As the seasons change, the vibrant colours of summer give way to the rich russet hues of autumn. Along the edges of our chalk streams, water mint plants are displaying their last splashes of pinkish purple. From July to October, this native plant brightens up riverbanks with its dense clusters of tiny flowers. Even in the colder months, you can still spot its square stems and hairy, jagged-edged leaves.

Water mint is one of about 15 mint species that grow in the UK, although many of these are hybrids. Did you know, for example, that peppermint is a cross between water mint and spearmint – another of our native mint species? In fact, peppermint plants can sometimes be found growing in the wild near their parents.

As its name suggests, water mint loves to grow in damp places. It favours ponds, bog gardens, marshes, floodplain meadows, wet woodlands, and the margins of rivers. In an ideal habitat, it can grow to over 50cm tall and spread sideways through rhizomes (thick stems that grow underground) and runners (thin stems that grow on or close to the ground).

Like other plants that grow in and around our chalk streams, water mint plays a key role in protecting the habitat. It offers shelter to animals that frequent the margins, like juvenile fish, small mammals, and emerging riverflies. Its root system helps to stabilise the bank and shield it from erosion, which saves fish eggs from being smothered by sediment. Its flowers provide nectar to peacock, comma, and small tortoiseshell butterflies, while its leaves are a favourite food of mint leaf and green tortoise beetles.

As with the kind you can buy from the supermarket (which is usually spearmint or peppermint), water mint has aromatic leaves that can be used to make flavourful drinks and meals. But it’s best not to use wild water mint for this purpose, because there may be pesticides, herbicides, or pollution in the area. Instead, see if you can safely get close enough to detect its bright and refreshing scent – a real treat on an autumn walk!

If you’d like to learn more about chalk stream flora and fauna, why not check out the Watercress and Winterbournes scheme? We're enhancing chalk stream habitats on the uppermost tributaries of the Rivers Test and Itchen, which includes helping plants like water mint to thrive.

Explore Watercress and Winterbournes