August 2020: Acanthus spinosus

Acanthus spinosus is a statuesque statement plant for the back of the border. Well some think it’s a front-of-border plant but I’d suggest you don’t! It fits the description “tough as old boots”. Demanding little care beyond chopping down flower stalks once they’ve gone over and tidying up in spring, it can grow to more than a metre tall and around 60-90cm (2+ feet) across. In early summer, it produces strong, 100cm tall spikes of flowers. The flowers are white with purple bracts. No need to stake; sometimes a flower spike will decide to grow at an angle and you might want to put a cane in to hold it upright but make sure it’s a strong cane – that flower spike wanted to grow diagonally and you’ll have a fight on your hands to convince it otherwise!

Leaves are deeply cut and come armed with rather tough and very sharp spines. Painful if you’re not careful. And very painful in the front of the border when you brush past it.

Make sure you want it and make doubly sure that you plant it in the right spot. For once it establishes, you’ll never get rid of it as it develops a deep tap root over time and even if you have the energy to dig that deep, leave just a bit behind and it’ll regenerate.  Impervious to Glyphosate, it’ll recover from attack with a flamethrower and regrow the next year.

OK, so I didn’t practice what I preach! For the first few years in the garden, at the back of a 2-metre-deep border, it looked good. I was happy. But then, one year, it decided to do a runner! Well, lots of runners. Acanthus plants popped up all over the place. One appeared right at the front of the border; others right along the border, up to 2 metres away from the parent plant. OK, so it’s relatively easy to dig up the small plant, separate it from the running root, pot it up and flog it on to some unsuspecting neighbour. Well preferably not a neighbour; you want to be far enough away when they discover the downsides!

But that’s just the offspring dealt with. You still have that 2-metre running root from the parent. And if you don’t get that out, you’ll have lots more little plants popping up all along it. And getting that running root out will probably mean digging up all the plants that it’s running under, getting the root out and then replanting them. And you won’t just have one running root! The blasted things will be running out in all directions. There’s only one way to handle things now. Diligence.

Which is why, a couple of times a year, you’ll find me digging a trench around my parent plant to get out all the root shoots. I tried digging the parent out. Thought I’d got it all. But it came back the following year!

And even with this diligent approach, it’s come up again this year, right at the front of the border!


John Kingdon