Ground-cover plants are great ...but don’t let them go rogue
Vigorous plants that cover borders are a wonderful addition but, says our expert Agnes Stevenson, but choose carefully to avoid problems later
For as long as I can remember I’ve loved a “good do-er”. I’ve been passionate about those plants you just stick in the ground and watch as they romp away. While others shy away from growing Forget-me-nots and Grape Hyacinths because of their tendency to run, I’ve planted them in the hope they would cover the soil, confident I could evict them from places they become too vigorous. After a slow start, the lime green Wood Spurge (Euphorbia amygdaloides) is racing across the border beside the drive and already the first leaves are appearing on the Lady’s Mantle that flings its seeds around the garden and then pops up everywhere, producing clouds of acid yellow flowers. Now, though, I’m having to rethink this casual approach to ground cover after, for many weeks, waging war on an innocent-looking flower that, in my garden, has gone rogue. Persicaria bistorta, or Common Bistort as it is often known, is one of those plants that seems inoffensive when you first plant it. I’ve grown it now in several gardens and I’ve given away divisions to family and friends and in all cases it has been a pretty and well-behaved addition. Two years ago I introduced it to my current garden and, by last summer, I began to suspect I had a problem on my hands. Not only were the individual plants clumping-up rapidly, but seedlings were appearing all over the borders. And, when I tried to remove them, I discovered they had developed deep tap roots that went down much further than I could reach with a spade. Removing these and the long rhizomatous threads that join individual roots together is an on-going battle and my spirits dipped when I did
some background research and discovered my problem plant belongs to the same family as Japanese knotweed – the big daddy of all invasive species. The reason the Bistort has run amok in my garden is all down to heavy, rich and permanently moist soil. In drier, less nutrient-dense ground it behaves nicely, sending up spikes of pink bottle-brush shaped flowers in early summer without any attempt to colonise the entire garden.
So far I’ve dug over half of the border and filled an entire brown bin with pernicious roots. I’ve also uncovered an infestation of vine weevil larvae, which will need to be treated with nematodes once the soil warms up.
Most plants don’t survive close contact with vine weevil grubs but it seems Bistort is impervious to them...and just about everything else as well. In fact the Royal Horticultural Society lists it as “pest and disease-free”, a description that fills me with dread as it seems that there is nothing that will stop it in its tracks.
For now I’ll keep digging and if it comes back, I may have to resort to a glyphosate-based weedkiller to keep it at bay.