Not so great escape Invasive foreign plants can play havoc if we let them

INVASIVE plants are often good ideas gone wrong. Always looking for new and unusual plants for the garden, we’ve been importing them from all over the world, especially during the 19th century. We now have around 70,000 garden plants, so it’s hardly surprising that some have

‘escaped’ to the countryside or the coast. Birds and the wind have spread seeds. Small long-tailed animals have squirrelled them away and forgotten where they were stashed. But many gardeners also dumped unwanted plants, without realising or caring about the damage they were doing.

So what, does it matter? Yes and no. It’s certainly risky. Do I need to whisper more than Japanese knotweed or Rhododendron ponticum?

And what about water garden plants choking waterways.

Scottish Natural Heritage, now strangely rebranded nature.scot, has described American skunk cabbage, Lysichiton americanus, as a dangerous threat to the environment.

Many other ‘garden escapees’ are less dangerous. They may not be robust enough to survive without our care and attention. But they could also do very nicely and outcompete more diffident natives, just as the Spanish bluebell could threaten the existence of our native bluebells.

This competition is a perfectly natural process that has always gone on. And with climate change it’s likely to accelerate. It’s not always clear when a garden escapee becomes an invasive alien.

The line between native and cultivated plants can be fuzzy. What I imagine are Welsh poppies generously spreading their delightful little yellow flowers around, aren’t actually Welsh poppies, Papaver cambricum. Real Welsh poppies thrive but don’t spread from a very restricted part of Merioneth.

What we call Welsh poppy is a much more dominant modern cultivar. Though a member of the same species it is not genetically identical to the modest native.

Like the Spanish ‘Welsh’ poppy, many plants new to Scotland may spread vigorously beyond as well as in our gardens. But it may take many years for them to become a serious threat.

Twas ever thus. Creeping bellflower Campanula rapunculoides was first introduced to gardens in England around 1568. It took a further 150 years before it was first identified in the countryside but is now widespread in Ayrshire and from the Lothians to Aberdeenshire. The originals were almost certainly dumped by gardeners.

And that’s the crux of it. We naturally can and should grow plants that thrive and appeal to us, but we should never dump them.

Alchemilla mollis, lady’s mantle, is an attractive specimen badly in need of control. This low-growing perennial with delightful pale green foliage and yellow flower clusters thrives where many goodies would yield to docks and willow herb. I’ve got one such bank where alchemilla beats the baddies.

Alchemilla does spread by seed, I removed one in the fruitcage the other day, but its seed doesn’t travel far. The rhizomes are different: once established, there’s no holding them back. As with so many dumped invasives, this takes time. Seventy five years after its introduction as a garden plant in 1874, lady’s mantle was found spreading in lowland parts of Scotland and even at 520 metres just below the summit of Ben Lawers in Perthshire. So always compost carefully.

It is difficult if the seed of a favourite is widely dispersed.

The Himalayan honeysuckle, Leycesteria formosa, is a case in point. Seventy years after its introduction in 1824, it began spreading and is now found along the coasts of the Lothians, Fife and the west.

So seemingly innocuous plants can eventually become problematic. A citizen science project invites gardeners to report any of their plants that spread unusually vigorously, so these nation-wide returns may pinpoint future invasives. Visit https:// plantalert.org

Lady’s mantle has been found just below the summit of Ben Lawers