Blog: do you put up with them or eliminate plants that smother everything?
With the news that Gunnera is now banned in the UK, which are the worst invasive plants to avoid in your garden? Here, I’m looking at the real bully boys who will out-compete everything else, smother others and prove difficult to remove.
Like most gardeners, I’ve fallen in love with varieties in garden centres or glossy catalogues, only to rue the decision later. Here is my rogue’s gallery:
Invasive plants – Green alkanet (Pentaglottis sempervirens)
My public enemy number 1! I bought it at a local nursery and was told it was dyer’s alkanet (Alkanna tinctoria). I was swept away by the romance of producing homemade dye and bought one plant. However, it was green alkanet, which can produce a weak dye from its root. That’s where the problem lies – its deep, brittle taproot makes it difficult to dig up. It will also self-seed everywhere – my poor leek bed stands as photographic evidence.
It’s not much of a looker, with small, bright blue flowers similar to forget-me-nots, borage or Brunnera. The leaves are green and similar to comfrey. Stick to its more well-behaved relative Pulmonaria (lungwort).
How to get rid of it: Dig up plants, removing as much of the taproot as possible. Wear gloves as leaves can cause skin rashes. Don’t add freshly dug-up plants to the compost heap. Remove seedlings as soon as you see them. Keep digging up growth from snapped taproots until the ground is clear.
Ivy (Hedera spp.)
Probably the best-known name on this list, ivy can be a rampant pest but I still give it garden room. Why? It’s because it is so valuable to wildlife. Vertical stems flower in autumn, providing valuable nectar to pollinators. The black fruit is a favourite of some garden birds and large specimens provide good nest sites.
Ivy grows rapidly – growing less vigorous variegated varieties is one way around this. However, always check the expected size before you buy. Stems root readily when they touch the soil and seeds passing through birds will spread plants around too.
How to get rid of it: I don’t advocate the use of weedkillers and trim any ivy that’s becoming invasive. On trees or walls, cut stems to the ground and dig the stump out. If you can’t get to the stump, regular cutting of the stems to ground level will weaken the plant. If plants are purely ground cover, dig up stems and woody roots. You can also clear all top growth, then cover with weed-control fabric covered with a 15cm layer of mulch. Leave in place for at least two years.
Invasive plants – Acanthus mollis (bear’s breeches)
This is a plant I love and put up with its bully-boy tendencies. With its beautiful, glossy, large green leaves and striking and unusual flowers, it is an integral part of my front garden. The leaves are the inspiration behind the Greek Corinthian columns. Although plants don’t like wet, cold soils, any other condition will cause rampant growth, smothering other plants under a dense canopy of leaves.
How to get rid of it: Once the thick, fleshy roots gain traction, you’re fighting a losing battle. Like alkanet, they break easily and can resprout from the smallest fragments. Digging it out can make matters worse. Try cutting it back to the ground repeatedly. This will eventually weaken and kill the plant.
Of course, these are the plants that affect me. You can read more about serious offenders like Japanese knotweed. CEL Solicitors has an excellent post on invasive plants and the law in the UK – celsolicitors.co.uk.
Invasive plants – which bullies take over your garden? updated 2025
