I have a large evergreen tree which has English ivy growing up it all around. The ivy is just on the trunk and goes about 3/4 the way up. It does not seem to interfere with the tree, but the larger vines are deeply embedded in the bark.
I have read conflicting accounts of whether ivy is harmful to trees. Some writers say it does no harm, but others say it is a threat to the tree and should be removed. Who should I believe?
Well you're right, there are mixed opinions about letting ivy grow up trees - I incline to the view (from experience) that it shouldn't be allowed to do so. Depending on the variety of ivy (so called English ivy covers a lot of varieties), and variety of tree, the likelihood is it will end up in the crown of the tree, blocking sunlight and air to the foliage and branches. Eventually, when you look at the tree, all you'll see is what looks like an ivy tree, with little sign of the tree beneath. The ivy roots into the bark only to climb upwards, it doesn't take nutrients from the tree via that route, though it certainly competes for both water and nutrients with the tree roots. Some gardeners believe Ivy only grows up trees which are already partially 'unwell', so to speak, usually because the tree often falls in later years - the likelihood is the weight and density of the ivy has completely smothered the tree and caused or hastened its demise.
It will by now be well rooted into the bark of the tree, so if you decide to remove it, just cut the woody and green stems at the base of the tree, but don't attempt to pull the growths off if there are a lot, there's a risk they may remove the bark if you do. The growths will shrivel over time and all the leaves will drop off. The stems may remain for some time, but should eventually start to disintegrate.
I am visiting England at the moment and see large deciduous and conifer trees with English Ivy on them that appear quite healthy. Trees and other organisms can live together in combinations of symbiosis or commensalism that are a community where all plants benefit.
This article indicates that where ivy is native it only harms trees that are already in decline. For many other occurrences it provides nectar for butterflies and shelter for animals.
If you are managing the area for the overall health then you should leave the ivy on. If it starts going to the top and covering leaf bearing branches then some pruning is in order.
I would think it is much more cost effective to trim the English ivy from the infected tree when the ivy is still reachable from ground level. I suspect it is best to it the stems manually at the groundling and remove the vines after they have died and the vine roots attached to the bark are disintegrated enough to allow removal without damaging the bark of the host tree. The time interval for sufficient vine disintegration could well be many months or seasons before removal without damaging the bark of the host tree. While waiting the attendant should make sure new growth is not starting to grow up the tree by either physically removing the vines from around the base of the tree or spraying a brush herbicide around the tree. If you wait till it gets up into the branches you would probably have to employ an outside contractor with a bucket lift truck to remove the vines. This could prove to be outrageously expensive and inappropriate. I
