There are many evergreen ground covers for the shade garden, but not so many that are tough, vigorous and capable of covering large areas quickly. Behold the English ivy, a woody vine that has entwined itself into history, myth and the carport.
Once routinely planted in the poshest gardens in the land, including the White House, and fashioned into wreaths by the Greek gods, the ivy has fallen on hard times.
Ivy was invaluable when gardens were more static, tidy and architectural, but it was eclipsed by more interesting ground covers by the end of the 20th century. Thus ignored, it decided to make mischief.
Untended for long enough, the ivy will clamber to the top of a tree and from its high perch transform itself into an evil twin. Aloft, its distinctive foliage shifts to a paddle shape. In the autumn, the clusters of little white flowers draw bees from afar and then spend the winter turning into black berries. Birds devour them and spread them into the wild. Thus seeded, the ivy begins its patient journey of conquest. In Rock Creek Park, it has been spreading for years, though the invasion is being pushed back. Since 2013, volunteers with the Rock Creek Conservancy have pulled ivy vines from 12,687 trees, most of them in the District.
This is done by cutting the vines that cling to the trunk at shoulder level and at ground level, using pruning saws and loppers. Often the severed segments have to be pried, carefully, from the tree using a crowbar, said program manager John Maleri.
You can (and should) do this at home, but don’t rip down the vines immediately. They take a few weeks to die and wither, and it then takes a hard freeze to get the aerial roots to release their grip. At that point the vines either fall or can be tugged down without harming the tree.
Most of the conservancy’s effort so far has been in removing the fruitful vines from trees rather than as a ground cover, though the trees are kept clear of encroaching vines.
What is the problem with English ivy in natural areas? On trees, the sheer mass of the vines can help bring down the host in storms. Ivy also blocks sunlight that trees need to feed. Aesthetically, it’s hard to love the look of a tree cloaked in ivy, unless you’re into Gothic horror.
On the ground, the ivy suppresses indigenous woodland plants, including such spring beauties as trilliums, May apples and Virginia bluebells. And for people who want their landscapes to consist of native flora, it’s simply a bullying invader. This is a contemporary viewpoint, as English ivy was once considered an elegant element in American gardens that looked to English and European garden traditions.
Rock Creek Park is an example of a natural area at high risk of invasive exotic plants once used commonly as garden staples, because the park is close to hundreds of homes. “A lot of areas we are working in, you can look across the street and see the ivy growing up somebody’s hill. All the trees on the property have vines growing up,” Maleri said. “It’s very apparent where the ivy is coming from.”
When the Dumbarton Oaks estate in north Georgetown was given to Harvard University, the owners donated the outlying 27 acres to the National Park Service. In recent years, the Dumbarton Oaks Park Conservancy has been battling to reverse decades of neglect of what was designed as a romantic, naturalized hinterland of the mansion.
One of the problems facing the conservancy has been that the landscape architect, Beatrix Farrand, freely planted English ivy, which then made its way to the wooded stream valley that is the park.
From a one-acre section called the beech grove, volunteers over the past five years have removed carpets of ivy, tallying at one point a total of 600 50-gallon bags, said Ann Aldrich, the organization’s invasive plant management specialist. They have also pulled ivy from several hundred trees as well as mature rhododendrons. Although they’ve made headway, “there is a lot of ivy left,” said Lindsey Milstein, the conservancy’s president.
Maleri’s group has been able “to educate park users to steer them away from English ivy. The less people plant it, the less of an issue in the park down the road,” he said. Ivy is listed as a noxious weed in the Pacific Northwest, where its sale has been restricted.
If you have ivy as a ground cover, the simple act of keeping it in bounds with occasional clipping will stop it from spreading. On a wall or fence, the same maintenance approach will work. If it is growing up a tree, remove it.
In spite of ivy’s environmental risks, there are some gardeners who feel ivy still has a place in certain situations and can be used without creating a problem. I’m inclined to agree. There are certain variegated varieties in particular that can brighten a wall or pillar in a gloomy corner where little else will grow.
These tend to be slower-growing and more tender than green types and, if kept in check, don’t present an environmental threat. One of them, a variety of Algerian ivy named Gloire de Marengo, is particularly handsome, appearing splashed in a tapestry of green, silver and cream. The English landscape designer Russell Page once installed it in the French garden of the Duke of Windsor, the erstwhile King Edward VIII. Page liked how such variegated ivy on a dark wall “will give the effect of dappled sunlight.” He did counsel pulling ivy off trees, however. Finding a source for it might be difficult, along with other once-common varieties now hard to find as growers have retreated from the market. Classic variegated varieties include Gold Heart, Buttercup, Goldchild and Gold Baby.
Tony Avent, owner of Plant Delights Nursery in Raleigh, N.C., used to sell ivy but stopped, not because of its ecological issues but because it was a bully in the garden. Still, he thinks ivy is "fantastic" in the right setting. "It's all about how it's used and how it's managed," he said. However, he can think of many alternatives for the shade garden, including evergreen ferns, wild gingers, hellebores, mondo grass, a little-known evergreen shrub named ruscus, and the native partridge berry.
Ivies are effective trailing plants in containers and baskets in shady patios and can be used in winter pots along with such things as boxwood, pansies and dwarf conifers. In such a setting, the ivy would not get out of hand.
Perhaps this is passe as well, but ivies can be grown on wire forms to produce topiaries. These are still a feature of the competitive classes at the Philadelphia Flower Show, but the Philadelphia chapter of the American Ivy Society no longer stages a display. "We still award a ribbon at the show, but we don't have the presence we once had," said ivy fancier Russell Windle, of Media, Pa.
Costa Farms, a major wholesale grower of houseplants, has a broad range of ivies designed for use indoors, though many are hardy in the Mid-Atlantic and would work as outdoor container plantings. Some gardeners treat them as seasonal plants, removing them from containers in the fall and overwintering them indoors, said Justin Hancock, a horticulturist for Costa Farms in Miami.
Ivy may continue to be an active part of greenhouse gardening, and it will stick around as a ground cover in established gardens. In the realm of contemporary horticulture, though, ivy has lost its mojo. But a future without ivy? Unlikely.
“We’ll probably be battling ivy forever,” said Liza Gilbert, of the Dumbarton Oaks Park Conservancy.
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