Darren Greatbatch, Specialist Advisory Manager, Amenity & Invasive Weeds, at Environment Controls.
Last reviewed on .
Invasive and hard to control
Shallon (Gaultheria shallon), also known as salal is a dense, evergreen shrub non-native to the UK, originating from North America. It has become highly invasive in parts of the UK, where it poses significant ecological challenges – specifically to our native woodlands. Once established it is extremely difficult to control, and if left unchecked it makes tree regeneration impossible.
With forest fires becoming more of threat due to climate change – Shallon will be one of the surviving species. Whilst the above ground vegetation will die off if burnt, the underground rhizome can survive and will regenerate new plants. The biggest threat is to landowners and forestry commissions, where this plant can cause significant environmental harm.
Shallon can grow up to 10 feet tall, its glossy evergreen leaves and pretty white or pink flowers can be appealing to gardeners – but beware it needs to be kept under tight control as it spreads vigorously by underground rhizomes, forming dense, almost impenetrable thickets.
In spring to midsummer, it produces small, urn-shaped white or pink flowers, followed by edible dark-blue berries in late summer that can be eaten fresh, cooked or dried.
Invasiveness and impact
- In its native range, Shallon is a moderate competitor, but outside its native range, especially in the UK, it is highly invasive – and a real threat to UK forestations.
- It quickly forms dense thickets that outcompete native plants, reduces biodiversity, and inhibit forest regeneration by physically blocking seeds from reaching the soil and monopolising nutrients and light.
- Can alter nutrient cycling by releasing tannins, further impacting native plant communities.
- Its spread threatens key woodland species and ecosystems, as seen in the UK where it endangers native ants that contribute to carbon capture.
Can it be controlled?
Shallon is a problematic invasive species in the UK, forming dense thickets that suppress native vegetation and disrupt woodland ecosystems. Once established, Shallon is very difficult to control but effective management with targeted herbicide application at the right time of year is successful. Mechanical removal (by excavation) is challenging due to its extensive rhizome network, and often location (if located in dense forestry areas) but can be done by a specialised contractor.
If you manage woodland or forestry land you may have this invasive plant. Ask us for a quote to have it treated or removed.