]] A beneficial weed can be an invasive plant that has some companion plant effect, which is edible, contributes to soil health, adds ornamental value,
Soil health
Beneficial weeds are erroneously considered to compete with neighboring plants for food and moisture. However, some "weeds" provide the soil with nutrients, either directly or indirectly.
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For example, if they are colonized by certain bacteria (most commonly Rhizobium), legumes such as white clover add nitrogen to the soil through the process of nitrogen fixation.
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Others use deep to bring up nutrients and moisture from beyond the range of normal plants so that the soil improves in quality over generations of that plant's presence. Root-derived soil which is retained more stable soil aggregates than shoot-derived soil. Although roots normally contribute in generally 20% of the total plant weight, which is well-developed root system also essential for healthy plant growth and development.
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Weeds with strong, widespread roots also introduce organic matter to the soil in the form of those roots, turning hard, dense clay dirt into richer, more Soil fertility.
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Some plants like and maize will piggyback on nearby weeds, allowing their relatively weak root systems to grow deeper.
Pest prevention
Many weeds protect nearby plants from
. Some beneficial weeds release volatile organic compounds that mask the scents of nearby plants, as with
and wormwood; others imitate the
of pest insects and confuse them, as with
ground ivy,
oregano, and other
Mentha. In addition, a number of beneficial weeds have spines or other features that deter pest insects.
Trap crops
Some weeds act as
, distracting pests away from valued plants. Insects often search for target plants by smell, and then land at random on anything green in the area of the scent. If they land on an edible "weed", they will stay there instead of going on to the intended victim. Sometimes, they actively prefer the trap crop.
Host-finding disruption
The use of certain weeds integrated around native or otherwise intended plants has been found to be beneficial in many ways. A 2015 study showed that the presence of other plants or decoy plants made of green plastic, cardboard, or any other green materials can significantly reduce the success rate of flying pests in locating their host plants.
These pests:
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Locate plants primarily by Odor, and any "weed" that has a strong scent can mask the scent of the host plant and reduce the odds of the pest finding it. Examples of such plants include Allium vineale and Ground Ivy, which have been found to effectively reduce infestations of and , respectively.
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Tend to avoid landing on bare earth and instead opt for the nearest green surface. Using "green mulch" or other types of greenery can also make it more difficult for pests to locate their target by making "inappropriate landings" on other plants.
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Have difficulty laying eggs on a crop in the presence of other greenery, for example flies take 2-5 times longer if they land on a non-host disruptor plant.
Some "weed" species, such as subterranean clover (
Trifolium subterraneum L.), have been found to be specifically beneficial against pests targeting crops of common cabbage (
Brassica) species, reducing insects by 39%-100% on brassica plants when they were sown surrounded with clover as compared to when surrounded by bare soil.
The differences in the colonization of such insects appear sufficient to determine the lower numbers of insects found that where when host plants are surrounded and under sown with clover.
Companion plants
Many plants can grow
in the same space because they exist on different levels in the same area, providing ground cover or working as a trellis for each other.
This healthier style of
horticulture is called
forest gardening. Larger plants provide a wind break or shelter from the noonday sun for more delicate plants.
Green mulch
Conversely, some intercropped plants provide a
living mulch effect, able to inhibit the growth of harmful weeds and create a humid, cooler microclimate around nearby plants to stabilize soil moisture.
Plants such as ryegrass, red clover, and white clover are examples of "weeds" that are living mulches, often welcomed in horticulture.
Herbicide
Plants or
fungus can be repelled through a chemical means known as
allelopathy.
Certain plants can be affected by a chemical emission through their roots or air, slowing their growth, preventing
seed germination, or even killing them.
Beneficial insects
A common companion plant benefit from many weeds is to attract and provide habitat for beneficial insects or other organisms that benefit plants.
For example, wild attract predatory and flies. The adults eat nectar, but they feed common garden pests to their offspring.
Some weeds attract Coccinellidae or "good" types of , or provide ground cover for predatory beetles.
Uses for humans
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Some beneficial weeds, such as Chenopodium and purslane, are edible and highly nutritional. , a widespread invasive weed, were introduced to North America originally because they were considered a staple source of food; they were admired for maturing quickly and spreading vastly.
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A number of weeds have been proposed as natural alternate sources for latex (rubber), including goldenrod, from which the tires were made on the car famously given by Henry Ford to Thomas Edison.
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Cocklebur and stinging nettle have been used for and medicinal purposes.
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Some plants seem to subtly improve the flavor of other plants around them. For example, Urtica dioica, besides being edible if properly cooked, seems to increase essential oil production in nearby herbs.
Examples
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Clover, like other , hosts bacteria that fix nitrogen in the soil. Its vining nature covers the ground, sheltering more moisture than it consumes, providing a humid, cooler microclimate for surrounding plants as a "green mulch". It also is preferred by rodents over many garden crops, reducing the loss of vegetable crops.
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Dandelions possess a deep, strong tap root that breaks up hard soil, benefiting weaker-rooted plants nearby and drawing up nutrients from deeper than shallower-rooted nearby plants can access. They will also excrete minerals and nitrogen through their roots,
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Crow garlic, the wild chives found in sunny parts of a North American yard, has all of the companion plant benefits of other , including repelling japanese beetles, aphids, and rodents, and is believed to benefit the flavor of like tomatoes and peppers. It can be used as a substitute for garlic in cooking, though it may lend a bitter aftertaste.
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Daucus carota works as a nurse plant for nearby crops like lettuce, shading them from overly intense sunlight and keeping more humidity in the air. It attracts predatory wasps and flies that eat vegetable pests. It has a scientifically tested
See also
Further reading
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Schoonhoven, L.M., J. J. A van Loon, and Marcel Dicke. 2005. Insect-plant biology. Oxford University Press, London.
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Cover Crops - Living Mulches
External links
