Ginseng Family – Araliaceae

Native Range: Europe, western Asia, northern Africa
Invasive Range: North America
Woody, evergreen, perennial vine, trailing or climbing

A Charlottesville Area Tree Steward removing English ivy

Overview

English ivy is an evergreen perennial climbing vine, with triangularly heart-shaped, glossy-textured leaves. It was introduced by European colonists as early as 1727.  It has been one of the most popular, widely planted ground covers throughout North America, planted for its evergreen foliage and dependability as a “carefree” groundcover.

It is a vigorous grower and once established, forms a thick, sprawling groundcover, and if a tree, fence, wall, or building structure is handy, ivy’s aerial roots grab on and soon climb over it.  These aerial rootlets exude a gluelike substance to help them cling to upright structures. Vines can grow 90 feet up tree trunks, spread out, and cover the branches and twigs, blocking sunlight from reaching the host tree’s leaves thus impeding photosynthesis.  The tree will exhibit decline over several years and eventually die.  Moreover, the added weight to the vines also makes the tree more susceptible to blowing over during storms.  As a groundcover, the thick leaves completely outcompete or reduce light to plants underneath thus suppresses native plants in the understory. Thick ivy growth can accelerate rot by holding in moisture, which can also attract mosquitoes.

Although it is recognized as a serious weed of natural ecosystems, parks, roadsides, and urban landscapes, it continues to be sold and marketed as an ornamental plant in the United States.  Vast resources, time, and labor has been spent attempting to manage infestations in our public and private landscapes. Old tree-lined streets and parks add value to property and quality to our lives. English ivy is a threat to that investment. Protect your trees, landscaping investments, and home from English ivy by removing it and not planting it either.

Ivy is still being sold in nurseries across Virginia. Image: Tim Maywalt

Habitat

English ivy is found throughout, but especially in the eastern United States and in the West, from Arizona to Washington State. It is able to tolerate shade and this helps it flourish in the forest understory. It grows well in full sun conditions, adaptable to a range of moisture and soil conditions including rocky areas.  It tends to like moisture but not extremely wet conditions, dislikes drought and salinity. 

English ivy tolerates a wide range of soil pH but prefers slightly acid (pH=6.5).

Habitats invaded include the forest edges and openings, fields, slopes, disturbed areas, urban areas, and landscapes. 

Description

This perennial evergreen woody vine has a slender appearance when a ground cover but the stem can grow up to 1 foot in diameter when climbing trees and rocks with the many fine aerial rootlets.  It becomes a woody stem, covered with gray-brown shiny bark, bumpy and gnarly with the aerial rootlets, and generates upright branches capable of climbing to 90 feet.

Flowers & Fruits

Vines may grow for up to 10 years before producing flowers. English ivy flowers from June to October, typically under full sun conditions, only on mature upright branches, typically up a tree.  The flowers are small greenish-yellow and occur as terminal hairy-stemmed single umbel clusters at tips of stems. They have globular starburst type inflorescence at tips of flowering stems, as single umbels.

Fruits are “drupes”, black with a fleshy outer layer and stone-like seeds. The drupes are 7-8 mm. appearing pale green in late summer ripening to dark blue to black in late winter to spring. 

Leaves

Juvenile leaf (left) and mature leaf (right). Image: Tim Maywalt

Leaves are alternate, dark green with white veins, less than 3.3 inches wide, waxy, and somewhat leathery. It has extremely variable leaf forms, from unlobed to 3-5 lobed. The most common form for the juvenile (pre-flowering) plant is three palmate lobes. After maturing the most common form is a single lobe leaf. In sun the leaves may be oval in shape with no lobes.

Note: there are many cultivars including ones with smaller leaves and white or gold, variegated markings.

Ivy plants can have both juvenile and mature stems:
– Leaves on non-flowering stems (juvenile stage): dull green, lobed, with distinct light veins; stems produce roots at nodes; most common leaf type on the plant.
– Leaves on flowering stems (mature stage): glossy green, unlobed; stems produce umbrella-like clusters of greenish flowers, followed by dark berry-like fruits.

Stems

Ivy rooting at nodes (image: Michigan State University)

The stems can reach up to 1 ft in diameter. The aerial rootlets exude a gluelike substance to help them cling to trees and other structures. New research indicates that the glue is not the only factor involved. The root actually changes shape to anchor the plant. It also produces root hairs that fit into crevices in the support. It has thick filaments which allow it to adhere to trees and structures.

Lifespan

Plants are long-lived, 50 to 100 years or more.

Ecological Impacts

English ivy is a vigorous growing vine that impacts all levels of disturbed and undisturbed forested areas, growing both as a ground cover and a climbing vine. As the ivy climbs in search of increased light, it engulfs and kills branches by blocking light from reaching the host tree’s leaves. Branch dieback proceeds from the lower to upper branches, often leaving the tree with just a small green “broccoli head”. The host tree eventually succumbs entirely. In addition, the added weight of the vines makes infested trees much more susceptible to blow-over during high rain and wind events and heavy snowfalls. Trees heavily draped with ivy can be hazardous if near roads, walkways,
homes and other peopled areas.

On the ground, English ivy forms dense and extensive monocultures that exclude native plants.

English ivy provides hiding places for rats and other vermin. Shallow-rooted ivy mats on hillsides can increase risk of slope slippage.

English ivy serves as a reservoir for bacterial leaf scorch (Xylella fastidiosa), that infects a variety of trees including oaks (Quercus spp.) elms (Ulmus spp.), and maples (Acer spp.).

Other Concerns

The entire plant contains glycoside which could cause toxicosis if ingested. Symptoms include gastrointestinal upset, diarrhea, hyperactivity, breathing difficulty, coma, fever, polydipsia, dilated pupils, muscular weakness, and lack of coordination. The sap can cause rashes in some people. If birds eat the drupes, the glycosides can be mildly toxic.

How it Spreads

English ivy spreads by bird-dispersed seeds and vegetatively by vines or stem fragments that can root at the nodes. New plants grow easily from cuttings or stem fragments that make contact with the soil.

Management Strategies

Biological

There are no biological controls for English ivy although goats will eat the leaves.

Goats are effective at removing leaves, but since they leave the root system undisturbed, grow-back will occur creating the need for repeated grazing or additional treatment approaches.

Mechanical

Ivy in Trees: You can use garden clippers to cut ivy at the bottom around the entire trunk of infested trees. Two cuts are needed leaving a space of at least an inch or two between the two cuts or the vines can re-seal. Don’t pull the remaining ivy off the tree as doing this can injure the tree. Pull the ivy vines out of the ground around the base of the tree, making a 2 feet “life-saver ring” around the three. Maintain this ring to protect the tree from future infestations. Further information

Ivy on the Ground: Vines growing on the ground can be hand-pulled. This is most effective when the vines are small, the soil is moist, and the area of infestation is small. Uproot vines with a mattock or grub hoe. Wear long gloves to protect your skin.

For larger areas you can use a weed wacker (multiple times) to cut the vines back as close to the ground repeatedly until the roots starve. 

Disposal: Large cut Ivy vines do not reroot if you just leave them lying on the forest floor, but the small stems will reroot and have to be disposed of in such a way that they don’t touch the ground. Either put them in plastic trash bags and dispose of them in a landfill or pile the cut material and allow it to dry out onsite. Cover the pile with heavy branches to keep the wind from spreading the vines. Dried piles of pulled material should be monitored periodically for new growth or hauled away

Smothering / Mulching

Smothering may be an effective choice for smaller infestations when herbicides are not appropriate. First, cover the ivy with an impervious material like cardboard, UV-proof vinyl sheeting, tarps, or whatever. The UV-proof material keeps the vinyl from decaying making it hard to remove once it has done its job. Then, cover the entire infestation with several inches of mulch. This may include wood chips, grass clippings, hay, or similar degradable plant material. Shredded or chipped wood may be the best option since hay and grass may potentially carry weed seeds. Covering the area with cardboard may improve the effectiveness and longevity of this method. The mulch should stay in place for at least two growing seasons and may need to be augmented several times. Mulching can also be done following herbicide treatment.

Herbicides

If applying herbicides to treat English ivy, always read the entire pesticide label carefully, follow all mixing and application instructions, and wear all recommended personal protective gear and clothing. The label is the law. Always ensure you apply the minimum amount of herbicide needed and only to the target plant. Take care to protect native plants.

Foliar Application – As the leaves are evergreen they may be sprayed at any time of the year (June- February is best) with a herbicide provided the weather is above freezing. If spraying an extensive area, add a plant dye to keep track of where you have sprayed. Note the herbicide concentration should be 4 to 6% rather than the normal 2%, because the waxy/leathery surface of the leaves resists herbicide penetration

Cut Stump – A more concentrated herbicide is needed. Cut the vine and use a spray bottle, drip bottle, or dauber to apply herbicide directly to the stump where it comes out of the ground (June-February, but late summer – fall is ideal). It must be applied immediately after the cut is made as the end will quickly seal itself to hinder the penetration of the herbicide.

Hack and Squirt – For very large vines you can treat them as you would any woody plant of that size. Hack multiple cuts (about 2 inches) into the vine leaving space between the cuts (leave at least 1-2 inches between cuts and do not girdle the vine). Then using a sponge dauber, squirt bottle, or paintbrush, apply the herbicide to the cut areas. Larger vines should be left on the tree after cutting and treating. Attempting to pull them off will often strip the bark, damaging the tree. The vines will eventually die, dry out and fall off the tree. Don’t be disappointed with the immediate results of cutting the vines or spraying the leaves – it can take a couple of months before there is any sign that the ivy has died.

Cut Now, Spray Later – In this technique, which is appropriate where there are extensive beds of ivy on the ground, the ivy is mowed with a lawnmower or bush hog. After a few months, any grow-back is sprayed with 4-6% herbicide such as glyphosate (June-February). The site should be revisited periodically and grow-back sprayed until there is no further sign of grow-back or sprouting from the seedbed.

Native Alternatives

Rhus aromatica ‘Gro-Low’ (Fragrant Sumac)
Chrysogonum virginianum (Green and Gold)
Pachera aurea (Golden Ragwort)
Polystichum acrostichoides (Christmas Fern)
Dryopteris marginalis (Marginal Wood Fern)
Parthenocissus quinquefolia (Virginia Creeper)
Onoclea sensibilis L. (Sensitive Fern)
Phlox subulata L. (Moss Phlox)
Asarum canadense L. (Wild ginger)
Geranium maculatum L. (Wild geranium)
Tiarella cordifolia L. (Foamflower)
Native sedges