English Ivy: Coming to a woods near you

This is an article I wrote for the January issue of the Parkwood Inside/Out, serving the Parkwood community, next to Northeast Creek in southern Durham.

English Ivy: Coming to a woods near you

Now that Parkwood’s green areas are bare, the full extent of the English ivy problem is plain to see. In places behind Newhall, Euclid, Revere, and between Highway 54 and Euclid ivy thickly covers the ground, smothering native vegetation, including the next generation of canopy trees, creating what might best be called “ivy deserts.” A few native and non-native plants do sprout through the ivy, including poison ivy, but the spring beauties, trout lilies, bluets, pink wood sorrel, pussytoes, and other flowers and forbs that should gild the forest floor are excluded. Ivy might affect invertebrates living in streams flowing through an ivy-filled woodland and change the soil, because ivy has nitrogen-rich leaves, a vital plant nutrient. It can carry bacterial leaf scorch, which infects trees such as maples, elms, and oaks. Ivy vines thickly festoon trees, which might make them more likely to fall, though there is some controversy, and less able to get to sunlight.

Once in the canopy, ivy gets enough sun to flower and produce clusters of black fruits, which birds spread into new areas. In my yard there is some ivy kept under control in pots, but in the last 10 years a lot of ivy has crept in through seeding. Without pests or diseases, cold weather is probably the main factor limiting ivy here, by preventing fruit production and temporarily stopping photosynthesis, an advantage evergreen ivy has over deciduous plants. For this reason, ivy is not a major problem further north, but it is rampant in the Pacific Northwest.

As its name suggests, common or English ivy (Hedera helix) is native to the continent of Europe, as well as the Middle East and north Africa, but it was introduced here starting in the 18th century. In its native range it is kept in check and is a valuable food source for birds, some of the species that have become problematic introductions here, such as European starlings and house sparrows.

English ivy is in the same family as ginseng, so it is not a relative of poison ivy or Virginia creeper (in the cashew and grape families, respectively), but I thought it was related when I took a large cut stem and pressed it to my wrist to see what would happen, and my skin blistered, but less intensely than it would with poison ivy. I’m pretty sure it was an ivy stem, and not Virginia creeper, and some people do react to ivy, but from a different toxin than that in poison ivy.

Ivy has evergreen, palm-shaped leaves with three to five points in shade, but they become more lance-shaped in the sunny treetops. The vines appear hairy because of glue-producing roots, while vines high in the treetops lack roots. Stems can be almost a foot wide, and reportedly a 433 year old vine in Europe was more than 20” across. Ivy has tiny and inconspicuous yellowish flowers that appeal to insects with a short proboscis, such as flies, wasps, and moths. The resulting fruit, technically called a drupe, contains a few hard seeds and a toxic glycoside that sickens humans and can make birds vomit. Still, the fruits are nutritious and fatty, and are often eaten by robins, mockingbirds, and cedar waxwings. As with some other non-native plants, human disturbances, such as new roads, give ivy inroads into new areas. There is a lot of ivy in Parkwood now, but it is rare or nonexistent in intact woods nearby. Livestock and deer can apparently eat the leaves, but don’t appear to be making much of a dent in the problem. Non-native rats might be the main animal that can use an ivy desert.

Other than landscaping, people have used ivy for its antifungal and antibacterial properties and in dyeing, tanning, and varnish resin.

Controlling English ivy and other non-native plants is a good New Year’s resolution. Many non-natives can be grown without causing too much trouble for native vegetation and the neighbors. There are more controllable non-natives, such as the groundcovers Vinca minor and Vinca major (they are similar, but V. major is larger and possibly more difficult to keep in check), which only spread vegetatively, but they spread a lot in shade. There are also many native alternatives. Crossvine is an evergreen vine with showy spring flowers that attract hummingbirds. Yellow jessamine is also evergreen and showy. Virginia creeper is a pretty deciduous vine with red fall foliage and dark blue berries. There are several evergreen groundcovers, such as doghobble, Galax, and partridgeberries (common in Parkwood).

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