Gardening: Invading Rhubarb

'A LEAF so large that you can use it as an umbrella to shelter from rain.' This was one of the claims made on the label attached to Giant rhubarb AKA Gunnera tinctoria back in the days when it was freely available for sale. What they forgot to mention was that this perennnial forms huge clumps and shades out other plants completely.Also known as Chilean rhubarb, Gunnera tinctoria, like many of our other invasive plants, began life in this country as an ornamental plant for gardens. Inevitably it got around to making a break for the wild through seed dispersal and the all too common but ill-advised dumping of its offcuts and overcrowded roots on pieces of waste ground. Through such propagation methods it has taken a firm hold within the sort of locations it prefers, namely soil-rich roadsides, waterways, damp meadows, and along coastal cliffs.No rhubarb tartsDespite the names common 'Giant rhubarb' and 'Chilean rhubarb', Gunnera tinctoria is not related to rhubarb at all (so no eating); instead this name alludes to their similar appearance when in leaf. Its 'umbrella' shaped leaves could be confused for ones of rhubarb I suppose if viewed from above, their broadness, puckering, visible veins, colouration, and shape being reasonably similar. However look at the leaf from beneath and you will see Gunnera's telltale spines all along the midrib of the leaf.Look closer and you will see that its sturdy stalks are also covered with these spines. All this is visible from spring onwards once Gunnera tinctoria emerges from its winter dieback, a rest period where conveniently its large leaves collapse down over the plant's crown, providing an effective frost cover. It was as if the plant was engineered to preserve itself no matter what, and to be fair most plants whether welcome or unwelcome have some coping devices equal to this.In a similar fashion to the invasive Giant Hogweed I wrote about recently, it is Giant rhubarb's size that is the main problem. Over spring and summer it can grow up to two metres tall, clumping as wide as it can with leaves that have the ability to span two metres across. With bulk like that it really competes for space, food, and sunlight with our native plants, natives that the vast majority of our insects rely on for food and shelter.At home in Co MayoIf you've never seen Giant rhubarb in the flesh, well then take a trip to Achill Island, Co Mayo, where it seems to have taken hold and has spread throughout. The west coast of Ireland appears to be its playground, our high annual rainfall and temperatures rarely falling below 0º C are just to its liking. Who would have thought we would have that much in common with the plant's native home of Chile.The main method of control employed by local authorities so far for Gunnera tinctoria has been chemical-based. Liberal dosings of Roundup (glyphosate) and Garlon (triclopyr) have shown fairly good results. However working this around waterways has obvious and far-reaching negative consequences beyond just the control of a clumping weed.As one gardener I know said 'The one thing Gunnera can't abide is the drought, how Irish'. There's truth in that, so it might just help if we got a few of those oft forecast but seldom realised scorching summers and prolonged heat waves. Weather such as this might save the county councils a fortune in herbicides.You will seldom see Giant rhubarb AKA Gunnera tinctoria for sale any more, but if you do see it available I'd steer well clear. I'd even go so far as to inspect any other plants you buy from its host nursery for rogue Gunnera seedlings, as you may inadvertently be bringing a little passenger home with you as well. Better to be safe than sorry.As with all the invasive species mentioned in previous columns, you can submit records and sightings of them on the invasivespeciesireland.com website. All records and sightings you can submit will help the relevant bodies determine the extent of the invasive species problem in Ireland and facilitate a rapid response, where necessary.Until next week, happy gardening and remember that a weed is just a plant in the wrong place.As well as his horticultural writing, James Kilkelly provides a garden and landscape design service. Contact him through his website www.gardenplansireland.com or alternatively by phone at 087-2067846. Visit www.irishgardeners.com, the Irish gardening resource.