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 pest control, pollination, providing habitat for beneficial insects, maximizing use of space, and to otherwise increase crop productivity.[2] 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 cottage gardens in England and forest gardens in Asia, and thousands of years ago in Mesoamerica.


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 that fixes nitrogen from the atmosphere, and they block light from plants that would compete with the rice.[3]

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,[4][5] 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.[6][7][8]

Companion planting was widely promoted in the 1970s as part of the organic gardening movement.[9] It was encouraged for pragmatic reasons, such as natural trellising, but mainly with the idea that different species of plant may thrive more when close together.[10] It is also a technique frequently used in permaculture, together with mulching, polyculture, and changing of crops.[11]


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

Provision of nutrients[edit]

Legumes such as clover provide nitrogen compounds to other plants such as grasses by fixing nitrogen from the air with symbiotic bacteria in their root nodules.[12][13][14][15]

Dandelions have long taproots that bring nutrients from deep within the soil to near the surface, benefitting neighboring plants that are shallower-rooted.[16]

Trap cropping[edit]

Trap cropping uses alternative plants to attract pests away from a main crop. For example, nasturtium (Tropaeolum majus) is a food plant of some caterpillars which feed primarily on members of the cabbage family (brassicas);[17] 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.[18] However, while many trap crops have successfully diverted pests off of focal crops in small scale greenhouse, garden and field experiments, only a small portion of these plants have been shown to reduce pest damage at larger commercial scales.[19]

Host-finding disruption[edit]

Recent studies on host-plant finding have shown that flying pests are far less successful if their host-plants are surrounded by any other plant or even "decoy-plants" made of green plastic, cardboard, or any other green material.[20]

The host-plant finding process occurs in phases:[20]

  • The first phase is stimulation by odours characteristic to the host-plant. This induces the insect to try to land on the plant it seeks. But insects avoid landing on brown (bare) soil. So if only the host-plant is present, the insects will quasi-systematically find it by simply landing on the only green thing around. This is called (from the point of view of the insect) "appropriate landing". When it does an "inappropriate landing", it flies off to any other nearby patch of green. It eventually leaves the area if there are too many 'inappropriate' landings.[20]
  • The second phase of host-plant finding is for the insect to make short flights from leaf to leaf to assess the plant's overall suitability. The number of leaf-to-leaf flights varies according to the insect species and to the host-plant stimulus received from each leaf. The insect must accumulate sufficient stimuli from the host-plant to lay eggs; so it must make a certain number of consecutive 'appropriate' landings. Hence if it makes an 'inappropriate landing', the assessment of that plant is negative, and the insect must start the process anew.[20]

Thus it was shown that clover used as a ground cover had the same disruptive effect on eight pest species from four different insect orders. An experiment showed that 36% of cabbage root flies laid eggs beside cabbages growing in bare soil (which resulted in no crop), compared to only 7% beside cabbages growing in clover (which allowed a good crop). Simple decoys made of green cardboard also disrupted appropriate landings just as well as did the live ground cover.[20]

Pest suppression[edit]

Some companion plants help prevent pest insects or pathogenic fungi from damaging the crop, through chemical means.[21] For example, the smell of the foliage of marigolds is claimed to deter aphids from feeding on neighbouring plants.[22] 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.[23]

Predator recruitment[edit]

Companion plants that produce copious nectar or pollen in a vegetable garden (insectary plants) may help encourage higher populations of beneficial insects that control pests,[24] as some beneficial predatory insects only consume pests in their larval form and are nectar or pollen feeders in their adult form. For instance, marigolds with simple flowers attract nectar-feeding adult hoverflies, the larvae of which are predators of aphids.[22]

Protective shelter[edit]

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 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.[25] 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.[26]


Systems in use or being trialled include:

Square foot gardening attempts to protect plants from many normal gardening problems, such as weed infestation, by packing them as closely together as possible, which is facilitated by using companion plants, which can be closer together than normal.[27]

Forest gardening, where companion plants are intermingled to create an actual ecosystem, emulates the interaction of up to seven levels of plants in a forest or woodland.[28][29]

Organic gardening makes frequent use of companion planting, since many other means of fertilizing, weed reduction and pest control are forbidden.[30]

See also[edit]


  1. ^ "Companion Planting Guide". Thompson & Morgan. Retrieved 14 June 2016.
  2. ^ McClure, Susan (1994). Companion Planting. Rodale Press. ISBN 978-0-87596-616-8.
  3. ^ "Plant Resources for Human Development-Nitrogen in Rice" (PDF). Archived from the original (PDF) on March 4, 2016. Retrieved February 21, 2015.
  4. ^ Smith, B. D. (1997). The initial domestication of Cucurbita pepo in the Americas 10,000 years ago. Science 276 932-34.
  5. ^ "Cucurbitaceae--Fruits for Peons, Pilgrims, and Pharaohs". University of California at Los Angeles. Archived from the original on October 16, 2013. Retrieved September 2, 2013.
  6. ^ 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. ISBN 978-1-5987-4496-5.
  7. ^ 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. ISSN 1555-4937.
  8. ^ Bushnell, G. H. S. (1976). "The Beginning and Growth of Agriculture in Mexico". Philosophical Transactions of the Royal Society of London. 275 (936): 117–120. doi:10.1098/rstb.1976.0074.
  9. ^ "Companion Planting Guide". Mel's Garden. 2018-07-11. Retrieved 12 July 2018.
  10. ^ "7 Reasons For Companion Planting". Garden & Greenhouse. Retrieved 12 July 2018.
  11. ^ "Companion Planting Guide". Mel's Garden. 2018-07-11. Retrieved 12 July 2018.
  12. ^ Wagner, S. C. (2011). "Biological Nitrogen Fixation". Nature Education Knowledge. 3 (10): 15.
  13. ^ Wang, Qi & Yang, Shengming (2017). "Host-secreted antimicrobial peptide enforces symbiotic selectivity in Medicago truncatula". PNAS. 114 (26): 6854–6859. doi:10.1073/pnas.1700715114. PMC 5495241. PMID 28607058.
  14. ^ Postgate, J. (1998). Nitrogen Fixation. Cambridge University Press.
  15. ^ Smil, V. (2000). Cycles of Life. Scientific American Library.
  16. ^ Anon. "Companion Planting for Vegetables & Plants". Country living and farm lifestyles. Retrieved 2011-03-07.
  17. ^ "Cabbage caterpillars". Royal Horticultural Society. Retrieved 10 February 2013.
  18. ^ Pleasant, Barbara (June–July 2011). "ORGANIC PEST CONTROL WHAT WORKS, WHAT DOESN'T". Mother Earth News (246): 36–41.
  19. ^ Holden, Matthew H.; Ellner, Stephen P.; Lee, Doo-Hyung; Nyrop, Jan P.; Sanderson, John P. (2012-06-01). "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.
  20. ^ a b c d e Horticulture Research International, Wellesbourne : "Insects can see clearly now the weeds have gone". Finch, S. & Collier, R. H. (2003). Biologist, 50 (3), 132-135
  21. ^ "The Self-Sufficient Gardener Podcast--Episode 24 Companion Planting and Crop Rotation". Retrieved 2010-08-13.
  22. ^ a b "Attract Hoverflies for Organic Aphid Control".
  23. ^ Tomova, Blagovesta S.; Waterhouse, John S.; Doberski, Julian (2005). "The effect of fractionated Tagetes oil volatiles on aphid reproduction". Entomologia Experimentalis et Applicata. 115 (1): 153–159. doi:10.1111/j.1570-7458.2005.00291.x. ISSN 1570-7458. S2CID 86565848.
  24. ^ "Pacific Northwest Nursery IPM. Flowers, Sweets and a Nice Place to Stay: Courting Beneficials to Your Nursery". Oregon State University. Retrieved 11 February 2013.
  25. ^ Rice, Robert (2010). "The Ecological Benefits of Shade-Grown Coffee: The Case for Going Bird Friendly". Smithsonian.
  26. ^ Winston, Edward; Jacques Op de Laak; Tony Marsh; Herbert Lempke & Keith Chapman. "Arabica coffee manual for Lao-PDR |Chapter 3 Field management & planting trees". Food and Agriculture Organization. Retrieved 1 May 2019.
  27. ^ Bartholomew, Mel (2013). All New Square Foot Gardening (2nd ed.). Cool Springs Press. ISBN 978-1591865483.
  28. ^ Douglas John McConnell (1992). The Forest-Garden Farms of Kandy, Sri Lanka. p. 1. ISBN 9789251028988.
  29. ^ McConnell, Douglas John (1973). The economic structure of Kandyan forest-garden farms.
  30. ^ "5 Secrets to Vegetable Garden, Companion Planting Revealed". Organic Authority. 22 October 2018. Retrieved 1 May 2019.

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