The ‘Ivy League’ look is unhealthy for your trees!

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by Jay Watson, Co-Executive Director, New Jersey Conservation Foundation

While out walking or driving, did you ever notice trees so covered with ivy that they look like totally different life forms? In a way they are – because if the ivy continues to grow unchecked, the trees themselves might not live much longer.

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Trees laden with ivy are something I’m seeing more and more on my travels around this state we’re in. The colonizer appears to be English ivy or Common ivy (Hedera helix), an evergreen vine with waxy, dark-green leaves.

English ivy is believed to have been brought to the New World by European settlers in the 1700s. The original importers may have appreciated that the plant is hardy, tolerant of shade, grows in many soil types, stays green year round, and can be used as either ground cover or a climbing vine.

In the 1800s, planting English ivy next to brick and stone buildings became popular. Ivy was seen as a symbol of enduring growth, and several colleges developed a yearly planting tradition known as Ivy Day. Some of the East Coast’s oldest universities became known as “Ivy League” schools for their historic, vine-covered buildings.

While Ivy League colleges are highly desirable, the vines for which the league is named are not! English ivy is now considered an invasive plant in New Jersey, meaning it’s not native to our state’s habitats, and once introduced can quickly reproduce and spread, causing harm to the environment, economy, or human health. Many other states consider English ivy invasive as well.

It’s a bit ironic that the host town of Princeton University – New Jersey’s only Ivy League college – is warning about the negative effects of English ivy on trees. On its website, the municipality of Princeton details the many ways that ivy weakens tree health:

  • It blocks out sunlight, reducing trees’ ability to produce energy through photosynthesis;
  • Adds substantial weight, which can cause mature trees to topple during severe storms;
  • Strangles young trees due to their weight; 
  • Competes for water and nutrients, which can decrease tree vigor;
  • Accelerates rot by harboring moisture adjacent to the trunk;
  • Suppresses nearby vegetative growth;  
  • Holds debris and fungal spores close to the bark which could lead to decline;
  • Acts as a reservoir for bacterial leaf scorch, a pathogen that afflicts maples, oaks and elms;
  • Hides tree defects that could pose a threat to adjacent structures.

Mike Van Clef, director of the New Jersey Invasive Species Strike Team, said that when he started learning about invasive plants nearly 35 years ago, English ivy wasn’t considered invasive.

“It makes flowers and produces fruit/seed in early autumn. Freezing would keep them from ripening, so they didn’t spread well into natural areas,” he explains.

Van Clef theorizes that warmer temperatures from climate change “now gives the vines the extra bit of time to make mature seeds that birds are spreading around.”

The vine appears to be much more vigorous in the southern part of the state, he said, covering acres of the forest floor in many places. In northern New Jersey, isolated plants growing from seed can be found anywhere – and it’s likely to be only a matter of time before their growth begins to wreak havoc.

If you discover English ivy climbing up a tree on your property, you should remove it as quickly as possible to save the life of the tree.

Physical removal is preferable to chemical spraying. According to experts, the best way to remove English ivy is by severing the vines all around the tree, about three feet off the ground, either with loppers or a hand saw. Carefully pry the lower section of the severed vines away from the trunk of the tree, taking care not to damage the bark. Next, working your way around the tree’s base, dig up the ivy’s shallow roots and remove the plants from the soil.

Don’t worry about the severed upper portion of the ivy vines – they can remain on the tree. Over the course of several months to a year, they will die and their withered remains will fall off or blow away.

A few warnings: Be sure to wear gloves when handling English ivy, as chemicals from the plant can irritate your skin (similar to poison ivy). Some people also report breathing difficulties when working around the plant, so wear a mask for protection.

Though English ivy is considered invasive and is on the Strike Team’s “Do Not Plant” list, it’s still widely available at nurseries and garden centers.

This would change if a New Jersey Legislature bill aimed at limiting the spread of invasive plants becomes law. The proposed law would prohibit the sale, distribution, import, export, or propagation of certain invasive plants without specific permission from the state Department of Agriculture.

The bill’s initial list of 30 invasive plants includes English ivy and several other vines, such as Japanese wisteria, Chinese wisteria and Japanese clematis. The list also includes invasive shrubs like Japanese barberry, winged burning bush, European privet, and multiflora rose; and invasive trees including tree-of-heaven, autumn olive, and Callery/Bradford pear.

This past January, as the Legislature’s 2022-23 session was ending, Gov. Phil Murphy vetoed the invasive plants bill, saying that it doesn’t adequately consider the existing authority of the state Department of Environmental Protection (DEP). Supporters in the Legislature promptly reintroduced an identical bill in the 2024-25 session.

Hopefully, all parties can work out their differences for the sake of the environment! Though New Jersey is known as a national environmental leader, it is one of only five states in the entire nation without an invasive species law. All of our immediate neighbors – New York, Pennsylvania and Delaware – have such laws.

Even without a law on the books, New Jersey residents can help by buying native rather than invasive plants, and removing invasives from their lawns, gardens and trees!

To learn more about invasive species, and see the Strike Team’s “Do Not Plant” list, go to www.fohvos.info/invasive-species-strike-team/info-center/.

To read the invasive plants bill as it currently stands, go to www.njleg.state.nj.us/bill-search/2024/S1029. To find out what the town of Princeton has to say about English ivy, go to www.princetonnj.gov/1151/Negative-Effects-of-English-Ivy.

And for more information about preserving New Jersey’s land and natural resources, visit the New Jersey Conservation Foundation website at www.njconservation.org or contact me at info@njconservation.org

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