed that the onion smell puts offcarrot root fly,while the smell of carrots puts offonion fly.[19][1]

Some studies have demonstrated beneficial effects. For instance,cabbagecrops can be seriously damaged by thecabbage moth.It has a natural enemy, the parasitoid waspMicroplitismediator.Companion planting ofcornflowersamong cabbages enables the wasp to increase sufficiently in number to control the moth. This implies the possibility of natural control, with reduced use of insecticides, benefiting the farmer and local biodiversity.[33]In horticulture, marigolds provide good protection to tomato plants against thegreenhouse whitefly(an aphid), via the aromaticlimonenethat they produce.[34]Not all combinations of target and companion are effective; for instance, clover, a useful companion to many crop plants, does not maskBrassicacrops.[35]

However, effects on multi-species systems are complex and may not increase crop yields. Thus,French marigoldinhibitscodling moth,a serious pest whose larva destroys apples, but it also inhibits the moth's insect enemies, such as theparasitoid waspAscogaster quadridentata,anichneumonid.The result is that the companion planting fails to reduce damage to apples.[36]

Predator recruitment[edit]

Spearmintattracts themiridbugNesidiocoris tenuis,an activepredatorthat helps to suppress crop pests.[37]

Companion plants that produce copious nectar orpollenin a vegetable garden (insectary plants) may help encourage higher populations ofbeneficial insectsthat control pests.[38]

Some companion herbs that produce aromatic volatiles attract natural enemies, which can help to suppress pests.Mint,basil,and marigold all attract herbivorous insects' enemies, such as generalist predators. For instance,spearmintattracts themiridbugNesidiocoris tenuis,while basil attracts the green lacewingCeraeochrysacubana.[37]

The multiple interactions between the plant species, and between them, pest species, and the pests' natural enemies, are complex and not well understood. A 2019 field study in Brazil found that companion planting withparsleyamong a target crop ofcollard greenshelped to suppress aphid pests (Brevicoryne brassicae,Myzus persicae), even though it also cut down the numbers ofparasitoid wasps.Predatoryinsect species increased in numbers, and may have predated on the aphid-killing parasitoids, while the reduction in aphids may have been caused by the increased numbers of generalist predators.[39]

Protective shelter[edit]

Shade-grown coffeeplantation inCosta Rica.The red trees in the background provide shade; those in the foreground have been pruned to allow full exposure to the sun.

Some crops are grown under the protective shelter of different kinds of plant, whether aswind breaksor for shade. For example,shade-grown coffee,especiallyCoffea 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.[40]Suitable Asian trees includeErythrina subumbrans(tton tong or dadap),Gliricidia sepium(khae falang),Cassia siamea(khi lek),Melia azedarach(khao dao sang), andPaulownia tomentosa,a useful timber tree.[41]

Approaches[edit]

Companion planting approaches in use or being trialled include:

  • Square foot gardeningattempts 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.[42]
  • Forest gardening,where companion plants are intermingled to simulate an ecosystem, emulates the interaction of plants of up to seven different heights in awoodland.[43]

See also[edit]

References[edit]

  1. ^ab"Companion Planting Guide".Thompson & Morgan.Archivedfrom the original on 2 January 2018.Retrieved14 June2016.
  2. ^Smith, B. D. (9 May 1997)."The initial domestication ofCucurbita pepoin the Americas 10,000 years ago "(PDF).Science.276(5314): 932–934.doi:10.1126/science.276.5314.932.Archived fromthe original(PDF)on 28 July 2020.
  3. ^"Cucurbitaceae--Fruits for Peons, Pilgrims, and Pharaohs".University of California, Los Angeles.Archived fromthe originalon 16 October 2013.Retrieved2 September2013.
  4. ^Mount Pleasant, Jane(2006). "The science behind the Three Sisters mound system: An agronomic assessment of an indigenous agricultural system in the northeast". In Staller, John E.; Tykot, Robert H.; Benz, Bruce F. (eds.).Histories of Maize: Multidisciplinary Approaches to the Prehistory, Linguistics, Biogeography, Domestication, and Evolution of Maize.Amsterdam:Academic Press.pp. 529–537.ISBN978-1-5987-4496-5.
  5. ^Landon, Amanda J. (2008)."The 'How' of the Three Sisters: The Origins of Agriculture in Mesoamerica and the Human Niche".Nebraska Anthropologist.23:110–124.ISSN1555-4937.Archivedfrom the original on 29 August 2021.Retrieved30 August2021.
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  7. ^Willis, R. J. (2008). "Allelopathy in the Classical World – Greece and Rome".The History of Allelopathy.Dordrecht: Springer. pp. 15–37.doi:10.1007/978-1-4020-4093-1_2.ISBN978-1-4020-4092-4.
  8. ^Theophrastus,Enquiry into Plants,Book IV, XVI, 5
  9. ^abAliotta, Giovanni; Mallik, Azim U.; Pollio, Antonino (2008). "Historical Examples of Allelopathy and Ethnobotany from the Mediterranean Region".Allelopathy in Sustainable Agriculture and Forestry.New York: Springer New York. pp. 11–24.doi:10.1007/978-0-387-77337-7_1.ISBN978-0-387-77336-0.
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  26. ^Holden, Matthew H.; Ellner, Stephen P.; Lee, Doo-Hyung; Nyrop, Jan P.; Sanderson, John P. (1 June 2012)."Designing an effective trap cropping strategy: the effects of attraction, retention and plant spatial distribution".Journal of Applied Ecology.49(3): 715–722.doi:10.1111/j.1365-2664.2012.02137.x.
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  33. ^Balmer, Oliver; Pfiffner, Lukas; Schied, Johannes; Willareth, Martin; Leimgruber, Andrea; Luka, Henryk; Traugott, Michael (2 July 2013)."Noncrop flowering plants restore top‐down herbivore control in agricultural fields".Ecology and Evolution.3(8).Wiley:2634–2646.doi:10.1002/ece3.658.ISSN2045-7758.PMC3930038.PMID24567828.
  34. ^Conboy, Niall J. A.; McDaniel, Thomas; Ormerod, Adam; George, David; Gatehouse, Angharad M. R.; Wharton, Ellie; Donohoe, Paul; Curtis, Rhiannon; Tosh, Colin R. (1 March 2019)."Companion planting with French marigolds protects tomato plants from glasshouse whiteflies through the emission of airborne limonene".PLOS One.14(3): e0213071.doi:10.1371/journal.pone.0213071.ISSN1932-6203.PMC6396911.PMID30822326.
  35. ^Parker, Joyce E.; Snyder, William E.; Hamilton, George C.; Rodriguez-Saona, Cesar (2013). "Companion Planting and Insect Pest Control".Weed and Pest Control - Conventional and New Challenges.InTech. pp. 1–26.
  36. ^Laffon, Ludivine; Bischoff, Armin; Gautier, Hélène; Gilles, Florent; Gomez, Laurent; Lescourret, Françoise; Franck, Pierre (6 October 2022)."Conservation Biological Control of Codling Moth (Cydia pomonella): Effects of Two Aromatic Plants, Basil (Ocimum basilicum) and French Marigolds (Tagetes patula)".Insects.13(10): 908.doi:10.3390/insects13100908.ISSN2075-4450.PMID36292856.
  37. ^abRim, Hojun; Hattori, Sayaka; Arimura, Gen-ichiro (7 February 2020)."Mint companion plants enhance the attraction of the generalist predator Nesidiocoris tenuis according to its experiences of conspecific mint volatiles".Scientific Reports.10(1). Springer: 2078.doi:10.1038/s41598-020-58907-6.ISSN2045-2322.PMC7005881.PMID32034224.
  38. ^"Pacific Northwest Nursery IPM. Flowers, Sweets and a Nice Place to Stay: Courting Beneficials to Your Nursery".Oregon State University.Archivedfrom the original on 17 April 2014.Retrieved11 February2013.
  39. ^Saldanha, Alan V.; Gontijo, Lessando M.; Carvalho, Rayana M.R.; Vasconcelos, Cristina J.; Corrêa, Alberto S.; Gandra, Robert L.R. (2019). "Companion planting enhances pest suppression despite reducing parasitoid emergence".Basic and Applied Ecology.41.Elsevier:45–55.doi:10.1016/j.baae.2019.10.002.ISSN1439-1791.S2CID208585125.
  40. ^Rice, Robert (2010)."The Ecological Benefits of Shade-Grown Coffee: The Case for Going Bird Friendly".Smithsonian.Archivedfrom the original on 1 May 2019.Retrieved1 May2019.
  41. ^Winston, Edward; Op de Laak, Jacques; Marsh, Tony; Lempke, Herbert; Chapman, Keith."Arabica Coffee Manual for Lao-PDR: Chapter 3 Field Management & Planting Trees".Food and Agriculture Organization.Archivedfrom the original on 1 May 2019.Retrieved1 May2019.
  42. ^Bartholomew, Mel (2013).All New Square Foot Gardening(2nd ed.).Cool Springs Press.ISBN978-1591865483.
  43. ^McConnell, Douglas John (1992).The Forest-Garden Farms of Kandy, Sri Lanka.Food & Agriculture Org. p. 1.ISBN978-9251028988.Archivedfrom the original on 9 August 2021.Retrieved26 November2020..See alsoMcConnell, Douglas John (1973).The economic structure of Kandyan forest-garden farms.OCLC5776386.
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