What happened to my dogwood tree?

Published 10:23 pm Friday, April 17, 2020

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Their graceful-lying branches with creamy white flowers mark the beginning of spring so beautifully. I have had multiple calls so far this season regarding dogwoods. Many of which consist of the question, “What happened to my dogwood?” As usual, there is no real short answer to this question. By the way, those creamy white flowers aren’t actually the flowers, they are modified leaves called bracts. Just in case you happen to find yourself on Jeopardy, I thought you should know.

Dogwoods are a wonderful tree in their native environment. They complement the understory of a forest well and do not suffer from many of the stresses we subject them to in a home landscape. Growing in a lawn is not their native environment — much like us right now, it is a harsh reality in which they must try and adapt to survive. Dogwoods do not adapt well, however, to these types of stresses. Does this mean that we shouldn’t grow them? Absolutely not! We always need to think, “Right plant; right place!”

A dogwood is well-adapted to growing in a slightly acidic, moist, but well-drained soil. As an understory forest tree, it enjoys protection from heat, cold and the harsh winds that the larger, overstory trees provide. When we take a plant like this and throw it out in the full sun, subject it to the wind, heat and cold, it causes the tree to be stressed. A dogwood tree is not a long-lived tree to begin with, averaging around 80 years in ideal conditions.

There are only a handful of disease and insect pests that plague dogwoods. The worst of which is dogwood anthracnose (Discula destructiva). The good news here is this disease doesn’t usually happen in the coastal plains of North Carolina. Root rots, on the other hand, often kill dogwoods in the coastal plains. These are phytophthora and armillaria root rots that can typically be traced back to soils staying saturated or inundated for long periods of time.

The only insect that will do considerable damage to dogwoods is the dogwood borer (Synanthedon scitula). These holes can often be found near the base of the tree. The borer is the larva of a clear winged moth that resembles a small wasp. The borers will cause decline in older trees and death in younger trees. Look for frass (sawdust) at the base of the trees to see if you may have borers. More often than not, however, it is cultural issues, things that we can prevent, that I find are causes of death in dogwoods.

There are many cultural problems that a tree will be subjected to growing in a lawn which further compound these stresses. First and foremost is improper planting. This is true for most any tree that I am called out to take a look at. We homeowners, and often many landscapers, do not plant trees correctly.

When planting a tree, the first thing to do is prepare the site. This includes getting a soil sample and taking a long look at the drainage of the site. Next, look for the first root on the tree, this should be planted no more than 1 inch below the soil surface. Dig a hole that is twice as deep and two and half times as wide as the root ball on your new tree. Backfill with the excavated soil until the tree will sit at the proper height (again, the first root should be no deeper than 1-inch below the soil surface). Now, plant your tree, lightly packing the soil around the roots. The soil should be lightly mounded to ensure that water will not pool over the top of the roots during a rain event.

The soil will settle over time as rain and irrigation settle the soil. If you are planting a containerized tree (a tree that comes in a container), it is important to check for and prune any circling roots. Nursery-grown trees can be in pots for a long period of time. This can cause the roots of the tree to hit the side of the container and then to grow in a circle. If these roots aren’t pruned off before planting, they will continue to grow in this circular pattern until they eventually girdle the tree. This cuts off the supply of water and nutrients coming from the roots and kills the tree.

Mulch is always a good thing, especially with dogwoods. A good ring of mulch around the tree —  two to five feet in diameter and two to three inches deep — will serve many functions for the tree. It is like a blanket for the roots in the winter and an air conditioner in the summer. Mulch serves to moderate soil temperature, effectively minimizing the highs and lows of the seasons. It will conserve moisture in the soil by lessening evaporation. A good layer of mulch will keep annual weed-pressure down and lessen competition for nutrients with turf. Lastly, mulch protects the tree from mechanical injury by keeping weed trimmers and mowers away from the trunk of the trees. However, like most things in horticulture or life, it must be done correctly. Piling mulch upon the base of your tree, referred to as volcano mulch, has the opposite effect, often causing more stress than not having mulch at all. This will slowly suffocate the tree! When putting out mulch, be sure to keep it a good two to three inches away from the trunk of the tree.

Plant your dogwood in a moist well-drained soil, having full shade to partial morning sun. Make sure to prune dead and crossing limbs out every year. Complete a good pruning of the tree to allow air movement through the tree. This helps dry the tree out after rain and heavy dew to lessen the instance of disease. Having a very shallow root system leaves dogwoods highly susceptible to drought. If we go more than two weeks without measurable rain, make sure to irrigate your tree. If using a sprinkler, do not let the water continuously hit the trunk of the tree, this will have the same effect as volcano mulch. Follow these few simple things and watch your tree flourish!

If you have a question or concern involving horticulture, email gene_fox@ncsu.edu or call me 252-946-0111. While our office is closed to the public, I am working and ready to help you. If you have a question, please send it in — you might even make the paper!

Gene Fox is the area consumer horticulture agent for North Carolina Cooperative Extension.