What is Himalayan balsam?

Himalayan balsam is an invasive non-native plant that originates from the west and central Himalayas which was introduced in the UK as a garden plant in the early 19th century. The plant was first recorded in the wild in 1855 and is now a naturalised plant that is widespread across the UK.

How do you identify Himalayan balsam?

Growing in moist and semi-shaded damp places, Himalayan balsam commonly exploits linear corridors such as rivers or disused railway lines, as well as thin and wet woodlands. 

When in flower, Himalayan balsam is easy to identify. You will have most likely seen huge pink swathes along the banks of rivers and ditches – trumpet shaped, sweetly scented pink flowers with spots and markings inside. Himalayan balsam can grow up to 2-3 metres in height. Very young plants have a light green, almost translucent stem, and as the plant grows the stem turns red. The stem is hollow and brittle, with the larger stems making a popping sound when snapped.

What’s the issue with Himalayan balsam?

Whilst it may be aesthetically pleasing, Himalayan balsam has a massive detrimental impact ecologically.

Because it tolerates low light levels and shades out other vegetation, it can gradually impoverish habitats by killing off other plants. It also swiftly out-competes our native plants due to its ability to rapidly reproduce and grow in dense stands, completely taking over banks along waterbodies. Each plant can produce a minimum of 500 seeds that can remain viable for up to two years – these are dispersed widely, as the ripe seedpods can shoot their seeds up to 7m (22ft) away. These seeds cover surrounding banks and can even travel in water to seed further downstream. Seeds may also be transported unintentionally by wildlife, machinery, grazing livestock and people using sites for recreation.

Although the plant is known for attracting pollinators, it has little to no ecological value for most of our insect species. Himalayan balsam produces a large amount of nectar and pollen, which may attract insects away from our native plants, which could result in less pollination of native plants. This then has the further impact higher up in the food chain of insectivores having less to eat – the loss of our native plants where Himalayan balsam has taken over means that there are less plants for insects to feed on and to use for their lifecycles.

Below are three photographs of the same bank that shows the bank blanketed in balsam, the bare bank after pulling it up and then the bank having regenerated with native species a month later. This shows how Himalayan balsam easily takes over and pushes out native species.

Ditch/riverbank riparian zones (wetlands adjacent to rivers and streams) are an important ecological habitat, as they are the interface between terrestrial and aquatic environments. They provide an ecological service of promoting and maintaining the of geomorphic stability of banks and filtering any pollutants entering the water. When Himalayan balsam takes over, the bank becomes unstable as the plant is shallow rooted and cannot hold the soil together. Himalayan balsam is an annual plant and over the winter the plants die back. This leaves banks bare, causing an increase in sediment erosion and an influx of nutrients and organic matter into the water. This reduces the quality of the water and affects aquatic flora and fauna.

How do we manage Himalayan balsam on our reserves?

We try to manage the spread of Himalayan balsam on our sites through non-chemical control – pulling up the plants from their roots and then composting them down, which is more effective to pull up the whole plant. Cutting the plant down doesn’t always work, as it needs to be cut below the first node to stop it regrowing. Often the stem of the plant can grow sideways along the ground before shooting upwards, and cutting by hand or machine will often miss the lower stem. Managing this spread is a never-ending battle, as the plant can easily spread from neighbouring land if it is not being managed or controlled.