Himalayan Balsam - the scourge of our rivers!

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Himalayan Balsam – the scourge of our rivers!

Balsam plants can reach 3 metres in height

Every year in May we get a little obsessive about Himalayan balsam. For those who don’t know it, this is a highly invasive plant which has taken over river banks, becks and ditches across the country. Whether it’s the Ouse, the Foss or local becks like Tang Hall and Osbaldwick, you don’t have to go far without seeing its striking, tall pink flowers during summer months.

You may see the flowers full of bumblebees and rightly wonder how it can be anything but good. One of the main things that sets it apart from many of our native river sides flowering plants is that is it an annual, meaning it only lives for one season before dying completely, rather that perennials which ‘die back’ every year but grow again from the same root system each year. For an annual like balsam it can only survive through its offspring, by producing seeds which lie dormant during our cold winters only to come to life and germinate into new plants when the temperatures rise in the spring.

Each seed pod holds 4-16 seeds meaning one plant could produce 100s of seeds if not managed

In theory, this could mean that if you managed to clear every growing balsam plant in one year before it sets seed, you would completely eradicate it from your site. Unfortunately, in practice this is much harder than it may sound, especially on sites where it has been not previously been managed. Balsam can easily take over an area, out-competing other native plants year after year until they die off, creating what is known as a monoculture. When the balsam dies off after seeding, and nothing else has been able to grow, it leaves large areas of exposed soil along waterways – just in time for winter floods.


It really does get everywhere and tolerates shade so the most time consuming job is often having to scramble under rose bushes and brambles to get them. As well as growing through bramble patches and in rotting tree bark, we also find it growing through items of buried waste like this metal wire!

I have been at St Nicks nearly 11 years and Himalayan balsam was thriving on the becks and other habitats at St Nicks way back then. After a number of years of sporadic management, it has only really been in the last 5 or 6 years that we have implemented a more rigorous and systematic management plan. This plan includes working upstream to down (such an obvious thing to be doing to manage a riverside growing annual but hey, we got there in the end!), clearing from other sites upstream, and most vitally, trying to return to each balsam area after clearance to continue to remove any that were missed or regrowing.

As soon as seed pods starts popping we stop clearing new areas (as we’d end up doing more harm than good by spreading the seeds ourselves) and concentrate on repeat visits to where we have already worked. And while all this requires a huge amount of time and resource to implement, the good news is that this plan is noticeably working! As hoped, we are seeing fewer and fewer plants growing the following year in areas we had successfully cleared, but all it takes is one missed plant which gets chance to seed to ensure there are more plants again next year.

And considering the way balsam grows, plus the fact it can still be found flowering and seeding in early autumn, 1 or 2 plants are always likely to slip through the net. Clearing an area so only a handful of plants are left each year is real progress though, especially areas that in previous years had hundreds.

We collect balsam into builders bags and remove from the bank sides so plants can’t re-root or get washed down stream.

We have a number of balsam ‘pits’ around the nature reserve so we can safely dispose of the plants without having to drag them too far.

As hopefully you can tell, eradicating Himalayan balsam from a site once it has taken over is not easy. So imagine a year without much or any management and the devastating effect that could have – it could basically set us back years and make previous years’ efforts a waste. And that was the potential prospect we faced this year due to Covid-19.

There are still areas downstream which we haven’t got to managing yet. Here you find ‘forests’ of balsam which prevent other plants from growing

All of a sudden we had no volunteers (understandably due to safety concerns) and a partially furloughed member of our Natural Habitats Team (there are just two of us!).

Thanks to emergency funding from National Lottery Heritage Fund our Volunteer Coordinator Maria has been able to focus her time on combating balsam.

And as well as balsam, we had all the other regular management tasks to keep the nature reserve safe and open. Thankfully, emergency funding for our sector arrived from the National Lottery Heritage Fund and provided the financial security to be able to focus our efforts where most needed, as well as trialing new ways to have volunteers on site which provided vital assistance when we most needed it. Fast forward a few months and we are coming to the end of our most successful balsam season yet.

As well as getting further downstream at St Nicks than we ever have managed, we have cleared all upstream areas of both Tang Hall and Osbaldwick Beck that we can access. Hopefully this means in future years we’ll have lots more wildflowers growing along the banks of our becks for wildlife to enjoy.

Post written by Natural Habitats Manager, Jonathan Dent. If you’d like to support St Nicks conservation efforts, please consider making a donation. Thank you.


20 August 2020 | Categories: Spotlight on... | Tags: Himalayan balsam, wildlife, york becks