Newly Planted Sugar Maple

(Question)

Two weeks ago we had professionally planted a 15ft. high sugar maple from container at our cottage in Terra Cotta, Caledon. We have heavy clay soil there and have been going up to water the tree every 3-4 days. We are watering the tree with a fine misting spray for about 2 hours. We are also leaving a large watering bag at the tree trunk. One side of the tree is showing signs of leaf scorch and it is getting progressively worse. The tree is planted about 5m from a mature black walnut tree. The hole dug for the tree was only the size of the plastic container that the tree came in. We had them place about 4 in of crushed stone on the bottom of the hole. The tree is located in a full sun condition with some shade from adjacent trees. We also applied the Transplanter sold to us at the nursery. This is a replacement tree that was planted in the same location 2 years ago. The first sugar maple showed also signs of leaf scorch, leaves were turning brown and falling off already in summer on the first year. In the second year the top 3 ft of the tree never developed leafs. When this tree was pulled out, we noticed very little root development beyond the wire cage it came in. What are we doing wrong? Are we overwatering the tree? Please help!

(Answer)

Thank you for writing to the Toronto Master Gardeners. We are sorry to hear that your previous sugar maple had to be replaced and that the new one is also showing signs of decline. Here is what we think why your tree is distressed.

Let us start with the fundamentals: soil. The texture of a soil (i.e. the proportion of sand, silt and clay) cannot be easily changed so it is important to choose a tree that is well adapted to the type of soil you have. Sugar Maple is not an ideal choice because it prefers a well drained acidic soil and not a heavy clay soil. The heavy texture of clay soil is not only difficult for the tree roots to penetrate, it also drains poorly. Roots need air in the soil to breathe, and excess water in the soil can drown the roots. Ironically, the symptoms of a plant with drowning roots is the same as a plant suffering from lack of water—wilting and leaf scorch. A plant with drowning (i.e. non-functional or dead) roots is suffering from physiological drought because it cannot receive water from its roots.

Unfortunately, contrary to popular wisdom, placing coarse materials like gravel at the bottom of a planting hole does not improve drainage. Water moves most efficiently through materials of uniform density. When there is a change in density, waterflow slows down and accumulate at the border where the two different materials meet. Thus a layer of crushed stone under the planting hole actually impedes drainage and causes pooling at the base of the roots.

Therefore, one probable cause of your Sugar Maple’s distress is excess water in the soil. You noticed that the planting hole was only the same size as the container in which the tree came. After planting, it is effectively sitting in a semi-impenetrable hole, surrounded by heavy clay and crushed stones, both very different in texture to the growing medium in its original container. Its roots will have difficulty pushing out into the clay, while excess water cannot drain away freely. In time, the roots will gradually weaken, rot and die, resulting in the tree being dehydrated and malnourished. The first sugar maple may have failed for the same reason. As a tree struggles and become weak, it becomes vulnerable to winter kill, diseases and pests, any one of which could have been the cause of your previous sugar maple not leafing out in the top 3 feet.

When you next visit your Sugar Maple, check the soil around it to see if it is wet. If so, then refrain from watering until all excess water have drained away. Adjust your watering schedule so that the roots get a deep watering less frequently, to account for the slower drainage.

Please also take a look at a previous Toronto Master Gardener answer on other possible causes of leaf scorch on Sugar Maple. We do not think that the Black Walnut is culpable since Sugar Maple is considered Juglone tolerant.

Planting a tree is a major investment and it is worthwhile to seek the professional advice of a certified arborist; find one in your area by starting your search here. We wish you the best of luck in getting your Sugar Maple back to health.