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

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. The technique may allow farmers to reduce costly inputs of artificial fertilisers and pesticides
.

Traditional practice

History

Companion planting was practiced in various forms by the indigenous peoples of the Americas prior to the arrival of Europeans. These peoples domesticated squash 8,000 to 10,000 years ago,[2][3] then maize, then common beans, 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.[4][5][6]

Authors in classical Greece and Rome, around 2000 years ago, were aware that some plants were toxic (allelopathic) to other plants nearby.[7] Theophrastus reported that the bay tree and the cabbage plant enfeebled grapevines.[8][9] Pliny the Elder wrote that the "shade" of the walnut tree (Juglans regia) poisoned other plants.[10][9]

In China, mosquito ferns (Azolla spp.) have been used for at least a thousand years as companion plants for rice 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.[11]

20th century

Further information: List of companion plants

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.[12] Permaculture advocates similar methods.[13]

The

controlled experiments to 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 including

herbivorous pests, 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]

multitrophic approach necessary.[16]

Mechanisms

Companion planting can help to increase

weed suppression, and pest control, including by providing habitat for beneficial 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 sacrificial trap 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 fixing nitrogen, attracting beneficial insects, suppressing weeds, reducing root-damaging nematode worms, and maintaining moisture in the soil.[19]

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

Nutrient provision

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

fixing nitrogen from the air with symbiotic bacteria in their root nodules. These enable the grasses or other neighbours to produce more protein (with lower inputs of artificial fertiliser) and hence to grow more.[20][21][22][23]

Trap cropping

Further information: Trap crop

nasturtium (Tropaeolum majus) is a food plant of some caterpillars which feed primarily on members of the cabbage 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

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 of clover 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.[27]

Weed suppression

Several plants are allelopathic, producing chemicals which inhibit the growth of other species. For example, rye is useful as a cereal crop, and can be used as a cover crop to suppress weeds in companion plantings, or mown and used as a weed-suppressing mulch.[28][29] Rye produces two phytotoxic substances, [2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA) and 2(3H)-benzoxazolinone (BOA)]. These inhibit germination and seedling growth of both grasses and dicotyledonous plants.[30]

Pest suppression

Companion planting of cornflowers among cabbages helps the parasitoid wasp Microplitis mediator (shown) to control cabbage moth.

Some companion plants help prevent pest insects or pathogenic fungi from damaging the crop, through their production of aromatic

onion fly.[19][1]

Some studies have demonstrated beneficial effects. For instance, cabbage crops can be seriously damaged by the cabbage moth. It has a natural enemy, the parasitoid wasp Microplitis mediator. Companion planting of cornflowers among 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 the greenhouse whitefly (an aphid), via the aromatic limonene that they produce.[34] Not all combinations of target and companion are effective; for instance, clover, a useful companion to many crop plants, does not mask Brassica crops.[35]

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

Predator recruitment

Spearmint attracts the mirid bug Nesidiocoris tenuis, an active predator that helps to suppress crop pests.[37]

Companion plants that produce copious nectar or

insectary plants) may help encourage higher populations of beneficial insects that 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, spearmint attracts the mirid bug Nesidiocoris tenuis, while basil attracts the green lacewing Ceraeochrysa cubana.[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 with

collard greens helped to suppress aphid pests (Brevicoryne brassicae, Myzus persicae), even though it also cut down the numbers of parasitoid wasps. Predatory insect 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

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.

Some crops are grown under the protective shelter of different kinds of plant, whether as

Cassia siamea (khi lek), Melia azedarach (khao dao sang), and Paulownia tomentosa, a useful timber tree.[41]

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.[42]
  • 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.[43]

See also

References

  1. ^
    Thompson & Morgan. Archived
    from the original on 2 January 2018. Retrieved 14 June 2016.
  2. doi:10.1126/science.276.5314.932. Archived from the original
    (PDF) on 28 July 2020.
  3. ^ "Cucurbitaceae--Fruits for Peons, Pilgrims, and Pharaohs". University of California, Los Angeles. Archived from the original on 16 October 2013. Retrieved 2 September 2013.
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  8. Enquiry into Plants
    , Book IV, XVI, 5
  9. ^
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    .
  10. ^ Pliny the Elder, Natural History, Book XVII: 89
  11. ^ "Plant Resources for Human Development-Nitrogen in Rice" (PDF). Dhakai.com. p. 5. Archived from the original (PDF) on 4 March 2016. Retrieved 21 February 2015.
  12. ^ "5 Secrets to Vegetable Garden, Companion Planting Revealed". Organic Authority. 22 October 2018. Archived from the original on 1 May 2019. Retrieved 1 May 2019.
  13. ^ Ludwig-Cooper, Stephanie (2 December 2011). "Companion Planting Information and Chart". Permaculture News. Retrieved 18 October 2023.
  14. ^ "Companion Plants". Alabama Cooperative Extension System. Archived from the original on 30 April 2015. Retrieved 3 January 2021.
  15. ^ Riesselman, Leah. Companion planting: A method for sustainable pest control (PDF) (Technical report). Iowa State University. RFR-A9099. Archived from the original (PDF) on 14 May 2013. Retrieved 22 March 2014.
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  20. ^ Wagner, S. C. (2011). "Biological Nitrogen Fixation". Nature Education Knowledge. 3 (10): 15. Archived from the original on 13 September 2018. Retrieved 1 May 2019.
  21. PMID 28607058
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  22. ^ Postgate, J. (1998). Nitrogen Fixation. Cambridge University Press. Chapter 1: The nitrogen cycle; Chapter 3: Physiology; Chapter 4: The free-living microbes.
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  24. ^ "Cabbage caterpillars". Royal Horticultural Society. Archived from the original on 25 February 2013. Retrieved 10 February 2013.
  25. ^ Pleasant, Barbara (June–July 2011). "Organic Pest Control: What Works, What Doesn't". Mother Earth News (246): 36–41.
  26. doi:10.1111/j.1365-2664.2012.02137.x
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  27. ^ a b c Finch, S.; Collier, R. H. (2003). "Insects can see clearly now the weeds have gone" (PDF). Biologist. 50 (3): 132–135. Archived (PDF) from the original on 1 August 2020. Retrieved 15 September 2011.
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  31. ^ Pleasant, Barbara (22 January 2013). "Attract Hoverflies for Organic Aphid Control". Mother Earth News. Archived from the original on 1 August 2020. Retrieved 3 January 2022.
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  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.
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  38. ^ "Pacific Northwest Nursery IPM. Flowers, Sweets and a Nice Place to Stay: Courting Beneficials to Your Nursery". Oregon State University. Archived from the original on 17 April 2014. Retrieved 11 February 2013.
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  40. ^ Rice, Robert (2010). "The Ecological Benefits of Shade-Grown Coffee: The Case for Going Bird Friendly". Smithsonian. Archived from the original on 1 May 2019. Retrieved 1 May 2019.
  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. Archived from the original on 1 May 2019. Retrieved 1 May 2019.
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