After over-watering, planting too deep is the second most frequent cause of death for young trees. Trees need water, oxygen and warmth, so they naturally grow most of their roots close to the surface. If these surface roots are covered up, growth stops and roots wither and die.
It’s common for too-deep newly-planted trees to attract insect pests and disease, because these dangers naturally seek out distressed trees as hosts. Even if the tree could adjust to transplanting, growing new surface roots so it can breathe, it falls victim to bark borers or other pathogens.
The part of a tree where the stem and root system meet, called the root collar, is a “flare” between the trunk and the roots. Large roots called buttress or transport roots spread out from the root collar. They steady the tree and “pipe” water and minerals up from the soil. If transport roots are buried too deep, the energy that a newly planted tree needs to overcome normal transplant stress is instead used just to survive.
As much as 90% of a tree’s root system is removed when it is dug up in the nursery. Fortunately, most of the tree’s stored food reserves are in the part that’s left. The key to survival is for the tree to re-grow its root system as quickly as possible. Field-dug balled-and-burlapped (B&B) trees that are planted too deep usually die, because they use up their stored energy trying to survive being smothered.
A tree should be set in the hole with its root flare level even with the surrounding soil. It takes only a few minutes to find the root flare before planting: pull back the burlap and scrape any extra soil off the top of the root ball until you can see the buttress roots on the surface. This can save you some digging, since the root ball may not be as tall as you thought once the excess soil is removed; your hole doesn’t need to be as deep.
Sometimes trees are planted too deep, or have soil hilled up around them, just to keep the tree from blowing over. The right way to do this is by staking, not by piling too much soil on the roots. You should be able to see the root flare and the buttress roots when you’re finished planting.
Avoid piling mulch too deep right around the tree trunk, a common practice often called “volcano mulching”. Not only does excessive mulch smother the roots; heat from its decomposition can literally cook a tree’s trunk. Three inches of wood chips are plenty to control weeds and keep the soil cool. Keep mulch a few inches away from the trunk. We recommend pine bark nuggets, since they allow roots to breathe better than fine-shredded mulches do.
When buying balled-and-burlapped trees, it’s very important to get them from a quality nursery, where the root ball is big enough for the size tree you’re buying. Digging too small a root ball is the easiest shortcut for a nursery to save money, since they can handle and ship more trees per truckload. Good nurseries conform to industry standards, sizing the root ball correctly for the thickness of the tree trunk. For more information on nursery standards and tree quality guidelines, check this link: https://goodseedfarm.com/ArticleTrees—ANLA-Standards-2018.htm
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.