It’s annoying when a newly planted shrub or perennial dies on you, but unless it was a gift or it’s rare and hard to replace, it isn’t all that serious. Trees are another matter. Young trees can be expensive, and it takes quite a bit of effort to plant one. Most importantly, if the failing tree takes several years to die, there’s precious time lost in achieving the purpose for which you planted it, whether for fruit, shade, a focal point, screening or just a nice, imposing plant companion.

We can’t always know for certain why a tree dies, but many losses are explainable — and avoidable. A perfectly healthy tree can be compromised at planting time by planting too deep, planting in poorly drained soil, failing to pack soil properly around the roots, failing to water it in to settle the soil or failing to stake a tree exposed to the wind. Herbicides, sprayed on weeds but drifting onto tree leaves or even young, green bark, can be fatal. Trunks can be nibbled by rodents, strangled by labels or support wires. It’s amazing so many trees make it.

One easily avoidable cause of tree death is also the most common — at least that’s what an instructor told us in Master Gardening class. She called it mower disease. Someone  mowing around a young tree bumps into the trunk and damages the bark. Young tree bark is surprisingly sensitive, especially in spring. Even a string trimmer can make a wound. The mower or trimmer operator may scarcely notice a bump that’s hard enough to bruise the bark and damage the underlying cambium, the tree’s growing layer.

This mechanical damage alone is not usually enough to kill a tree outright, unless it happens repeatedly, killing cambium around the trunk’s entire circumference, thus “girdling” the tree. But even a small wound can provide an entry point for disease vectors, leading to rot that may eventually prove fatal. Mower disease is easily avoided by maintaining a grass-free, weed-free, mulched zone around the trunk, at least three feet in diameter. Make the circle larger as the tree grows, and hand-weed next to the trunk.

Another common cause of tree failure can take many years to become evident because it happens largely below ground. The problem is root girdling. It occurs when one or more roots arising near the trunk take a direction that will eventually cause it to strangle some or all of the remaining roots. Girdling roots can develop when a tree is planted in a confined space, or in a hole dug in compacted clay soil and backfilled with something better than the roots prefer to grow in. When root girdling develops after planting, it will usually cause problems for just part of the tree, or one whole side. A search at or just below soil level may reveal a point of strangulation. In that case, the offending root can often be cut out.

A more insidious kind of root girdling begins in the nursery, before you purchase the tree. When a tree — or shrub, for that matter — is raised in a container, root growth is restricted by the size of the pot. Imagine a very young tree is left in a small pot for too long, so that one or all of its main roots grow round and round inside the pot and form a spiral. When that young tree is transferred to a larger container, the roots may continue to grow in the pattern they established in the little pot, but their diameter will steadily increase — a recipe for self-strangulation.

You can avoid this problem by buying bare-root plants, if you can find them. Bare-root fruit trees are still readily available. Another way is to buy trees balled and burlapped. If you buy a small tree in a pot (a common way to buy ornamental trees these days)  poke around at or just below the soil line, to see if the roots radiate out in a natural way from the trunk. If the tree is dormant, wash off some or all of the soil to inspect the roots, and correct any problem that comes to light. If the roots appear normal near their origin, it is still a good idea to look at the roots on the outside of the root ball. Does the tree appear pot-bound, with roots circling the root ball inside the pot? If so, make at least one vertical cut from top to bottom to sever any circling roots. I prefer to make three cuts, then “rough up” the root ball surface a little.