Annual nettle, burning nettle
Urtica urens L.
Annual Broad-leaved Weeds
Small nettle is a summer annual found on cultivated ground and waste places, particularly on light soils. It occurs up to 1,650 ft in Britain and is commoner in the east. It is favoured by soils with a high organic matter content. The presence of small nettle is considered to be an indication of the need for lime. Small nettle is intolerant of heavy shading.
It tends to be a weed of horticultural land and causes considerable trouble to growers of crops that are hand harvested. Small nettle is common in sugar beet crops in East Anglia and in the field margins.
Small nettle is important in the diet of many farmland birds. It has similar medicinal and therapeutic uses to the common nettle, U. dioica.
Small nettle flowers from June to November. The flowers are wind pollinated. Seed is set from June onwards but plants continue to grow and produce further flowers until killed by frost. The average seed number per plant is around 1,000 but a large plant can have up to 40,000 seeds. Small nettle can be found in fruit for 4 months of the year. The time from germination to fruiting is around 100 days.
Seedlings emerge from March to October with peaks in April and July. Seeds produced early in the year may germinate at once those shed later germinate the following year. Buried seeds require light for germination but just a 5 second flash is sufficient. Seeds germinate well in partial shade but bright light inhibits germination.
In sand and peat soils most seedlings emerged from the surface 30 mm with the odd seedling emerging from as far down as 60 mm. In a sandy loam soil all seedlings emerged from the top 45 mm of soil with the majority from the upper 20 mm.
Persistence and Spread
Small nettle seeds mixed with soil and left undisturbed declined by 61% after 6 years but in cultivated soil the loss was 96%. Seeds recovered from excavations and dated between 20 and 100 years old are reported to have germinated.
The seeds have a persistent perianth that may catch on clothing and fur to aid dispersal. Viable seeds have been found in cattle droppings. Small nettle seeds have been found as contaminants of vegetable seeds.
Regular and frequent hoeing is required to prevent small nettle seeding. It is absent from habitats that are mown or grazed. Weed numbers may increase following an application of manure.
Small nettle seedlings with 2-6 leaves are susceptible to flame weeding. Seedlings are also sensitive to UV radiation. The seeds are killed by soil solarization. Small nettle is not eaten by rabbits.
Updated November 2007.