Friday, 9 October 2015

Invasive Species — Of Couch Grass, Himalayan Balsam, and Signal Crayfish

There's an allotment society down Cubbington Road. I used to hold one many years ago. At the southern end is where you'll find spare plots up for grabs. Going spare because they are overgrown with couch grass. Let's give one to an experienced and wise old gardener and that adjacent to a rather hot-headed young man, eager to learn, but new to the game. See who wins out...

The old guy diligently loosens the grass at the root with a fork then pulls up the clumps and leaves them on the ground to dry. After a day's back-breaking work he's grubbed up about ten square yards, if that. The newbie brings in a strimmer, cuts it all back by noon, and fills his plastic compost bins to their brims. He then brings in his pride and joy. A second-hand petrol fuelled rotovator he'd purchased along with the strimmer from an old lady gardener just down the road from home, and turns over the entire plot in the afternoon.  In just one day he has a plot to seed, but the old boy looks something of a loser.

However, one knows something the other doesn't...

By the end of winter the old boy has finally cleaned his plot and then begins sowing potatoes end to end. As he digs and heaps the soil into ridges he turns in the dried clumps with dead roots attached, removes those many stray live plants and broken roots that he finds, and leaves them on the ridge peaks to dry in the sun. 

The newbie already has sown half or more with every classic vegetable in the rack and is now hell bent on seeding the rest with what exotics he can find online. He's also ladled on the fertilizer. And bought himself a shiny and very sharp stainless steel spade. There's rather a lot of fresh grass shoots arising, he notices. But then he goes away for a fortnight thinking his seedlings will thrive in his absence. On his return he finds his plot a field of lush light green and his seedlings smothered.  

The potato shoots emerge through the dried roots and soon the old boy's plot is also a sea of green. But it's the dark green of success because when the vigorous spud plants shoot up and outward they smother what grass emerges. He doesn't even bother to pull up what does break through the dense cover and thrive. Job done he surveys the scene, goes home, and leaves the crop to its own devices till harvest time. 

The newbie struggles to contain things only able to return weekends. When he hoes it in, it makes no long term difference. The bloody stuff returns and worse, his seedlings are not exactly thriving amongst it. By midsummer he is involved in trench warfare. Harvest time comes around and he picks what he can. 

The old guy returns only during protracted dry spells knowing his spuds will last through wet spells but get a little blighted. He doesn't care. He didn't plant them for the purposes of his own sustenance. Turning over his rows one by one, removing what grass roots he finds and laying them on the ground to dry in the sun and wind. he slowly harvests the crop. But taking all the wilted potato haulm and grass stalks to his properly constructed compost heap made of old pallets where he mixes both together and spreads them between alternate layers of soil. 

The crop isn't a heavy one without an application of fertiliser in springtime and plenty of grass having competed with it, but he knew that would be the case. When the job is done he looks at his nicely conditioned crumbly soil and leaves it for a fortnight. When he returns he plucks what grass shoots emerged meanwhile, root and all, and puts them in a bucket. And then he gets his fork and turns over the entire plot in a day and leaves it as rough chunks for the sun to bake and the coming frosts to break down further. What roots he finds he lays on the surface to dry and the bucket load is spread too. 

The newbie returns with his bargain rotovator thinking the old boy a martyr to hard work digging always with a fork and nothing more efficient. And a fool too, because he always leaves such an untidy mess of straggly roots behind him! He turns his entire plot over in an hour vowing to smash the damned grass to smithereens...

Both leave the plots alone throughout wintertime but spring comes around once more and the two plots are entirely different things. Both have grown plenty of clumps of grass meanwhile, but one is a clump here and there while the other is smothered end to end.

They set back to work... 

Three years on the old boy's plot is a thriving one — almost, but not quite cleared of couch grass. The entire volume of which and the essential nutrients contained therein, all returned to the soil without loss. He's also laid old paving slabs and patio paviours he's found in household skips. Not flat for pathways. But vertically and all around the perimeter of the plot with just the top edges showing above ground without gaps between. 

The newbie however, has been actively pulling up grass clumps, roots and all, and putting them in his plastic compost bin with all kinds of other random stuff. And then when it looks half done spreading it back on the soil and digging it in where surely worms will eat what wasn't composted. But still the grass grows and he's losing the battle. 

He doesn't know something the other does...

At harvest time he throws in the towel, picks what he can, and sells his rotovator and strimmer to the old boy for a pittance, who takes them home and puts them outside the house with a 'For Sale" sign attached.

Couch grass is not an invasive species unless in the microcosm of an allotment. But like balsam and crayfish the rhizome seems almost indestructible. Will easily survive the lukewarm heat of a badly made compost heap and chopped into a hundred pieces by rotovator, spade and hoe, will throw up exactly one hundred new offspring who'll lace the underground with yet more well developed rhizomes should they be left to grow. There is no easy cure except by thorough drying or soaking the soil in Paraquat, which is hardly a good idea on an allotment.

Himalayan Balsam is similarly equipped to survive the best efforts of all but the cleverest to defeat it. Each year well-meaning people go out on early summer 'balsam bashing' parties, where they fail to make the slightest dent in its armour. Like the newbie either they don't understand the plant they tackle or haven't the stomach for protracted systematic warfare.

There is a way to control balsam cheaply and effectively and without knock-on environmental damage to sensitive biosystems.  I'm surprised that no-one has yet thought of it. None of that grubbing them up by the root necessary. That's needless time consuming work when the plant is an annual and utterly reliant on seed dispersal for regeneration. You supply your band of workers with hedge trimmers, toodle along to the riverbank with picnic hampers, and enjoy a relaxing late summer social cutting off the flower sprays and underdeveloped seed heads. And then you don your waders and do the same in the water. 

Nothing to do after that. No removal of debris. No mulching down of remains and all that nonsense. Just leave the scene of decapitated stalks behind and break open the hampers!

You don't have to be 100% successful in removing each and every flower and seed head, each and every year. You won't achieve anywhere near that — just a few missed seed heads will easily repopulate when mature and explode shooting seeds up to twenty feet distant. This is a war of attrition. You do have to be 100% diligent. The practice must take place 'annually' when the plant is at its weakest having spent almost all its energy making young seed. And for years to come because mature seed remains viable for two years. Soon the colony will be weakened, then contained, and in time will be utterly eradicated.

And then severe outbreaks caused by negligence are simple to rectify — fine those who fail to keep their riverbanks in good order. Nothing ensures due diligence like an 'annually' emptied pocket.

Signal crayfish are a rather different prospect. It is not possible to cut their nads off. Well, it is. X-ray techniques can be used to sterilise males to be returned en-masse to the watercourse to impregnate fertile females. But not on the scale we require. 

God made crayfish with claws that cannot rotate 360 degrees to ensure they couldn't eat their own arses. I'm sure they would if they could because they will eat anything remotely edible. It has to be their downfall. Bait trapping is the way forward. But not with those little net traps that require someone return each and every day. But with big floating holding tanks cunningly designed to attract and keep them by the thousand. 

I'd propose twinned tanks with different sized entrances and with no way out once in. One is for immature specimens, the other for sexy full-grown ones. You remove the weekly catch from the small specimen tank, destroy them all but re-bait the traps with a few handfuls of well crushed corpses.

Those in the large specimen tank must be sexed, the females destroyed, but the big aggressive males all returned. Then you tow the tanks elsewhere and moor them for a week. And do this again, and again. When the whole stretch is completed, you make your return to point one and start over.

As time goes by the watercourse will become overburdened with males and under populated with females. The net result is going to be a disaster for the entire population because those many large males, but fewer and fewer smaller females, will surely eat their ever dwindling annual recruitment and when they run that supply down, will turn on each other.  

The boys will win that last desperate skirmish. The girls won't stand a chance against their superior size and reach. But it will be a pyrrhic victory for them.

If you don't tackle the root of the problem and tackle it wisely and diligently, you'll seem to win every battle, but will surely lose the war. 


  1. You're just trying to get my blood boiling Mr Hatt!

    And its working

    Where has all the common sense formerly passed between generations gone?

  2. In the wrong kind of compost heap I reckon, George!