Monday, 12 December 2016

How to control Himalayan Balsam, Impatiens glandulifera


My alternative working title might have been along the lines of how to grow this beautiful plant much loved by bees.
Perhaps the two common names ‘Policeman’s Helmet’ and ‘Bee Bum Plant’ say it all. Undoubtably in places this plant is a nuisance and a real menace. The bobby encapsulates the stupidity of legislation against it. The bum bit being the beauty of bumble bees bumbling at the base of balsam flowers gathering nectar.

How on earth did such a beautiful plant get such a bad name?
It is a weed of disturbed land. Not cultivated farm fields. Farm field receive too much attention.Not established meadow land. The grass is too well established and is usually regularly grazed. Not established dry forest the canopy is too strong. Not neglected sites themselves overgrown with brambles and ground elder - they grow too well.

It is true that it is so strong growing that in certain circumstances weeds such as nettles are outgrown - not a bad thing? It is also true that where balsam is eliminated in wild situations coarser weeds tend to replace them.

Balsam and coarse vegetation are in competition 
Its natural habitat is described as ‘riparian’ and is the moist land alongside rivers and streams and near boggy places. Balsam is not aquatic and does not grow in the water.

Balsam is a weed of neglect. It is weed of stretched budgets where semi-amenity areas, country walks, and set-a-side sites receive inadequate and unskilled maintenance. It grows where stewards of the landscape have long been paid off by years of cost cutting. In particular it is a weed of disturbed loose soil. This annual plant must have late Winter vacant ground to newly germinate and start afresh each year. It is NOT a perennial like most noxious weeds.
It does not even germinate all the year round like many other weeds; only late Winter and Spring.

First frost and it is completely killed
Next Spring you have a clean start to get rid. This is the time to take charge 
Where balsam is a real problem

It likes plenty of moisture
It is usually a problem on wet sites. It is frequently found alongside rivers and streams. The main reason for this is that river embankments are frequently eroded and open soil is vacant for balsam seed to establish. It is to a degree a vicious circle when strong growing impatiens suppresses weaker growing plants and is alleged to outgrow desirable’ wild flowers. Each Spring strong growing impatiens seedlings have a field day! There is vacant soil and little competition. Impatiens’ secret weapon is copious  quantities of strong seedlings germinating all at the same time.
Is it fair to blame impatiens for river embankment erosion? It dies down in Autumn to leave erodible patches. It’s quite a chicken and egg situation. What comes first, the erosion or the weed?

It’s spread is not as efficient as suggested

It produces copious seed which when ripe is thrown all around
Impatiens throws out its seed in late Summer and Autumn by mechanical dispersal. Not very far! Perhaps five foot or so. Occasionally much more if a gale happens to be blowing. Its normal success is due to the density of self sowing. The odd distant solitary seedling will have a very difficult time and will usually fail to gain a foothold.

Note the grass suppresses the balsam seedlings. If mown, strimmed or grazed the balsam will die. If nothing is done over a season or two the balsam will take over
Nevertheless compared with the slow advance of most noxious perennial weeds, because it is a seed borne plant balsam’s spread is comparatively rapid. At individual plant level, the spread is perhaps two metres a year. On a regional level there are much greater advances.
You will read that balsam seed is dispersed by floating down the river. My friend Peter Williams did a test with his students and found that if you put the seeds in a bucket of water they sink like a stone! 
This does not mean that any plant seed might not be carried by water. Raging rivers will carry almost anything! Impatiens does spread alongside river banks but not as quickly as claimed - but  even so, with several years of no action look what you get!

In summary Himalayan balsam spreads if nothing is done and when landowners and managers just ring their hands and do nothing it will spread all the way down the river.
The spread is only remorseful if no preventative action is taken.

Himalayan balsam is very easy to control in the garden
No competent gardener should have this weed - if he does not want it.
It is a weed of large public areas where its control is restricted by rules, regulations, ignorance and bureaucracy. It is easy to control and has many vulnerabilities. Almost any common method of garden weed control works! The plant’s main weakness is its annual nature and with the very first frost it dies. 
Its seed germinates in Spring almost all at the same time. The seed  germination is prolific but only in this very first season. Little seed survives to the following year and I have read no reliable reports of seed surviving longer.
The key is to prevent this weed ever seeding! From germination you have three months to get rid of it before it starts to prolifically seed. You need to be vigilant, one large missed weed can next year produce 800 strong vigorous seedlings. If you have even one such large plant you are not really trying or you are a good gardener who actually wants to grow a small clump and is confident you can constrain it.

Here is a list of suitable ways to eliminate Himalayan balsam. None  of them work if you practice them on a single occasion - you are bound to miss some. You need to be alert to their appearance throughout the first (and second) year.

  • Hand pulling. This is very effective but inefficient on large areas. It’s easy to pull out but you will soon tire. In very wet weather if left on the ground the roots will re-establish. It is suitable on public areas for large teams of unskilled ‘volunteers’. If it is wet weather you need to remove and compost the weed. Whatever your overall weed control strategy be prepared to pull out the odd overlooked balsam or any growing through delicate plant treasures.
  • Hoeing. This is ideal if it is dry weather and balsam is not long germinated. Let the hoed seedlings desiccate and die. Go over again a few days later to find any you have missed. A few weeks later hoe any late germinators. Hoeing larger balsams is fine but starts to become hard work. Don’t hoe too deeply, instead sever them at ground level. There is no need to remove them.
  • Sickle them down. OK you don’t own a sickle but it is one of the very best methods. Bend your back and slice the weed very close to the ground. If you cut near enough  the weed won’t regrow and it won’t re-root either. It is extremely satisfying and speedy. If you do not cut close enough to the ground or the plants are nearing maturity there is a small chance of some regeneration.
  • Strim them! Adverse as I am to machinery it works extremely well on open spaces or amongst woody plants.
  • Mow them. Where there is easy access, impatiens does not stand a chance. On a large scale farmer’s mowers cover very large areas in no time at all.
  • Spraying. Coming from me you might expect me to claim it is the very best method. Not always so. Undoubtedly glyphosate kills them but it is very easy to miss seedlings and when bigger it is difficult to safely reach them amongst delicate plants. Don’t let anyone tell you that this weed needs to grow large to take up an effective dose! Seedlings are just as susceptible as larger plants. Like many other weeds if they are flowering when sprayed they will still have time to produce viable seed.
It’s good for the bees
Beekeepers are good citizens and are made to feel guilty by impatiens propaganda. Say it for the bees! Bees love impatiens! It makes excellent honey from copious nectar,  A single balsam flower produces more nectar than any other wild-flower flower. Honey bees and bumblebees distribute masses of pollen. September and October balsam flowers provide nectar at a very difficult time. With this late generous food source hives remain strong
It is levelled against impatiens that it diverts the bees attention from more desirable wild flowers. This is strongly disputed and is not very fair. When did you last see complaints about heather, clover and apples? Surely the fact that bee colonies remain strong is in the round far better for nature. It is a gross slander on bees that they pollinate and therefore help spread impatiens and neglect the wild flowers.
A  bee keeper, tongue in cheek, observed that government legislation that prohibits aiding and abetting the spread  of this weed makes him a criminal when his bees carry out pollination! 
This legislation is ill advised, ineffective, badly framed and fortunately toothless. Penalising gardeners (or bee keepers) makes no sense at all.

Why I disagree with legislating against this weed

  • It is a sledgehammer to crack a nut
  • It would be better to spend resources controlling  the weed rather than lining lawyers’ pockets
  • It does not work. 
  • Most likely culprits don’t even recognise the weed nor know how to contain it
  • It is difficult to define what constitutes a criminal offence and very few - or any - prosecutions will ever be made
  • The horse has bolted. Almost all gardens harbouring this plant received it by natural dispersal and did not plant it. It has been out there since the Victorians introduced it nearly 200 years ago.
  • Why pick out this weed for such measures when very much worse weeds such as nettles and brambles are accepted - even encouraged!
  • It creates a cash cow for cowboys
Far better to provide educational information and encourage gardeners to be responsible.

Five case studies
Case study 1 - Bolton Percy cemetery
There will be more room for sitting
The ditch alongside the graveyard rarely runs, dries out in Summer and does not go very far. As long as I can remember it has hosted a few balsams. For years they had not encroached into the cemetery as my routine weed control is glyphosate spraying. In recent years I have ‘allowed’ a few plants to grow as I rather like them. Only in rough areas such as ivy covered spaces. Three years ago I was complacent and allowed too many to seed. The following year the lower part of the cemetery was over-run by impatiens seedlings. 
I knew I could handle them and took along my sickle. In an hour I eliminated about half of them. I expended more energy than I do in the same time at Pilates! It was half the time I had available to spray the whole cemetery and was not ideal exercise for an old man like me. Worse I lost my sickle. It was presented to me two months later having been found parked on a gravestone.
It was exactly at that time that my helpers - the  newly formed team of enthusiastic cemetery  volunteers - came to my rescue. As pillars of the church and law abiding citizens they were horrified that their cemetery harboured this weed. With no word from me they banned it. Every plant was removed and certainly none flowered. If any balsam appeared this Spring I never saw it. I don’t expect I shall ever see it in the cemetery ever again.

Case study 2 - Seaton Ross Village Plot

Accompanied by another seed borne alien invader- buddleia
As a service to the village I killed a pure stand of two foot high ground elder ten years ago. There was no room for balsam which was completely absent. Perhaps I was breaking the law in creating  a refuge?
A ditch exists alongside the plot. It does not run - it has nowhere to go and is blocked at both ends! it meanders a few hundred metres but as a functioning ditch has been ruined by builders and householders. Perhaps it is they that should be prosecuted! Its like a long thin lake that only rises in very wet periods. Sure enough balsam invaded the newly vacant plot alongside the ditch bank.

Balsam now looks very pretty in a corner of the plot bounded by the road and confined ten metres away from any water by my own routine spraying. It is mixed in with other wild flowers and garden plants and looks very pretty. It is a haven for bumble bees. Perhaps when they read this villagers will have it confirmed I am a criminal. I will commune with the bees.
Last Winter was exceptionally wet and the ditch flooded again. It brought in plenty of featherlight seed of epilobium. (willowherb). The balsam remains snug in its corner and there is no evidence of balsam washed in.

Case study 3 Askham bog
Administered by Yorkshire Wildlife Trust it is the only alkaline fen in this part of the country. Peter’s friend Alistair, an international famed ecologist and plant science expert provides help and voluntary advice on its management. I understand that Himalayan balsam is now a problem. Peter offered to ask Alistair about it. Here is Alistair’s reply.
Peter
Yes, I think HB is one of the few invasive species that can be a real problem, especially in places such as Askham.  It can form monodominant stands and even out competes nettles, while the standard fen flora of things like water forget-me-not and skullcap are completely suppressed.  Of course it is only competitive where the early spring ground is more or less bare, so it tends to be mainly in woods and on riverbanks.

I increasingly see it well away from rivers where it is now probably the commonest riverside plant.  It is easily controlled of course, if you have the manpower, but the problem is that if you are on a watercourse it just reinvades from waterborne seed, as at the bottom of my garden.

There are a few upsides - it's a good nectar source late in the season and is pretty - but on the whole I'd rather see the back of it. That's wishful thinking of course as it's here to stay. I had a PhD student years ago looking at the root causes of invasiveness, using balsams as a test group. It's odd that the native spp should be so rare while several introduced spp are doing so well but invasiveness is very hard to predict.  
It is illuminating to read Alistair’s concerned yet relaxed approach.

Case Study 4 Pocklington Canal
I have chosen this example because it is not Invaded and I don’t know why!
The canal runs from Pocklington down to the river Derwent nine miles away. We have walked it all but not on the same occasion! The canal water levels are maintained using parallel balancing streams.
Not all the canal is navigable and it is maintained by enthusiastic volunteers financed by public donation. You can come to Melbourne and get a free ride on Sundays.
The river Derwent itself does support extensive balsam.
Considering balsam has been in the country longer than the canal has existed its absence alongside the canal is surprising.

Perhaps the reasons for its complete absence are
  • the well established existing vegetation such as reeds
  • in parts mown grass banks
  • zero tolerance by volunteers
  • that canal water levels do not change and their is no erosion to create eroded enbankments
Case Study 5 My own garden

This dwarf Himalayan balsam loves the margin of my pond

When we moved in to Boundary Cottage fifteen years ago we had an acre of garden to fill. For temporary flowers I sowed some ‘anonymous' seed mixtures! One of the seedlings was a dwarf form of Himalayan balsam. Its is a dead ringer for the real one and I have never seen any reliable reference to it. It is certainly not Impatiens balsamina, a known garden form.
Needless to say it comes back from seed every year and is now quite prolific - in a completely glyphosate controlled way. I ‘allow’ it as ground cover in a heavily shaded wet place in my garden where few other plants will grow. It is much admired by visitors.
I recently gave a lady some seed for her garden. I await an early morning knock on the door.


It grows in dense shade

Link to Askham bog web site



2 comments:

  1. I wonder what criteria they use for deciding whether a wild plant is desirable or not?
    We have Himalayan balsam growing along a strip of ground just outside our allotment along the fence. The strip is probably about a couple of feet wide. The plant doesn't seem to stray away from the strip which has hard ground to one side where the cars run backwards and forwards and tarmac to the other The council ignores it so they don't seem to be all that concerned.
    I thought all boys liked to play with machines.

    ReplyDelete
    Replies
    1. No it does not do well in tarmac Sue! (until someone reports it does). Seriously you have a good point that if it is confined by a few metres of unsuitable terrain it is restricted,
      Machines just stress me, especially when they don't work! As to the boy bit I am now in my second childhood.

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