Trees & Shrubs: Transplant Troubleshooting

By: Dave Zeldon and Ely Schweyer

Let’s get in depth about planting trees too deeply!

Sometimes homeowners find that their newly planted trees start showing signs of stress and become unthrifty a little while after planting, and soon their investment is altogether lost when the plant just dies. Often when we’re asked to inspect a tree in poor health, we know what to suspect.

   Although not readily apparent at the time of installation, the long-term effects of improperly placing the root system in the planting hole are substantial. The poor tree health that results manifests itself as reduced growth rate, atypical leaf size and colour, and increased disease susceptibility. Trees in really poor condition exhibit decay, cracks, and excessive deadwood. Sometimes trees show signs of stress within the first year of planting, but it usually takes several years for the problem to rear its ugly head.

   The most common reason? Many trees are simply buried too deeply causing the tree roots to decline in health, as they cannot get the vital oxygen from the air that they require to live.

Putting Down Roots

The width of the hole your tree will call home should be at least two times the diameter of the root ball, container, or in the case of bare root trees, the spread of the roots. This will provide the tree with enough worked earth for its root structure to establish itself.

   For tree roots to grow vigorously, they require water, oxygen, and warmth. An oxygen level of 25% of the soil volume is considered good for root development.

   At a 5% oxygen level, growth stops, and at 2%, roots decline and die.

   Since tree roots naturally grow quite shallowly in the soil profile, buried root systems are unable to obtain adequate soil oxygen and water. As a survival response, trees work to get roots closer to the soil surface where there is a more reliable source of both. The energy that a newly transplanted tree should use to overcome normal transplant stress is instead used just to survive.

   The tree expends its energy either by forcing its roots to grow upward or by creating totally new roots from dormant buds on the buried trunk, wasting all its prior growth. Some plants can survive being buried too deeply and live normal lives after developing a functional root system, others begin a long, slow decline of health resulting in either premature death or sudden failure during wind or ice storms. Let’s not risk it!

How Do I Know How Deep to Plant?

If you want your new tree to not only survive, but thrive, it needs the best start possible; it is very important that the root collar flare be visible after planting. The root collar is the part of a plant where the stem and root system meet, "flaring" where it transitions between the stem wood and the roots. Always make sure that the root collar flare is visible after planting. If settling occurs, reset the tree to the proper depth.

👉 Note: The backfilling soil should be a mixture of the original soil with composted manure or topsoil and bone meal.

But I Did Leave the Root Collar Visible… When I First Planted It

It has been observed that many times after a perfect tree planting, the homeowner then decides to build a raised-bed garden around the tree (thus burying the root collar flare – we’ve found root collar flares buried to 24 inches in mulch!) only to find that within a year or two, their young tree is dead or dying.

   A common practice, often referred to as ‘volcano mulching,’ also contributes to this problem. In addition to subjecting trees to the problems associated with planting too deeply, heat from the composting mulch can literally cook a tree's trunk.

So, What is ‘Planting Proud’ Then?

   The transplanting rules are amended if planting in the heavier clay soils where the practice of planting your new trees "proud" is advised. Planting proud essentially means that the root ball is left higher out of the ground level, producing a hilled effect. The soil that is normally used for back-filling is used to help to create a mound. Planting your trees this way in poorly draining clay soils prevents the ground water from collecting in an otherwise deep hole and drowning the roots of your new planting.

   But, as a general rule, trees should be transplanted no deeper than the soil in which they were originally grown, and the soil level shouldn’t rise after planting. Two to three inches of wood chips is the optimum depth to mulch - and keep it an inch or two away from the trunk. If it is really desired to have the tree as a focal point in this newly built garden, then possibly a 3 foot well could be made around the tree to keep the root collar flare open to the air.

   So, remember to give your tree a strong start and long life by not planting too deeply, but by leaving that root collar flare exposed! We hope these tips can help you encourage the longevity of your new tree. For more information - and trees - visit our Trees & Shrubs section at Eising Greenhouse and Garden Centre. We hope to see you soon!