When good plants go rogue

I liked how the cutwork foliage provided a contrast to the dominant grassy foliage

It is no good. The plume poppy had to go from the sunny Court Garden. While I liked the foliage contrast, it is just waaaay too invasive to leave in place.

That is the full extent of the flowers. Pinky beige, perhaps?

The plume poppy is Macleaya cordata, native to China and Japan. It has an attractive blue-grey leaf that looks a bit like the plant version of cut-work embroidery. In spring and summer it shoots up stems to maybe two metres before flowering. True, the flowers are not exciting. More brown than gold, they look like seed heads even when they are in full bloom but they have a certain feathery charm while playing second fiddle to the more striking foliage. The problem is that it runs below ground, more like sprinting than running in some situations.

Here a fortnight ago, gone today on the grounds of bad behaviour

We have grown it for years in the high shade of the Avenue Gardens where it has not been problematic. The running tendency slows in shade – more a walking pace  – and in the thinner, dry soils it is easy to pull out wayward shoots and keep it to an area. I was not prepared for what it would do in cultivated soils in full sun. Not only did the runners bed down to a greater depth but they headed off with gusto in every direction, popping up metres away from the original plant.

Making a break for it

Really, it was the determination to colonise the paths that sealed the fate of this plant. Look at these runners appearing in the terrace. Not only have the shoots struck out enthusiastically on every side, this terrace is 30 cm higher than the garden bed, separated by a brick wall. I just don’t need a plant that can make such determined efforts to colonise. It was already growing through other perennials in the garden beds and leaping beyond.

It is going to take me a few years to completely eradicate it because roots that remain below ground will continue to push up growing shoots but I removed all that was visible two weeks ago and will just keep on its case until it finally disappears.

Macleaya cordata can remain quietly co-existing in the high shade of the Avenue Gardens

It can stay in the shade of the Avenue Gardens but I can’t be having invasive thugs in the Summer Gardens.

Phlomis russeliana flowering now in the shady Avenue Gardens where it will probably be fine left to its own devices for another decade or so.

Another plant that has surprised me with its vigour is Phlomis russeliana or Jersualem sage. While described as a perennial for sunny spots, we have long used it as a low maintenance, obliging bedding plant in the high shade of the Avenue Gardens. It has never needed any attention there, bar cutting the tall growth and spent seed heads back to the ground at some stage in winter. The only time I have ever done any work on lifting and dividing it was when I raided the patch to get plants for the new, herbaceous borders.

In the sunshine, the phlomis romps away and needs major attention every two years at least.

Introduced to the bright light of full sun and well-cultivated soils, the phlomis has become something of a triffid. The growth is lusher and much stronger. The twin borders are only entering their fifth summer but the blocks of phlomis have already been lifted and divided twice, discarding probably half of them in the process. I think I can get away with a total dig, divide and replant every second year if I alternate it with picking and thinning them from the top in the year between. It is a bit more work than I had anticipated for a cheerful but utility plant.  While it seeds a bit more in sunny conditions, at least it doesn’t spread below ground like the plume poppy.

The lines between a strong grower, a thug and an invasive weed are sometimes finer than we expect. Generally, we will cope with the first and get rid of those in the second two classes.

8 thoughts on “When good plants go rogue

  1. Tim Dutton

    Always a worry when you read about a potential thug, so I checked our Macleaya once more and it is looking anything but thuggish at the moment, still a single stem after 2 years and wobbling in the ground, so it can’t have a very good root system. The difference is that it is planted in extremely challenging ground that has never been worked, with almost no topsoil, heavy clay and stones. We find the same with the Phlomis, which we grow a lot of, and that too takes quite a long time to colonise the areas of poor ground, but it does a great job in those over time.

  2. robynkiltygardensnz

    Hi Abbie
    I have exactly the same problems in my small but intensive garden, and have often envied big gardens with the space to let things rip! But your story tells me not so! Just more space in which to romp!
    Shame that the thugs are often such attractive plants! I have had Macleaya cordata and I, too, liked the foliage, but it’s well gone now, only to be taken over by Stipa gigantea which I nursed along to begin with, but which is now overwhelming my front garden. I love it, but why does it have to grow so enormous? So it will get hacked back yet again this winter, along with the other attractive weed/thugs which inhabit my garden! Watch that Phlomis – mine had to go!!

    1. Abbie Jury Post author

      You may recall sending us a small division of Stipa gigantea? Yes, well, now I lift and divide all the stipas every second year (by all, I mean maybe 20 plus plants) and discard half of them. But at least it neither seeds nor suckers.

      1. robynkiltygardensnz

        It sounds like a huge job dividing 20 Stipa’s every second year – groan – groan. But I bet they look stunning in the garden! Just scanned your Xmas blog – it looks very artistic!!

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