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. KarottenZwiebeln 266.JPG
Companion planting of carrots and onions. The onion smell puts off carrot root fly, while the smell of carrots puts off onion fly.

Companion planting in gardening and agriculture is the planting of different crops in proximity for any of a number of different reasons, including weed suppression, pest control, pollination, providing habitat for beneficial insects, maximizing use of space, and to otherwise increase crop productivity. Companion planting is a form of polyculture.

Contents

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

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 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 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 from 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 plant disease resistance in crops, conservation of natural enemies (parasitoids and predators) to provide biological pest control, and companion planting such as with aromatic forbs to repel pests should be used to achieve "sustainable" protection of crops. They considered a multitrophic approach that took into account the many interactions between crops, companion plants, 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]

Multiple interactions between companion plants, target crops, weeds, pests, and beneficial insects such as parasitoids and predators of the pests make a multitrophic approach necessary. Companion Planting Interactions.svg
Multiple interactions between companion plants, target crops, weeds, pests, and beneficial insects such as parasitoids and predators of the pests make a multitrophic approach necessary.

Mechanisms

Companion planting can help to increase crop productivity through a variety of mechanisms, which may sometimes be combined. These include pollination, 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 Companion Planting Mechanisms.svg
Some of the many mechanisms by which polyculture including companion planting may help to protect crops or otherwise increase productivity

Nutrient provision

Root nodules of legumes fix nitrogen, assisting the growth of nearby plants. Medicago sativa root nodules.JPG
Root nodules of legumes fix nitrogen, assisting the growth of nearby plants.

Legumes such as clover 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 (with lower inputs of artificial fertiliser) and hence to grow more. [20] [21] [22] [23]

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 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. Microplitis mediator adult female.jpg
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 volatile chemicals, another type of allelopathy. [17] For example, the smell of the foliage of marigolds is claimed to deter aphids from feeding on neighbouring plants. [31] A 2005 study found that oil volatiles extracted from Mexican marigold could suppress 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. [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 off carrot root fly, while the smell of carrots puts off 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. Nesiocoris tenuis on leaf.jpg
Spearmint attracts the mirid bug Nesidiocoris tenuis, an active predator that helps to suppress crop pests.

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. [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 parsley among a target crop of 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. Coffee shadow trees costa rica.jpg
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. [40] 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. [41]

Approaches

Companion planting approaches in use or being trialled include:

See also

Related Research Articles

<span class="mw-page-title-main">Crop rotation</span> Agricultural practice of changing crops

Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. This practice reduces the reliance of crops on one set of nutrients, pest and weed pressure, along with the probability of developing resistant pests and weeds.

<span class="mw-page-title-main">Biological pest control</span> Controlling pests using other organisms

Biological control or biocontrol is a method of controlling pests, whether pest animals such as insects and mites, weeds, or pathogens affecting animals or plants by using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also involves an active human management role. It can be an important component of integrated pest management (IPM) programs.

<span class="mw-page-title-main">Aphid</span> Superfamily of insects

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 typical life cycle involves flightless females giving live birth to female nymphs—who may also be already pregnant, an adaptation scientists call telescoping generations—without the involvement of males. Maturing rapidly, females breed profusely so that the number of these insects multiplies quickly. Winged females may develop later in the season, allowing the insects to colonize new plants. In temperate regions, a phase of sexual reproduction occurs in the autumn, with the insects often overwintering as eggs.

<span class="mw-page-title-main">Whitefly</span> Family of insects

Whiteflies are Hemipterans that typically feed on the undersides of plant leaves. They comprise the family Aleyrodidae, the only family in the superfamily Aleyrodoidea. More than 1550 species have been described.

<span class="mw-page-title-main">Intercropping</span> Multiple cropping practice involving growing two or more crops in proximity

Intercropping is a multiple cropping practice that involves the cultivation of two or more crops simultaneously on the same field, a form of polyculture. The most common goal of intercropping is to produce a greater yield on a given piece of land by making use of resources or ecological processes that would otherwise not be utilized by a single crop.

<span class="mw-page-title-main">Cover crop</span> Crop planted to manage erosion and soil quality

In agriculture, cover crops are plants that are planted to cover the soil rather than for the purpose of being harvested. Cover crops manage soil erosion, soil fertility, soil quality, water, weeds, pests, diseases, biodiversity and wildlife in an agroecosystem—an ecological system managed and shaped by humans. Cover crops can increase microbial activity in the soil, which has a positive effect on nitrogen availability, nitrogen uptake in target crops, and crop yields. Cover crops may be an off-season crop planted after harvesting the cash crop. Cover crops are nurse crops in that they increase the survival of the main crop being harvested, and are often grown over the winter. In the United States, cover cropping may cost as much as $35 per acre.

<span class="mw-page-title-main">Beneficial insect</span>

Beneficial insects 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 outcomes from a human perspective. In agriculture, where the goal is to raise selected crops, insects that hinder the production process are classified as pests, while insects that assist production are considered beneficial. In horticulture and gardening, beneficial insects are often considered those that contribute to pest control and native habitat integration.

<span class="mw-page-title-main">Polyculture</span> Growing multiple crops together in agriculture

In agriculture, polyculture is the practice of growing more than one crop species together, in contrast to monoculture, which had become the dominant approach in the 20th century. Traditional examples include the intercropping of the three sisters, namely maize, beans, and squash, by indigenous peoples of Central and North America, and the rice-fish systems of Asia. Polyculture serves multiple functions in the ecology of agriculture, including controlling insect pests, plant diseases, and weeds. Polyculture can contribute to sustainable agriculture as unlike monoculture it does not rely on pesticides, requires less tillage, increases local biodiversity, and where legumes are involved, help to maintain soil nitrogen.

<span class="mw-page-title-main">Allelopathy</span> Production of biochemicals which affect the growth of other organisms

Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial or detrimental effects on the target organisms and the community. Allelopathy is often used narrowly to describe chemically-mediated competition between plants; however, it is sometimes defined more broadly as chemically-mediated competition between any type of organisms. Allelochemicals are a subset of secondary metabolites, which are not directly required for metabolism of the allelopathic organism.

<span class="mw-page-title-main">Living mulch</span> Cover crop grown with a main crop as mulch

In agriculture, a living mulch is a cover crop interplanted or undersown with a main crop, and intended to serve the purposes of a mulch, such as weed suppression and regulation of soil temperature. Living mulches grow for a long time with the main crops, whereas cover crops are incorporated into the soil or killed with herbicides.

In agriculture and gardening, a beneficial organism is any organism that benefits the growing process, including insects, arachnids, other animals, plants, bacteria, fungi, viruses, and nematodes. Benefits include pest control, pollination, and maintenance of soil health. The opposite of beneficial organisms are pests, which are organisms deemed detrimental to the growing process. There are many different types of beneficial organisms as well as beneficial microorganisms. Also, microorganisms have things like salt and sugar in them. Beneficial organisms include but are not limited to: Birds, Bears, Nematodes, Insects, Arachnids, and fungi. The ways that birds and bears are considered beneficial is mainly because they consume seeds from plant and spread them through feces. Birds also prey on certain insects that eat plants and hinder them from growing these insects are known as non beneficial organisms. Nematodes are considered beneficial because they will help compost and provide nutrients for the soil the plants are growing in. Insects and arachnids help the growing process because they prey on non beneficial organisms that consume plants for food. Fungi help the growing process by using long threads of mycelium that can reach very long distances away from the tree or plant and bring water and nutrients back to the tree or plant roots.

<span class="mw-page-title-main">Push–pull agricultural pest management</span> Intercropping strategy for controlling agricultural pests

Push–pull technology is an intercropping strategy for controlling agricultural pests by using repellent "push" plants and trap "pull" plants. For example, cereal crops like maize or sorghum are often infested by stem borers. Grasses planted around the perimeter of the crop attract and trap the pests, whereas other plants, like Desmodium, planted between the rows of maize, repel the pests and control the parasitic plant Striga. Push–pull technology was developed at the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya in collaboration with Rothamsted Research, UK. and national partners. This technology has been taught to smallholder farmers through collaborations with universities, NGOs and national research organizations.

<span class="mw-page-title-main">Beneficial weed</span> Invasive plant with positive effects

A beneficial weed is an invasive plant that has some companion plant effect, is edible, contributes to soil health, adds ornamental value, or is otherwise beneficial. These plants are normally not domesticated. However, some invasive plants, such as dandelions, are commercially cultivated, in addition to growing in the wild. Beneficial weeds include many wildflowers, as well as other weeds that are commonly removed or poisoned. Certain weeds that have obnoxious and destructive qualities have been shown to fight illness and are thus used in medicine. For example, Parthenium hysterophorus native to northern Mexico and parts of the US has been an issue for years due to its toxicity and ability to spread rapidly. In the past few decades, though, research has found that P. hysterophorus was "used in traditional medicine to treat inflammation, pain, fever, and diseases like malaria dysentery." It is also known to create biogas that can be used as a bioremediation agent to break down heavy metals and other pollutants.

A trap crop is a plant that attracts agricultural pests, usually insects, away from nearby target crops. This form of companion planting can save a target crop from decimation by pests without the use of artificial pesticides. A trap crop is used for attracting the insect and pests away from a target crop field. Many trap crops have successfully diverted pests from focal crops in small scale greenhouse, garden and field experiments; a small portion of these plants have been shown to reduce pest damage at larger commercial scales. A common explanation for reported trap cropping failures, is that attractive trap plants only protect nearby plants if the insects do not move back into the target crop. In a review of 100 trap cropping examples in 2006, only 10 trap crops were classified as successful at a commercial scale, and in all successful cases, trap cropping was supplemented with management practices that specifically limited insect dispersal from the trap crop back into the target crop.

<span class="mw-page-title-main">Weed</span> Plant considered undesirable in a particular place or situation

A weed is a plant considered undesirable in a particular situation, growing where it conflicts with human preferences, needs, or goals. Plants with characteristics that make them hazardous, aesthetically unappealing, difficult to control in managed environments, or otherwise unwanted in farm land, orchards, gardens, lawns, parks, recreational spaces, residential and industrial areas, may all be considered weeds. The concept of weeds is particularly significant in agriculture, where the presence of weeds in fields used to grow crops may cause major losses in yields. Invasive species, plants introduced to an environment where their presence negatively impacts the overall functioning and biodiversity of the ecosystem, may also sometimes be considered weeds.

<i>Chloridea virescens</i> Species of moth

Chloridea virescens, commonly known as the tobacco budworm, is a moth of the family Noctuidae found throughout the eastern and southwestern United States along with parts of Central America and South America.

<i>Macrosiphum euphorbiae</i> Species of true bug

Macrosiphum euphorbiae, the potato aphid, is a sap-sucking pest insect in the family Aphididae. It infests potatoes and a number of other commercially important crops.

<span class="mw-page-title-main">Tritrophic interactions in plant defense</span> Ecological interactions

Tritrophic interactions in plant defense against herbivory describe the ecological impacts of three trophic levels on each other: the plant, the herbivore, and its natural enemies. They may also be called multitrophic interactions when further trophic levels, such as soil microbes, endophytes, or hyperparasitoids are considered. Tritrophic interactions join pollination and seed dispersal as vital biological functions which plants perform via cooperation with animals.

References

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  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 . ISSN   2075-4450. PMID   36292856.
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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.
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  42. ↑ Bartholomew, Mel (2013). All New Square Foot Gardening (2nd ed.). Cool Springs Press. ISBN   978-1591865483.
  43. ↑ McConnell, Douglas John (1992). The Forest-Garden Farms of Kandy, Sri Lanka. Food & Agriculture Org. p. 1. ISBN   978-9251028988. Archived from the original on 9 August 2021. Retrieved 26 November 2020.. See also McConnell, Douglas John (1973). The economic structure of Kandyan forest-garden farms. OCLC   5776386.
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