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Great Gardening: Wind damage to trees, bushes is a real concern

Wind is annoying, tiring and stress-inducing to people. Wind messes up our streets and yards as debris, garbage cans and litter blow around. But wind is even worse than that for landscape plants: Wind stresses, maims or kills trees and shrubs. Wind alone is bad enough, but when it’s accompanied by ice storms or heavy snow the results can be devastating.

Spring does not immunize us against wind events. April is a volatile month, with balmy summerlike days alternating with wild storms. Let’s predict where our landscapes are most vulnerable and what damage we can prevent.

Trees at risk

You might think that any big trees that were going to blow down have already done so, given the extreme weather events of the decade. Just when I think my own 4½-foot diameter Siberian Elm has shed every last weak limb, it proves me wrong: Another wind storm, another limb hits the deck or garden beneath. Trees age and decay every day. Ideally all tree owners would have an annual arborist checkup. But just in case that won’t happen, the ISA (International Society of Arboriculture) strongly advises you take action when you see these clues:

• Decay: People often ask me about carpenter ants that are “killing their tree,” and I explain that the ants aren’t the cause but a symptom. They are drawn to decaying wood. If a tree branch is dead or decaying, you can prune it off. If the decay is in the tree trunk, that can be dangerous. It takes an expert to determine whether the tree can or should be saved.

You can prevent much tree decay by good horticultural practices: Never wound a tree trunk with a weed whacker or lawn mower (yes, bumping the trunk counts), and do not pile mulch against the tree trunk. Do not plant trees too deeply: You should see the root flare above the ground.

Don’t let stakes or ropes or anything else cut into tree trunks. Don’t leave branch stubs poking out when you prune, and don’t cut flush with the trunk; a proper pruning cut is just outside the swollen area called the branch bark collar. Ensure proper drainage – suitable for the species – when you site a tree.

• Weak structure: If a tree has major trunks that grow tightly together in a tight V, you’re seeing what arborists call a “co-dominant leader.” The bark is “included” – encased between the two trunks – and it is the place where one of the trunks or branches will crack, often leaving a gaping wound. Early in the life of the tree one of those trunks or branches should have been removed. In a healthy structure, two branches have a rough ridge connecting them in a gentle U or curve form.

Prevention includes careful selection of young trees with strong structure and no co-dominant leaders – and correct pruning. However some kinds of trees such as red maples, willows, European mountain ashes, silver maples and littleleaf lindens typically have this kind of structure.

• Girdling roots: Some trees are inclined to have roots that grow in a circle near the soil surface, eventually cutting into the trunk or strangling other roots. Over time the tree becomes weak on one side, without anchoring roots where they are needed, so a wind storm blows it over. Norway, silver and red maples are notorious for this.

Sometimes you can prevent girdling roots by root pruning when you plant trees with a root ball indicating the tendency. If you discover bigger trees with girdling roots, a professional arborist should advise how to cut the offending structures.

• Tree placement: It should go without saying that healthy plants are those planted correctly and in the right site for the species. The right site should include the wind factor: Are you placing, or have you placed, a vulnerable tree where the wind blows strongest? Such trees could include evergreens with shallow root systems, oak trees that hold their leaves all winter, any trees in high-stress situations, or any tree that is just marginally hardy for your USDA hardiness zone.

Poor placement includes planting the giant shade trees of the future too close to buildings. A tree is weakened if its roots can’t reach out because they’re bumping into foundations and driveways. And then it imposes higher risks in wind storms because its branches land on the roof, the car, the garden or the animals and people. When you plant a tree, consider that most of its roots should eventually grow out beyond its outermost branches. Place a small, ornamental tree more like 20 feet from the house rather than 8 feet; wide foundation beds are attractive and better design. Place a giant shade tree – even if it’s small now – far from the house or the street.

Wind and small stuff

If a recently planted shrub or small tree blows over and half of its roots are sticking up in the air, you may be able to save it by righting it quickly and packing the soil back down. Help it by adding some compost into the packing mix. Then stake it (protecting the trunk with something soft) to prevent future blow-overs. A professional arborist anchored my 25-foot Siberian spruce, that was half lifting from the soil, by placing a boulder to anchor the roots on the windy side. It worked.

The other way that wind damages plants is by drying them out. Wind hurts evergreens especially in winter, when the frozen roots can’t take up moisture. In spring you’ll see browning on the windward side of arborvitae, boxwoods and many others. Sometimes they grow out of it, and sometimes you must prune or replace. Fences or hedges as wind breaks, different placement or different plants might have prevented the problem.

Wind is not the landscaper’s friend, nor yours if you have a yard. But foresight, some preventive steps and confidence about what to do may help you cope slightly better with the inevitable winds of spring.

Sally Cunningham is a garden writer, lecturer and consultant.