English ivy

(Hedera helix)

 

 

Invasive implications

English ivy is a widely planted evergreen vine, introduced as an ornamental into North America from Eurasia during colonial times. As a garden escapee, this vine quickly spreads into neighboring forests and is especially invasive in coastal regions from Oregon to British Columbia. It has two distinctive growth stages. "Juvenile" plants grow along the ground and "arborescent" or treelike forms are erect shrubs. It is this second form that causes significant environmental damage. As an arborescent, English ivy can completely cover walls, buildings, roofs, and trees; this added weight often causes trees to topple when exposed to strong winds. On the ground, English ivy, because of its dense growth and abundant leaves, prevents light from reaching important native plants. This amazing vine can reach heights of 50 meters and depths of 1 meter above ground. Despite its invasiveness, English ivy is a much sought after ornamental plant, treasured for its attractive shapes, colours and habits. In fact, there are many advocates of this vine that are quick to point out its benefits. These include providing shelter for bats, birds, and invertebrates along with nectar for insects. Some even claim that ivy only pulls down trees if they are already dying. However, it is indisputable that ivy inhibits the growth and regeneration of native wildflowers, shrubs and trees through shading, smothering, and through associated harmful pathogens (bacterial leaf scorch Xylella fastidiosa). This invasive plant is widespread in southwestern B.C. and should be recognized and removed on sight. Controlling English ivy requires persistent efforts to make significant headway.

 

Identification

Spring

Summer

Winter

  •  young leaves are bright green and glossy

 
  •  ivy grows throughout most of the year but thrives in warmer summer temperatures
  •  this evergreen keeps its leaves all year round

 

Leaves

Stem/Roots

Flower/Fruit

  •  note: top picture is groundcover leaf while bottom is the rounder arborescent leaf
  •  emerge light green and change to dark glossy green, waxy
  •  juvenile form 3-5 lobed, heart shaped base
  •  green-white venation radiating from upper part of leaf
  •  length: 3.5-8.5cm width: 2.5-8cm
  •  vines attach to bark of trees, brickwork, etc. via small rootlike structures or suckers that secrete a glue-like substance (arborescent)
  •  horizontally spreading shoots near base of plant (juvenile phase)
  •  young stems are 3 to 6 mm in diameter
  •  umbrella-like clusters of small, green-white flowers in fall (20-25), sparse and rarely seen - mature growth only (4.5cm x 3cm)
  •  black fruits mature in spring, fleshy outer covering encasing one or more hard seeds

 

Key Features

English ivy belongs to the Ginseng family and is reportedly poisonous if consumed. Growing in full sun to full shade, it thrives in an array of areas although preferring moist, well-drained soils in partial sun. English ivy has adapted to many adverse conditions including heat, drought, a wide pH range, and compacted soils.

As mentioned, it exists in both juvenile and arborescent forms. The first grows like a thick mat, choking out other plants or even small streams. Crawling along the ground, the juvenile vine extends until reaching a vertical face to ascend. As this point, English ivy turns and grows upwards along the face, using hairy rootlets to tightly adhere to rough surfaces. Once it can no longer climb, it stops and sends out tendrils without rootlets. Soon after, the juvenile form transforms into an arborescent form, producing new rounded and smooth edged leaves (as opposed to the pointed and lobed leaf). Now it grows as a dense, heavy and stoutly branched shrub, posing a threat to trees and shrubs.

This mature form can produce flowers in the fall and fruits containing hard seeds in the spring. Seeds are mainly dispersed by birds such as starlings, robins, and sparrows. It also reproduces vegetatively via cuttings or from stems contacting the ground (juvenile).

 

 

Control Measures

As English ivy is a serious threat to tree blow-over during storms, it is important to take measures to kill both arborescent forms as well as groundcover vines. Currently, there are several techniques to control English ivy including non chemical and chemical methods. Removing the tree form of English ivy is certainly more difficult than removing it as a groundcover as vines can grow up to 50 meters high! However, starving the vine results in withering and die off in time. To date, there are no biological controls agents used to control this invasive plant. 

 

Non Chemical Control
  Hand pulling Cutting
How Vines can be pulled out by hand with some difficulty.  Cut climbing vines at reachable height to kill upper portions. Use a large screw driver or forked garden tool to pry and snap the vines away from tree trunks. It may be necessary to use an axe or pruning saw for larger vines.
When In late summer or fall; easier to remove when ground is moist; before seed sets In late summer or fall
Duration

 

 Efforts must be long-term until stands are eradicated - may take several years depending on size of area and intensity of efforts. Rooted portions of vines will remain alive - should be pulled and repeatedly cut.
Pros/Cons Safe and effective method but labour intensive Good results and cost effective but labour intensive, requiring persistent efforts

 

Chemical Control
  Basal bark Applications Foliar Application
How Apply a 15-30% solution of triclopyr ester (Garlon 4) to stems of vines that are growing up into tree canopy Apply a 2.5% mixture of triclopyr amine in water to the leaves or cut first, allow to re-grow, and apply the same mix to new foliage. Herbicide will be absorbed through the stem bark for greater effectiveness.
When

Any time of year as long as temperature is above 12o C for 1 or 2 days. However, best to apply in fall/winter when native species have died back or are dormant

 Any time of year as long as temperature is above 12o C for 1 or 2 days. However, best to apply in fall/winter when native species have died back or are dormant
Duration

 

 Repeat herbicidal treatments are likely necessary; follow-up monitoring should be conducted to evaluate the success of treatments. Repeat herbicidal treatments are likely necessary, follow-up monitoring should be conducted to evaluate the success of treatments.
Pros/Cons Very effective but costly and possibility of host tree absorbing herbicide Effective and less laborious than hand pulling. See chemical warning below.

 

Control Warnings:

Disposal - Make sure to properly discard all plant pieces in thick plastic bags and transport them to a sanitary landfill site or incinerator. Composting is not an appropriate means of disposal as this may result in further distribution. Remember that humans can actually spread invasive plants by taking seeds from one place to another on clothing, tires, equipment, etc.

Chemicals - Although some chemicals are approved for control of invasive plants, extreme caution must be taken as many pesticides are harmful to humans. Permits may be required for chemical use and buffer zones exist beside waterways to protect fish and wildlife. Chemical control is not a long-term solution and therefore should be part of a finite plan and applied sparingly. Please see the following web sites for further information: Provincial: MWLAP Pest Information  Federal: Pest Management Regulatory Agency

Biological - Extreme caution must be taken when introducing one organism to control another. Intensive testing must occur before initiating a safe and effective biological control agent. Please contact local government or environmental agencies to determine available volunteer opportunities.

 

Additional Resources