Last week’s column on “why do nurseries sell this plant?” struck a chord with many readers as well as with Holly! So here is this week’s submission: that ubiquitous vine, English ivy.
First of all, we’ll stipulate than many ivies are sold as English ivy (Hedera helix) but may be entirely different species. Genetic research on invasive ivy populations in the Pacific Northwest identify most as H. hibernica (aka Atlantic ivy), with H. helix making up only 15% of the invading populations. Regardless of their species identity, it’s obvious that Hedera is a genus with the potential to escape gardens and invade remnant forests or other environmentally sensitive areas. It grows so vigorously that it can create monocultural mats on forest floors; it grows into trees where its sheer weight can break limbs and in some cases topple entire trees.
But what about other regions of the country – or the world, for that matter? In colder climates, Hedera spp. are much better behaved, dying back to the ground every winter and rarely able to flower and reproduce. The absence of a seed bank means the vine can be kept in check more easily. And it does tolerate tough environmental conditions where other groundcovers might not succeed.
Yet consider another invasive: kudzu (Pueraria montana var. lobata) For decades this noxious weed was thought to be too cold sensitive to expand past the American Southeast. Yet populations have been found in Maine, Oregon, and most recently in Ontario, Canada. Plants adapt!
So – is it worth the risk to buy a plant known to be invasive elsewhere, simply because it’s not a problem yet?
And why oh why do nurseries in Washington state continue to sell Hedera spp. as ornamentals?