Volunteer & Log Sightings Of Invasive Species

Himalayan balsam has become a persistent problem in North Wales for decades, particularly along rivers, because it thrives in damp soils and spreads quickly through watercourses. Each plant can produce between 500 and 700 seeds, which are explosively released and can be carried downstream, helping the species colonise new areas with ease.

Its tall, dense stands outcompete native plants, reducing biodiversity and leaving riverbanks dominated by a single species. When the plants die back in winter, the bare soil left behind is more vulnerable to erosion and sediment run-off, which harms water quality and aquatic habitats. This cycle has made Himalayan balsam one of the most widespread invasive species impacting rivers in the region.

Volunteer call out : log sightings

To help organisations like ours and community action groups you can log sightings on INNS MAPPER which allows us to strategically target the worst areas. Logging sightings through the INNS Mapper app and now is a great time to log as the plant is flowering making it easy to identify.

Himalayan Balsam Control: Volunteer Guidelines

Species information

• Himalayan balsam (Impatiens glandulifera) is a non-native invasive species introduced to the UK in the 19th century; It is now widespread along rivers, in wetlands, and on disturbed ground.

• Each plant typically produces between 500 and 800 seeds, although under optimal conditions, an individual plant can produce up to 2500 seeds. The seeds are explosively released and land within about 7 metres of the plant.

• When seeds fall into a watercourse or the watercourse erodes soil that contains seeds, the infestation is spread downstream.

• Himalayan balsam outcompetes native vegetation, forming single-species clusters that die back in winter leaving exposed soil. It thereby contributes to riverbank erosion and the loss of native species.

• Plants are very easily pulled by hand due to their shallow roots. Large areas can be controlled by cutting / mowing below the first node along the stems.

• Seeds remain viable in the soil for up to 2–3 years, forming a persistent seed bank. Therefore, to effectively eradicate an infestation, thorough control for several consecutive years is required. Nevertheless, every plant that is pulled helps to control the spread.

Before You Start

• Identify problem areas. Remember that the seeds spread along watercourses and therefore always try to find the most upstream occurrences in a catchment and work from there downstream.

• Get Landowner Permission: Always secure permission from the landowner or land manager before starting work. 

• Safety Briefing: Volunteers should wear gloves, long sleeves, and sturdy footwear. Be mindful of uneven ground, hazards of working near water, and plants such as nettles or brambles – long trousers are recommended.

Best Time to Pull

• Main sweep: Late May to early July
  Plants are tall enough to identify but haven’t yet seeded. Pulling at this stage prevents seed spread and gives native plants a chance to recover.

• Second sweep: Late July to early August
  A follow-up is crucial to catch late germinators or missed plants. Removing these prevents them from restocking the seed bank in the soil. 

• Pulling should stop once plants have started to seed, usually from mid-August onwards and likely earlier if there was no pulling in early summer, as the activity can spread seeds further. Instead, carefully cut or crush seed heads and dispose of plants without shaking them.

What to Do with Pulled Plants

• Leave in piles at the site but away from water: 

• Stack pulled plants in heaps where they will rot down quickly. To reduce the risk of some pulled plants re-rooting, try to place them upside down with the roots facing up. You can completely avoid re-rooting by placing piles on a tarp. However, the tarp will need to be collected after a few weeks to avoid plastic littering, so this is mainly suitable for small operations close to home. Avoid placing piles on top of rare native plants.

• Keep piles well away from watercourses and tracks or footpaths to prevent accidental spread 

• Don’t take the plants elsewhere, don’t compost them at home or dispose of  any invasive non-native plant in your brown bin or at a local recycling centre as seeds may survive and spread. 

Organizing Volunteers

• Briefing: Explain plant ID, pulling technique (firm but gentle to remove the whole plant including the shallow root), and disposal method.

• Supervision: Have team leads to guide and check for missed areas.

• Record keeping: Note dates, locations, and volume of plants removed (or take photos) to track progress and help plan future sweeps. A handy tool for recording both sightings of invasive non-native species and management operations is the app INNS Mapper. You can also use the map on the app or website to see other people’s records, for example to help identify problem areas.