Herb bennet (Geum urbanum) or wood avens has yellow, strawberry-like flowers followed by distinctive fruits with burrs. The flowers are attractive to insects and the roots and leaves are used by herbalists but it can be a common weed of shady borders.
Botanical name Geum urbanum
Area affected Shady, moist borders and grassland
Caused by Regenerates from root fragments and seeds
Timing Rosette of leaves in winter, flowers from May- Aug; treat spring to autumn
What is herb bennet?
Herb bennet is a native perennial that favours moist soils in woodlands, hedges and shady places and especially in calcareous soils. The bright yellow flowers with five petals are carried on nodding stems above the foliage and although self-pollinated are attractive to small beetles. Herbalists use the roots and leaves and the roots were used to flavour ale, while the Romans used it as a substitute for quinine. Herb bennet can be allowed to grow in wilder areas of the garden. Learn more about making the most of lawns as a wildlife habitat and ways to help our bees;
Herb bennet is generally distributed throughout the British Isles except parts of central and northern Scotland. It can regrow from root fragments and self-seeds, making this a common weed. This page looks at options for the gardener when herb bennet is becoming a problem.
Over winter herb bennet forms rosettes of leaves with five to three rounded lobes; the largest lobe at the tip. Leaves pinnate with rounded leaflets are hairy. Height to 60cm (2ft). Produces yellow flowers from May-Aug, 5-20mm (¼-¾in) across, resembling buttercups but, being in the rose family, it is not related.
The flowers are followed by fruits held in spherical clusters and are burred with red hooks.
First, consider whether this can be done using non-chemical means such as digging out. Where this method is not feasible, chemical controls may need to be used.
The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
As this is a perennial plant complete removal of the weed by hand is the best cultural control. If possible do this before it sets seed.
There are no specific recommendations for the control of herb bennet, although we assume that it is fairly resistant to most of the lawn herbicides available as this is the case for the closely related genus Potentilla.
Use a glyphosate-based weedkiller such as Round-up Fast Action. Glyphosate is a non-selective, systemic weedkiller applied to the foliage. It is inactivated on contact with the soil, so there is no risk of damage to the roots of nearby ornamentals.
As glyphosate is not selective in its action, it is essential to avoid spray or spray drift coming into contact with garden plants. If treating weeds in the immediate vicinity of garden plants, apply carefully using a ready-to-use spray formulation in cool, calm weather. Branches or shoots can be held back, using canes, or by covering or screening while spraying, but make sure that the weed foliage has dried before releasing branches or removing the covering.
Glyphosate is most effective when weed growth is vigorous. This usually occurs at flowering stage, but before die-back begins.
In rough grassland
If the weed is growing in grassy areas, then the herbicide SBK Brushwood Killer can be used, as this would leave the grass unharmed. The susceptibility of Geum urbanum to SBK is not known, but as the weedkiller gives good control of the closely related silverweed (Potentilla anserina) it is likely that Geum will also be knocked back. This herbicide is systemic, travelling from the weed foliage down into the root system. SBK will damage any broad-leaved plants however (e.g. wildflowers) and so should only be used in grass where such action is acceptable.
Spring or summer are usually the best seasons to obtain good control of perennial weeds. More than one application may be necessary to gain control. Seedlings will not be prevented from germinating so be sure to catch these either by hand weeding or with a herbicide when they appear. Always follow the manufacturer’s instructions when using weedkillers.
Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.
Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 1a and 4)
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