Enemy at the gates
When an unwise purchase threatens to overrun a border, Frank decides it is time to arm himself with a fork and take back control
Columnist Frank Ronan comes to regret planting a Persicaria wallichii
Sometime back in the 1980s I got a whiff of something nice in Beth Chatto’s garden and, eventually, tracked it down to a giant bistort with panicles of creamy white flowers. It went on the mental long list of plants I would one day grow if I got my hands on rolling acres. Cut to fifteen years later and the acquisition of this mildly sloping third of an acre and the excitement of a new garden and wanting to plant everything that had ever caught my eye or nose, no matter how unsuitable, unwise or uncontrollable. Persicaria wallichii came to join us.
I was not entirely incautious. It was planted at the back of the long border, with small trees either side to hem it in. When it began to demonstrate territorial ambitions I took advice and made a barrier at the furthest extent I was prepared to allow it. My advisor put me on to 450mm damp-proof membrane, which he said was strong enough to hold a bamboo back. A semicircular trench was dug and the subterranean wall installed, and I walked away looking forward to many years of happy coexistence.
Which, to some extent, we had. The bistort, on reaching the barrier, milled about not unlike a horde at the frontier and soon, inevitably, began to pour over it. Those incursions were easily patrolled by regular slashings with a sharp spade. More tiresomely it began to poke up through the concrete access path at the back of the border, making regular strimming a necessity. Most worryingly it would pop up in random places in the border. Extracting those pieces involved serious delving and disturbance of other plants, and I began to think I had made a horrible mistake.
The worse its behaviour became the less alluring the scent seemed and the coarser the flowers and leaves began to appear. I thought sometimes of having the whole lot out, but the more it grew and the more daunting the task became the more easy it was to convince myself that I had the situation under control. And before I went to America I did manage to keep on top of it, more or less.
You can imagine what three years without discipline did. I could see now why some people call it Himalayan knotweed. That whole border needed an overhaul, but the couch and hogweed and bindweed elsewhere seemed positively benign compared to this intrusive guest. The paralysis of not knowing where to begin the restoration, not helped by the least gardening-friendly spring in living memory, was soon overcome with the realisation that one should always get stuck in at the most horrible part of a job. The thought of starting at one end of the border while the knotweed advanced brazenly to meet me was too much. I attacked it at the source.
I had forgotten the satisfaction of long days kneeling in waterproof trousers, digging deep with a fork and fingering through every handful of soil for stray bits of unwanted root. That was how that whole border was made to begin with. Only this time I had the encouragement of seeing the benefits of my own handiwork as I went. The crumbling gritty texture; the lost treasures rediscovered and carefully rescued, potted up and put to one side for better times to come; the knowledge acquired since of what would like to grow exactly where, allowing sound plans to replace fantasies.
I know that, for years to come, the knotweed beast will recrudesce and regroup. With that in mind the plan is to use that part of the border for dahlias and cannas and summer bedding, so that twice a year it will all be dug up again and every remaining trace of the bistort hunted down and deported. It is long since I had such scope for dahlias, not to mention zinnias and cleomes and sunflowers, and I can’t think of a nicer way to clean the ground. It is the ultimate win-win situation.
THE BISTORT MILLED ABOUT, NOT UNLIKE A HORDE AT THE FRONTIER, AND SOON BEGAN TO POUR OVER IT