Growing Concerns 556: Tree, english ivy, Prune tree

Late Winter!

Michigan trees stand fast in clutches of English ivy


Dear Janet,

I have a tree about 20 feet tall. An ivy was planted at the base of the tree and it has crept up the trunk and on to some of the branches. It's about 15 feet up. Will this ivy smother the tree and kill it? What should I do?


Dear T.D.,

Vines kill trees by encircling wood and preventing it from growing, by shading out the host plant, or a combination of these two tactics. If the vine on your tree is evergreen English ivy (Hedera helix), it's not able to do the one and prevented by our climate from doing the other, so you don't have to worry.

English ivy doesn't cling by twining so it won't girdle the trunk or limbs and kill them, like bittersweet can. The adhesive rootlets on ivy vines allow them to hold onto the tree but do not damage the bark or wood.

English ivy is also unlikely to shade out a tree, here where winter temperatures dip regularly below freezing. An evergreen ivy needs the protection of the tree limbs, bare though they may be, to survive Michigan winters. So fifteen feet may be as far up as it goes. Only in milder climates can it reach the top of the tree, spread out and thrive there from year to year, eventually killing the tree by depriving it of light.

Deciduous ivies are the ones to watch out for. Species such as wild grape and Virginia creeper can survive the cold to overtop a small tree and gradually kill it. 

One other problem ivy can cause is to make a tree's canopy so dense that it becomes a sail on windy days or holds extra snow or ice. Trees heavily festooned with vines will often topple in an ice storm or when strong winds blow. Once again, this isn't usually a problem with English ivy in Michigan, since it only survives close against the trunk, never bridging the gaps between trunk and limbs to create a sail.

Short reports

Support your local garden center.

Stop in to enjoy the warm sun in your local greenhouse. While you're there, ask what's cooking. You'll probably hear about new, high-demand plants and may even be able to reserve one for yourself. You're also likely to learn that fun, educational events are coming up at the garden center to usher in spring.

It's high time to prune trees.

If you have trees or shrubs that need pruning, call your arborist or sharpen your saw. Make your cuts during the next mild period. It's a great time of year for this work because there are no leaves in the way. You can prune to improve the plant's framework.

It's also a plus to prune before heavy sap flow begins. Although it's not a problem for most trees to lose from pruning wounds, the "weeping" does tend to bother the tender-hearted gardener. In a few species the smell of the sap or exposed wood can attract harmful insects. In the case of oak trees, it's essential to prune before growth begins, so the smell of cut wood is gone before beetles that carry oak wilt fungus begin to fly. Oak wilt, a disease relatively new to our area, is taking a terrible toll on our oaks. It can kill even a very large tree in a single year.

March is not too late to apply anti-desiccant for the first time.

She didn't use Wiltpruf or another anti-desiccant coating last fall, but P.L. says she'll do it now if it can still do some good. Spray away, P.L.!

In an exposed site, wind and sun can damage the foliage of a rhododendron, azalea, Japanese andromeda (Pieris japonica), holly or other broadleaf evergreen anytime between Thanksgiving and Easter. So leaves may already have some wind-burn or freeze drying damage, but there are more bad days coming. What you do now can prevent additional damage.

P.L. also asks how long the coating lasts. That varies, depending on how much sunlight and wind there is, since the coating degrades in the sun and with abrasion. We know it can't last through four months, even if those are gray, calm months. We also know chances to re-apply are limited to days above forty, so we do the best we can by giving delicate plants a second coat half-way through, during a February thaw.

Why bother? The leaves of my rhododendron are still fine!

You may not see the damage to foliage yet. They are like the needles of a cut Christmas tree, able to remain green long after the tree is felled. Often the portions of a leaf that dry out and die in winter don't lose their green and develop that scorched margin until the shrub "wakes up" in spring.


Green thumbs up

to horticultural professionals who take the time to learn or refresh their skills during winter. 


Green thumbs down

to the wise-guy of long ago who reconciled the difference between our calendar and the skies by adding an extra day to February every four years. We can be certain that genius was no gardener or the leap day would have been tacked onto a more deserving month during the growing season!


 Originally published 2/28/04