@NormandyLiz Yes they do spread by runners. One we have in a border has spread so much that we have had to keep digging up what we can find as it was taking over the area. The same plant also spread underneath a beech hedge (still in our garden) and established itself on the other side. This we have left alone as it isn't crowding out other plants. We do still like the plant so the "new" one will stay.
In poor, well drained soil it will flower well and be beautiful and not too invasive.
In softer, richer soil you're likely to get lots of foliage and not as many flowers so pick your planting site well and you should be OK.
I planted a couple in tow beds in my Belgian garden but it was rich, fertile soil and we had lots of rain so all I ever got was healthy foliage. I decided to dig up both of them but their roots do go deep and re-grow. I dug them out every spring for several years before they gave up. Neighbours, 800m away and on poor, sandy soil, had beautidul blooms and no thugs.
Vendée - 20kms from Atlantic coast.
"The price good men (and women) pay for indifference to public affairs is to be ruled by evil men (and women)."
We have poor, sandy soil and it grows well here and flowered ok but it regularly looked absolutely awful due to powdery mildew before I took it out. I swapped it for some echinops which are much easier to deal with and cause no trouble apart from weeding out the volunteers. The acanthus seeded prolofically and I can see why some might find it invasive but for us it was never much of a problem. It does come back from any part of the roots you leave behind so you need to repeatedly deal with them until it's gone.
Acanthus drop seed which germinate fairly easily and when they re in the wrong place they are a nightmare to remove. The tiniest bit of root left starts again. I wouldn't plant it again.
What's fascinating is how many different thoughts there are on one plant, or even just one aspect of it. Which may explain why different websites say different things.
Just to add the confusion, I have several in the garden and have moved a couple of established plants as well. It doesn’t seem to care if it is in sun or shade, it does rather well and throws up several flower spikes on each plant. I have heavy, rich clay soil. Only in one bed has it developed runners and I just have kept pulling them up. Couple of years later, the parent plant is still in place but no more runners from the roots.
No don’t do it! They are very hardy and indestructible. The problem comes once they have grown too large and you want to move it. The roots are so deep it’s just impossible to Totally remove. It keeps popping up in different parts of the bed, and no matter how hard I try to remove It I can’t.
Thanks, @LilyW. I am going to do it, but 'safely'. I've got a very large pot with drainage holes that will be covered with a layer of very fine holed plastic mesh (1mm holes) to stop roots getting through. As Nollie suggested, I'll then lift and check from time.
Given I've germinated the seeds and I do love the plant, I just can't bring myself to throw them all away! I'm only keeping one, though. 2 will be given to friends who are very aware of the problems but would still like one, and one is going to a charity garden, again they know it's 'challenges'.
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In softer, richer soil you're likely to get lots of foliage and not as many flowers so pick your planting site well and you should be OK.
I planted a couple in tow beds in my Belgian garden but it was rich, fertile soil and we had lots of rain so all I ever got was healthy foliage. I decided to dig up both of them but their roots do go deep and re-grow. I dug them out every spring for several years before they gave up. Neighbours, 800m away and on poor, sandy soil, had beautidul blooms and no thugs.
Only in one bed has it developed runners and I just have kept pulling them up. Couple of years later, the parent plant is still in place but no more runners from the roots.
Given I've germinated the seeds and I do love the plant, I just can't bring myself to throw them all away! I'm only keeping one, though. 2 will be given to friends who are very aware of the problems but would still like one, and one is going to a charity garden, again they know it's 'challenges'.