Invasive or Invaluable – 10 plants that should come with a warning!

It’s true to say that I have to manage an impatient streak in my nature as it sees me adopting a quick impact strategy when planting even after many years of gardening. I am particularly mindful of my very early gardening days and the planting of houttuynia cordata in a long deep border – within a year it was popping up all over the place at an alarming distance from the original position. Or the sumach tree that suckered to a circumference of at least 2 metres and indeed continued to do so long after the tree was removed. Then of course there was the water mint mistake; a bee magnet if ever there was one and so it’s a worthy addition to the pond-side, but in a very secure, monitored pot! I planted several of them to cover an area quickly and guess what – it spread rampantly with frenetic speed along the border and into the lawn –  again, it took several years to completely eradicate.  

Looking out over the front garden, I’m having to acknowledge that the small clump of helianthus laetiflorus, a perennial sunflower I allowed to regrow last year has quadrupled in size and is clearly making an attempt on the whole flower bed. Originally planted some years ago, I started trying to eradicate it after a couple of seasons, as although really pretty and loved by bees, it really is a thug. Growing to a height of 4 feet and covered in pale yellow sunflowers in late summer, it certainly makes a statement but tight control is essential, which I seem to have failed miserably with!

Another plant I’ve tried hard to be rid of is euphorbia amiglioides ‘Robbiae’, to be admired with its acid yellow flowers and glossy leaves particularly when glistening under a light drizzle. I say admire, which is my immediate reaction, but really I should be asking myself why it’s there at all, as over the years I’ve made quite a few attempts to get rid of it!  This plant, for all its aesthetic attraction has an indefinite spread and as such it’s very easy to lose control of. I planted it originally with a small clump from my mom’s garden and it now pops up all over the place, clearly self seeding as well as utilising its very effective root creeping ability.   

Lysimachia ciliata ‘Firecracker’ – oh dear! A lovely plant for foliage, and it certainly forms a decent clump quickly, but to me it’s an absolute monster and seems to be impossible to eliminate. I planted a small clump in an extremely dry, free draining area of our garden (because I love its luscious colour), thinking it wouldn’t thrive and therefore be easy to control – think again, it ran wild and I took it out 2 years later. Unfortunately several years later, it is still emerging each spring. In Wales, the garden’s previous owner had planted ‘Firecracker’ near to the river bank, but it had spread far further than the 0.1-0.4 metres indicated on the RHS plant finder. When we attempted to reduce the clump’s size, we discovered the large bucket it had originally been planted in – which it had long escaped. This rogue continues to emerge all over that particular border, even through a broad, tough mound of hosta!

So – are there plants with these challenging habits that are worth keeping under control because of their value in the garden? Of course there are! In spring, I love the wild lungwort, pulmonaria officianalis, growing at the back of our pond – but it spreads quickly and indefinitely over the ground with gnarly dark and dusty stems. However, after flowering, it’s easy to regain control if you just leave a few small clumps for the following year – but I mustn’t forget, or the hellebores and anemones planted in the same area will be completely swamped!

Then there’s persicaria, two varieties in particular that I love, firstly persicaria bistorta ‘Superba’ (left). This plant has been living  around the pond for as long as I can remember – it’s a bit harder to control than the pulmonaria, but so worth it for its spring flowering – and cut back, it will flower again later in the year. Persicaria amplexicaulis ‘Firetail’ (bottom right) allegedly has a four foot spreading distance – but it just keeps advancing through the borders! It is useful in Wales though as it’s a great weed suppressant. I do regret the innocent looking persicaria capita (top right), it’s been in situ for two years and only this season has it revealed its true nature – popping up all over the bed with no thought for the other inhabitants – very reminiscent of the above mentioned houttuynia cordata, it’s just got to go!

Moving onto rampant self seeders, I love the easy self seeding alchemilla mollis, (it looks fabulous planted with potentilla ‘Miss Wilmot’ as above or geum ‘Mrs Bradshaw’) and hardy geraniums are a stalwart in my garden. But both need to be kept in check and unwanted seedlings removed when tiny or before you know it, there’s an invasion! Although I do love the hardy geranium pictured, it finds its way throughout the garden, as does geranium macrorrhizum, with its strongly perfumed leaves. 

Two lovely plants are to be found in catananche caerulea (‘Cupid’s Dart’) and Sisyrinchium striatum. Both are hardy and beautiful to look at, but both prolific self seeders, thankfully their seedlings are distinctive and easily removed, for if they were left in situ, this bed would contain just these two plants.

Finally, the magnificent crocosmia ‘Lucifer’ – it’s a wonderful plant and definitely ‘invaluable’ for the back of a border, but it has a broad spread and a habit of self seeding in the most unsuitable places for such a tall specimen!

I don’t have any confidence in my ability to control my ‘quick results’ impulsiveness because I have such an impatient temperament, but every mistake is a lesson and so I’ll just keep trying!