Much maligned, ivy is often accused of strangling trees on which it grows. The reality is often less sinister but there may be times when its control is advisable. In the border, ivy’s dense growth can swamp other plants and control here is often needed.
What is ivy?
Ivy is a woody stemmed, self-clinging climber that can grow quickly into the canopy of a tree. Where it grows as a trailing, ground-cover plant it roots in at many points and its stems extend over a wide area.
The botanical name for ivy referred to on this page is Hedera and it includes the native climber English ivy (Hedera helix). These are unrelated to the deciduous climbers known as Boston ivy (Parthenocissus tricuspidata) and Virginia creeper (P. quinquefolia).
Just how harmful is ivy? Here are some facts that will help you decide;
- Ivy growing on trees is often thought to be a serious problem, endangering the health of even very large trees. However, its presence on the trunk is not damaging and where it grows into the crowns this is usually only because the trees are already in decline or are diseased and slowly dying
- If the branch canopy becomes thin and allows sufficient light to enter, the ivy will develop into its arboreal form. Fraxinus (ash), a naturally thin, open-crowned tree may suffer heavy infestation, and for this reason ivy on ash trees is often controlled
- When trees grown for their stem or bark, such as birch and some acers, keep the stems or trunks free from ivy
- On other trees, ivy can be allowed to grow on the trunk, although one problem with very old or damaged trees is that the ivy may hide cavities which, in time, could gradually enlarge and possibly affect stability
- Ivy is not a parasite; the short, root-like growths which form along climbing stems are for support only. Its own root system below ground supplies it with water and nutrients and is unlikely to be strongly competitive with the trees on which it is growing
- Ivy has much wildlife value. As ground cover in woodland, ivy greatly lessens the effect of frost, enabling birds and woodland creatures to forage in leaf litter during bitter spells. Growing on trees, it provides hiding, roosting, hibernating and nesting places for various animals, birds and insects (including butterflies), particularly during the winter months and in areas where there are few other evergreens
Note: If you are concerned about an old or diseased tree, always seek professional advice from an arboriculturist or tree surgeon.
As ivy is not directly harmful to trees and is beneficial to wildlife, control is not usually necessary. However, where it is undesirable either by obscuring attractive bark or adding weight to an ailing tree, control will be needed.
- Where possible, the stems should be cut back to the ground and the woody stump dug out. If proximity to the tree’s roots prevents removal, regular cutting of the stems to ground level may weaken the ivy over time but is unlikely to kill it
As an unwanted ground cover
- Dig up all stems and woody roots. This may be difficult on heavy soils or where vegetation is very dense. Where the site is not needed for planting, an alternative control method is to clear away all top growth before laying weed-control fabric and a 10-15cm (4-6in) deep layer of bark mulch. Leave in place for at least two growing seasons
- Glyphosate and triclopyr: Ivy that is growing vertically can be killed by severing the stem close to soil level and treating the stump with a stump and rootkiller (e.g. Scotts Roundup Tree Stump & Rootkiller, Bayer Tree Stump Killer, Doff Tree Stump & Tough Weedkiller and William Sinclair Deep Root Ultra Tree Stump & Weedkiller) or triclopyr (Vitax SBK Brushwood Killer)
As an unwanted ground cover
- Glyphosate: Ivy is not easily controlled by means of weedkiller sprays, partly due to the very glossy, moisture-resistant nature of its leaf surface. In this situation it is best to try the tough formulations of glyphosate (e.g. Scotts Roundup Ultra 3000, Scotts Tumbleweed, Bayer Tough Rootkill, Bayer Super Strength Glyphosate or Doff Knockdown Maxi Strength Weedkiller) or for spot treatment use Scotts Roundup Gel. It is essential to avoid spray coming into contact with the foliage or green stems of other plants, so cover adjacent plants with polythene, kept in place until the spray has dried. Bruising the leaves by trampling or with the back of a rake prior to treatment may help with the uptake of the weedkiller
- Triclopyr: In rough grass areas, Vitax SBK Brushwood Killer, containing triclopyr, can be used as it should not seriously damage long grass. However, it could affect the developing growing points of bulbs, particularly if applied in late winter, causing foliage and perhaps flower distortion in the season following application. Therefore, if treating areas under-planted with bulbs, avoid run-off into the soil as much as possible.
This information is taken from the RHS Website and can be found in full here.