Kingston University Biodiversity Action Group

Balsam Basing on World Environment Day

On the lead up to World Environment Day, Dedicated students fromKingston University joined up to help clear Himalayan balsam Impatiens glandulifera – conducting a balsam bash on the banks of the Hogsmill River. 

The history of balsam

Himalayan balsam was a garden plant in the 1830’s which soon escaped into the wild due to its explosive reproductive technique – its seed pods are designed to explode when touched and in hot weather – sending around 2500 seeds per plant into the surrounding areas.

It was also spread deliberately by people, as such it became rapidly naturalised around watercourses in and near towns and cities, with watercourses helping to spread the seeds far downstream of the plant.

It is classed as a significant invasive plant in at least 15 European countries including the UK.
ARKive image - Himalayan balsam flowers
See more photos of balsam by visiting ARKive

The main issues:

Shading out native plants - This tall plant can easily shade out native plants in the surrounding area.
Reducing pollination in native plants - Balsam produces more nectar then native European species, as such it attracts pollinating insects away from native plants. In areas where there are large stands, research has shown that this competition has resulted in reduced seed production in native plants.
Riverbank erosion - When the large stands of shallow rooted balsam die back in winter, the resulting bare ground is much more vulnerable to erosion flows.

Shallow roots of balsam - breaks easily allowing plants to regrow from cleared areas

Balsam bashes need to occur before the plants produce seed ponds, and ideally before they flower, this is why May and June are the balsam bash months.

KU's Balsam bash of the year started on the 4th of June and ended on the 5th of June on World Environment Day (WED) where we posted a quick mash up of the all of our work. 

Volunteers got stuck in clearing the balsam from the banks. Firstly we removed all of the balsam in the newly planted re-naturalised bank by Knights Park in the rain. We then worked  on the south bank at Middle Mill. Concentrating on the large plants which were close to flowering as well as trying to remove as much of the root mater and small plantlets as possible. 

Philip getting ready to do some serious balsam clearance

Amy hidden in a field of balsam

Amy and Rahma making great strides on getting the balsam roots out

Harriet clearing plants onto the path ready for bagging
Bagged plants waiting to be joined by more balsam before being collected
 The end of the first afternoon  - Go team balsam!!
By the end of the first afternoon, dedicated volunteers had worked through short showers to clear large areas of balsam... 

Areas where large stands of balsam were cleared (green boxes),
 with the targets for the second afternoon identified (red circles) 
...and the refreshments at the end, along with the sunshine were very welcome.

George the Middle Mill Cat, congratulates the volunteers by getting petted!

On the second afternoon, team two cleared through their targeted areas on the south bank of the Hogsmill;  as well as locating as many of the small plant-lets hidden amongst the downed nettle and working around the Japanese knotweed Fallopia japonica - which have to be dealt with by specialists. 

Garima avoiding most of the nettles while clearing the small balsam plants

David bags up the pulled plants and roots at the water side
Garima moving the packed bags to the stock pile
we managed to double the amount of cleared balsam, aided by the lovely sunshine 
By the end of the afternoon on WED we had cleared the targeted areas...

...and have a nice certificate to show for our efforts
But there is plenty more to do, at both Middle Mill and Knights Park around the older banks where the plant has established. 

David looking out at the opposite bank with its balsam 

We need volunteers to work from the bank and the river to try to reach the plants which are growing at the water’s edge and up the bank to help reduce the balsam seed bank on our sites and help stop its continued spread downstream.

Sign up for our next Balsam Bash on the 18th of June and enjoy a picnic at the end of the bash.

Staff and students – sign up via the KUSUvolunteering portal to allow the University to keep track of your volunteering hours for student and staff awards. 

Local community and alumni – please register for the event by emailing

If you are not free on the 18th, there are balsam bashes happening all over London at the moment. Some of the ones carried out by other organisations in Surrey listed can be found here.

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