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These include:
1) Building fertility:
- Weeds are the best source of mulch and compost material.
- Deep rooting weeds like docks, dandelions, thistles and plantains bring up nutrients from deep in the soil that can be put back into the topsoil by cutting them for mulch material or composting.
- Making liquid plant feeds, particularly nettles, also dandelion leaves.
- Roots break up and aerate the soil.
- Roots hold the soil in place preventing erosion.
- Cover bare soil. This helps control soil moisture and temperature and prevents the compaction of the ground and the washing out of soluble nutrients (leaching).
2) Deterring pests:
- Flowers of native plants attract beneficial insects that are predators of crop eating pests.
- Cover provided offers habitats for beneficial insects.
- Confuse and distract insects and other pests from crops.
- Act as a sacrificial crop by getting eaten instead of wanted plants.
3) Providing for wildlife:
- Cover for birds, insects, frogs etc.
- Flowers attract bees and other pollinating insects. Many of the flowers bred and grown as ornamentals have flower shapes that do not allow native bees, butterflies and moths to reach the nectar.
- Native plants provide important food sources for native wildlife. For example the larvae of native butterflies only feed on a few native plants specific to each species, these include some common garden weeds like thistles.
4) Helping to alleviate pollution:
- Take up carbon dioxide and produce oxygen- the more greenery the better.
- Absorb soil and air pollutants
5) Showing the presence of certain nutrients in the soil:
These are known as indicator species
USES OF SOME COMMON WEEDS
Dandelion, Taraxacum officinale
Attracts pollinating insects especially bees. An important food plant for native caterpillars and moths of many species. Leaves excellent for liquid feed, mulch material and on the compost pile because they contain high levels of potassium salts. Long tap-root up to 1 metre brings up nutrients from low in the soil. The flowers can be used to make wine.
Clovers, Trifolium species
Clover flowers are an important nectar source for native bees, moths and butterflies. The decrease of the meadow habitat of red clover Trifolium pratense has been linked to the demise of native bee populations. They are excellent for ground cover and mixing with other plants that benefit from the clovers ability to fix atmospheric nitrogen.
Nettles, Urtica dioica
A very useful plant. Nutrient rich leaves make excellent liquid feed, compost activator and mulch material that breaks down very quickly. Young leaves cooked make a good substitute for spinach, very nutritious and easily digested. Is an indicator of good fertile soil rich in nitrogen and phosphates. Tea made from fresh leaves helps relieve hay fever in many sufferers.
Yarrow, Achillea millefolium
Repels insect pests and so makes a good companion plant. Useful as a liquid feed, compost and mulch ingredient. Is very tolerant of cutting and trampling. Growing widely it is an indicator of low soil potassium, a nutrient particularly important for fruit and flower formation. Correct this by adding compost, cut comfrey, urine, wood ash and seaweed meal. Dried plant said to make effective mosquito repellent
Fat hen, Chenopodium album
A common weed of cultivated ground that is also a tasty vegetable used like spinach.
Tansy, Tanacetum vulgare
A good companion plant in the garden, the flowers are very attractive hoverflies and both growing and dried plant repels flies, fleas, lice and ants. Particularly good around fruit trees where it helps deter pests.
Coltsfoot, Tussilago farfara
Has a very extensive root system, a good accumulator of nutrients. Leaves make useful mulch and compost material. Young leaves and flowers are acceptable in mixed salads with an anisseedy flavour. Is a popular herbal remedy for coughs and chest complaints.
NB.
There are a few real problem weeds that once established, can swamp everything else including native vegetation. These are mostly non-native perennial plants that spread vigourously at the roots. For example, Japanese Knotweed was introduced in Britain as a garden ornamental by the Victorians and is now next to impossible to eradicate.
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