Urtica dioica L.
Perennial Broad-leaved Weeds
A rhizomatous to stoloniferous perennial, common nettle is abundant and generally distributed in the UK and is recorded up to 2,700 ft. It is native on riverbanks and in hedgerows, grassy places, near buildings and where the ground is littered with rubble. Common nettle is favoured by conditions in woodland clearings and at the early stages of coppicing. It likes high nitrogen levels and can survive in moderate shade. The rhizomes have difficulty penetrating compacted soil and it prefers open textured soils of pH 5.0 to 8.0.
As a perennial weed, common nettle is troublesome around the margins of arable fields and in gardens. It is also prolific on the rich land that borders meadows and pastures, often encroaching into the field. However, it does not spread far into arable fields except as isolated seedlings. In a study of seedbanks in arable soils in the English midlands sampled in 1972-3, common nettle seed was recorded in 13% of the fields sampled in Oxfordshire and 41% of those in Warwickshire but never in large numbers.
Common nettle is variable in size, leaf shape and flower form, and several varieties have been described.
Dried nettles provide excellent fodder and are readily eaten by farm animals. If cut before flowering and thoroughly dried, nettles make excellent hay with a protein content equivalent to lucerne/clover. Despite the stalky nature it is well digested by stock animals even pigs, fowl and rabbits. Common nettle has been used as a food plant when young and tender. The plant accumulates iron, calcium and magnesium and is considered to have medicinal value. Fibres from the stem were used to make linen and ropes.
Common nettle is an important alternative host of carrot fly and removal of nettles from hedgerows has been suggested as a means to suppress the pest. However, a range of aphid species that are fed on by beneficial predator insects also infests it. Common nettle is the main food plant for the caterpillars of several butterfly species.
Common nettle flowers from May to September. Flowering on individual plants is protracted and may last several months. Plants do not flower in their first year. Plants bear only male or female flowers that are usually wind pollinated. Flowering is inhibited by drought and shade. Common nettle also requires long days to stimulate flowering. Plants cut down in flower do not produce viable seed. Plants cut when the perianths are green but with the seeds at the milk stage, ripen seeds that germinate normally.
Seeds are able to germinate immediately on a bare soil in full sunlight but germination is delayed in closed vegetation. Seeds sown in field soil and cultivated periodically emerge sporadically through the year with a peak in April.
Seedlings appear from March onwards mostly from bare soil. The concentration of phosphate in the soil can influence seedling distribution. A low concentration can restrict early growth. Nettle seedlings grow rapidly in the first few weeks to stay above the developing vegetation.
Common nettle has tough yellow roots and creeping stems rooting at the nodes. The horizontal shoots develop a short distance below the soil surface. New rhizomes are formed in late summer or autumn from older rhizomes or from the stem bases of aerial shoots. They continue to grow until the death of the aerial shoots and they then turn upwards to form new shoots. The shoot tips may die back if frosted. Under prolonged drought conditions, vegetative growth is restricted. The plant overwinters as rhizomes with short green shoots.
Persistence and Spread
Abundant seed is produced, most is short lived but some viable seeds remained after 5 years even in cultivated soil. Seeds have been recorded in large numbers in the soil beneath pastures even when the plant was poorly represented in the vegetation. Seed viability was not affected by dry storage in the first 2 years.
The rootstock is tough, creeps extensively and enables the plant to spread rapidly. Rhizomes broken up by cultivation readily re-root. The seed enclosed in its perianth can catch on clothing and animal fur to aid dispersal. Common nettle seed has been found as a contaminant in samples of grass seed. Common nettle seeds are ingested by worms and excreted in wormcasts. Seeds are also dispersed in the droppings of cattle deer and magpies. The seeds can float in water for one week.
Control is by removing the rootstocks as thoroughly as possible when nettle patches are small. The collected material should be burnt. Repeated hoeing will exhaust the rootstocks eventually. Seedlings may be destroyed by frequent surface cultivations in spring and autumn. Common nettle cannot tolerate regular cultivations at rhizome depth. The shallow creeping rhizome does not regenerate well after repeated fragmentation. In grass, regular cutting beginning when shoots appear in spring and repeated each time shoots reach 6-12 inches should effectively destroy it.
In a clover/grass pasture, it was noted that common nettle was more likely to be associated with areas where clover was dominant than where grasses made up the majority of the vegetation cover. In unimproved pasture, common nettle increased under annual cutting for hay.
The regular trampling of cattle can wipe out common nettle. Salt licks around nettle clumps will attract stock to trample the weed. Overgrown areas of nettle are best cut in dry conditions to allow the surface roots to dry out in the sun and wind. On grazing land, stock will readily eat cut and wilted nettles but avoid the growing plant. Rabbits also avoid it.
Updated: October 2007