Common knotgrass

Common Knotgrass

©Philip Precey

Common knotgrass

Scientific name: Polygonum aviculare
Despite its name, Common knotgrass is not a grass, but is actually related to the docks. It has wiry stems that grow along the ground, and is a weed of waste ground, gardens and arable fields.

Species information


Height: up to 60cm

Conservation status


When to see

May to October


Common knotgrass is found along the seashore, on waste ground, fields and roadside verges, and in gardens. This widespread plant has tiny, pale pink flowers that are very easy to miss as they appear so close to the stem; it blooms from May to October. Common knotgrass is also known as 'Iron-grass' because of its tough, wiry roots that make it especially hard to pull up from the ground.

How to identify

Common knotgrass has oval, leathery leaves of varying sizes, and tiny pink flowers that arise where the leaves join the wiry stems. It often grows horizontally along the ground.


Found throughout the UK, but less common in North East England and North East Scotland.

Did you know?

Common knotgrass can be used to make dyes of indigo, yellow and green.

How people can help

Although they might not look especially wildlife-friendly, our roadside verges, railway cuttings and waste grounds can provide valuable habitats for all kinds of plants and animals. The Wildlife Trusts are involved in many projects to make these places as beneficial for wildlife as possible. We have a vision of a Living Landscape: a network of habitats stretching across town and country that allow wildlife to move about freely and people to enjoy the benefits of nature. Support this greener vision for the future by joining your local Wildlife Trust.