Arborvitae need winter watering

Q. I have brown spots all over my arborvitae. What is wrong?

Steve from Poland (and others!)

A. While arborvitae make a great living fence and provide evergreen color year-round, they are commonly plagued with disorders, diseases and insects. Finding brown spots in late fall is a worrisome issue, though, as it does not speak directly to winter injury like we commonly find in spring.

Many arborvitae problems relate to how these medium-sized trees were planted, the location in which they were planted and moisture levels throughout the year. We have several arborvitae in our back yard that have been the same size for years. This is because they were planted in heavy clay soils that stay consistently wet through winter and early spring. They are short, but beautifully green.

In our clinic and through this page, we continually speak to the need for consistent moisture throughout the year for evergreens, as they transpire (lose water) year-round. The biggest challenges are during winter when evergreens are more likely to lose more water than can be absorbed through its own root system. It’s not just the cold, it is the drying, desiccating winds that do the most damage in the winter.

Thus, year-round care is important for all evergreens in our area. We need to provide ample moisture from late summer into winter as long as the ground is not frozen. A soaker hose, irrigation system or other method of watering works just fine.

But what exactly is wrong with a specific arborvitae? We really need a sample to be able to tell. If we can’t find an insect issue or identify a fungal pathogen, the problem is most likely stress. Stress can come from compacted soil around the roots, reducing the air needed by roots. It can come from not getting water during this year’s very dry September.

Arborvitae issues are never easy, because stress shows up late in these plants. It is difficult to tell because evergreens have a waxy coating. This coating protects the needles from drying out, but also prolongs browning due to stress and other issues.

To help you get a start to figuring out what is wrong with your arborvitae, there is a key to identifying issues and diseases of arborvitae at: http://www.extension.umn.edu/garden/diagnose/plant/evergreen/arborvitae/patchyyellowtobrowndiscoloration.html

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Winter hours for the Plant and Pest Diagnostic Clinic vary. Submit questions to the clinic at 330-533-5538 or drop samples off to the OSU Extension Office in Canfield.