A Spotlight on Himalayan Balsam

Of all the wildflowers I enjoyed as a child, Himalayan Balsam is one of the most memorable. Mainly because, in my youth, popping the little green grenades produced by the plant when it goes to seed, was once the most exciting feature of my woodland walks in late summer, when the pods come to fruition. Popping the pods and watching the small, brown seeds rain like confetti, ever entertaining. Even now, knowing fine well the havoc brought about by the species, balsam has a certain appeal. It’s subtle, orchid pink flowers equally as beautiful as any of our native blooms and the sickly sweet smell emitted by the plant, particularly on rainy days, always welcome. As is the sight of bumblebees and wasps, stained white by the plants pollen, frantically buzzing between the ample blooms in the summertime..

This said, while I do somewhat admire Balsam, both for its beautiful and its sheer tenacity, it has quickly become one of our most maligned invasive species. Holding an undisputed place in the inglorious triumvirate of our most problematic plants – the other two places going to Japanese Knotweed and the monstrous Giant Hogweed. The sight of Balsam, along our waterways and in our woods, is not unusual.  Indeed, my local woodland is positively bursting with it. Something which, recently, caused me to look a little further into the plants history and the problems caused by it in the British ecosystem. The results of which can be found below.

Origins

Himalayan Balsam, or Impatiens glandulifera, to use its scientific name is a large, annual plant species native to, as its name suggests, the Himalayan mountains of East Asia. Growing alongside the colossal peaks and quaint streams of Nepal, Myanmar and other nearby nations.

The story of balsam in the UK is an all too familiar tale, brought to our shores in 1839 to adorn the gardens of the aristocracy. Many of whom, during the Victorian era were in the midst of a “wild gardening” phase. Something which lead the green-fingered elite to embellish woodlands with exotic blooms capable of not just withstanding the British climate, but spreading to form large, ornamental stands. A process which lead to the widespread planting of many species that we view as detrimental today and perhaps best described by William Robinson, author of ‘The Wild Garden‘ who writes:  “the principle of wild gardening was naturalizing or making wild innumerable beautiful natives of many regions of the earth in our woods, wild and semi-wild places, rougher parts of pleasure grounds, etc“

These initial introductions were undoubtedly responsibly for the spread of balsam into the British ecosystem, something which had already taken place by 1855. A mere fifteen years after its initial introduction. This widespread, ornamental, planting of balsam continued well into the 1900’s though as the decades advanced, I.glandulifera began to appeal to more than just those possessing grandiose gardens. Due to the speed at which it grows, and its tendency to exist in large thickets, balsam soon became a favourite of everyday gardeners also. Mainly used to cover large areas of exposed ground – the plant itself undeterred by poor soil, rubble or pollution – and, according to some sources, also as a means of replicating the vibrant gardens of the elite. With a single balsam seed enough to produce some 1000 plants in a mere five years. Indeed, by 1909 the species was a firm favourite in country gardens. A trend which continued up to the modern day with balsam still being purposefully distributed until the late 1990’s (and probably later). The accounts below, taken from the paper shown at the end of this article, standing testament to this:

• In the early 1990s, Mrs Gubbin of Reading collected seed from a friend’s garden, introduced it to her own garden, and from there spread it to other gardens and to local hedgerows. She considers it very useful for filling in empty spaces and providing background for planting.
• Mrs Holms of Newcastle-upon-Tyne, in the 1990s collected seeds from her son’s garden in Snettisham in Norfolk, for her cottage garden at Belsay in Newcastle. ‘Now I am gradually furnishing all the gardens in the village with these plants for the seed fly everywhere.’
• Mrs Guych of Birmingham recalls balsam in their garden c. 2 miles from the centre of Birmingham in 1917. In the late 1950s she took it to a garden in Ledbury (Herefordshire). She also transferred it in the 1990s, from the River Trothy in Monmouthshire, to a garden in Solihull.
• In the 1990s Mrs Edwards of St. Albans received one plant for her garden from a neighbour, apparently from seed from St Lucia, and has since sent it to Redbourn, to Essex, and to Luton.

The Problem

The posed  by balsam in the UK centers on how quick the species spreads, the very reason it became popular with Victorian gardeners in the first place. As I have said, balsam seeds spread when the pods in which they are held explode, a process known by some as “ballistic dispersal“. This allows the seeds of the plant to spread up to four meters from their original location and can quickly lead to stands of balsam engulfing whole areas of the landscape. Also, due to the tendency of balsam to grow near water, the seeds often find themselves carried many miles downstream of their original location. The seeds themselves remaining viable for up to two years, meaning they can travel great distances before making landfall and growing anew.

The explosive nature of balsam is however, only half of the story. Where the species takes root it can have serious implications for the ecology of that area – mainly through direct competition with native ground flora. Competition which balsam, due to the speed at which it grows, often wins. Quickly forming a dense canopy which shades out and smothers other plant species. On top of this, it would appear that many native pollinators actively favour balsam over native species, further reducing the ability of other plants to seed and therefore, spread. Finally, as an annual, balsam is subject to die backs in winter and where it the only species in residence – as is often the case due to matters mentioned previously – can leave river banks bare during this period. Thus making them liable to erosion, particularly during floods.

Can balsam be controlled? Well, yes, though the methods currently being deployed against the species appear inadequate at best. An assumption based on the continued spread of the species across Britain. Among these methods, pulling is often preferred. A process which involves pulling out the plants – which are shallow-rooted and thus easily removed – early in the year, before they have the chance to flower. Something which has been shown to destroy stands of balsam within 2-3 years. Elsewhere, strimming is also an option, though it must be undertaken regularly, before the plant has flowered. By far the most effective means of controlling balsam however appears to be chemical control, with both spraying and injection often used. Though the latter is both costly and time consuming and the former, coupled with the close vicinity of water bodies, often comes with pollution risks.

Source Material and Further Reading: Himalayan balsam – the human touch. Ian D. Rotherham (2000)