Knotgrass
Broadleaf annual weed
Knotgrass is a tough, low annual weed that thrives where soil is compacted or regularly trodden. It spreads in wiry mats over paths, bare ground and thin lawns, remaining inconspicuous until established. Its resilience in hard ground and plentiful seed make regular early removal much more effective than waiting for a large patch.
How to identify it
Knotgrass has slender, tough, branching stems that usually lie along the ground and spread 10 to 60 cm. Small blue-green leaves are oval to narrow, alternate and attached at swollen stem joints, or knots. Tiny greenish-white to pinkish flowers sit in the leaf joints and are easily overlooked. Papery sheaths surround the joints. It forms a thin taproot with fibrous side roots, which can penetrate compacted soil. Mature plants make dense, wiry mats that resist casual pulling.
Where it grows
It is widespread in UK gardens on compacted paths, drive edges, paving cracks, thin lawns, hard-standing areas and dry vegetable plots. Seedlings emerge mainly from late spring through summer as the ground warms. It favours open, trodden soil where other plants struggle, particularly places repeatedly cleared, walked over or left bare.
Why it is a problem
Its close-growing stems occupy bare ground and compete with low crops and young plants. Knotgrass tolerates poor, compacted conditions, so it often persists where routine hoeing is difficult. Plants seed freely and the seed can remain in soil, creating repeat problems after paths are disturbed or vegetable beds are cultivated.
How to control it
Lift young plants by hand before seed forms, loosening compacted ground first so the taproot comes away. Hoe seedlings in dry weather where the surface is workable, then allow them to dry. Improve compacted bed soil with organic matter and avoid leaving cultivated ground bare. Mulch planted areas and use light-excluding covers on vacant plots. On paths and hard edges, remove small plants repeatedly before they root deeply and replenish the seed bank.
Commonly confused with
Knotgrass may be confused with prostrate knotweed or other small Polygonum relatives. The wiry prostrate habit, alternate leaves and papery sheaths at each swollen joint are useful features. It can also resemble young bindweed, but bindweed develops arrow-shaped leaves and later twining stems.
Knotgrass: frequently asked questions
How do I identify knotgrass?
Knotgrass has slender, tough, branching stems that usually lie along the ground and spread 10 to 60 cm.
How do I get rid of knotgrass?
Lift young plants by hand before seed forms, loosening compacted ground first so the taproot comes away.
Where does knotgrass grow?
It is widespread in UK gardens on compacted paths, drive edges, paving cracks, thin lawns, hard-standing areas and dry vegetable plots.
General guidance for UK gardens and allotments, focused on prevention and non-chemical control. For a confirmed identification, the RHS or a local garden centre can help. Page updated 19 Sep 2026.