Dying arborvitae

Asked November 5, 2017, 6:41 PM EST

Dang, one died, now another one is! ( it keeps getting bad these past two weeks) Can I try to put some systemic liquid in the ground to see if it works or is it too late!? They were awesome beginning this summer. I can't see any bugs. They are fifteen feet tall at least and pushing thirty years old. I don't want the others to die.

Washington County Oregon

3 Responses

I'm sorry you lost one of your arborvitae and are having problems with another tree. It's impossible, of course, to diagnose the problem based on a picture. You might want to get the help of a licensed professional arborist. The International Society of Arboriculture http://www.isa-arbor.com/ has a list of them in your area.

I can give you 2 areas of your trees to look at: the leaves and the roots. First the leaves; conifers do lose their leaves (needles or scalelike for conifers), just not all at once like deciduous trees do. They keep their leaves for a few years, then shed them progressively from the interior of the tree out toward the tips where the newest growth is. If the tips are green and healthy looking, your tree may be okay. Secondly the roots; Arborvitae like moist, but well-draining soil. It's especially important in our climate's wet winters and springs. Arborvitae can develop root rot in wet conditions. Plants need air as well as water. Too much water around the roots can damage the roots - they drown from no air. Well drained soil drains water through it, moistening the soil, but leaving open pores that fill with air. With damaged roots the plant cannot take in enough moisture and the tree's leaves don't get the water needed to function, and the tree may die. Fungi like wet conditions with no air and can infect the roots. If you expose the roots on your arborvitae they should be light-colored and healthy looking. If the roots are dark and friable they are damaged and won't function normally. You may also have a discolored area at the base of the trunk of the tree from Phytophthora fungus. Scrape away an area of bark, the area underneath should be light colored and firm, not dark and soft looking. Phytophthora is a common fungal cause of root rot in arborvitae. Their spores swim to infect other areas. Unfortunately, there are not many good treatment options for this infection.

We had a very wet cold winter last year. It was hard on many plants. Then we had a very hot dry summer. If the plant had root damage from the winter, it struggled to get enough moisture, and some were lost.

To help your trees try to create well-drained soil around them. With trees that are 30 years old that can be a challenge. Adding organic material as mulch around the trees, but not next to the trunk will help add organic matter to the soil which helps with drainage. A mulch of 2-3 inches will also help conserve moisture and moderate soil temperature, which can really help in hot dry conditions. A good soaking weekly with a hose at 1/3 power will provide water without washing away the mulch or exposing the roots. This article has additional information on caring for Arborvitae, Tree Care Tips for Arborvitae http://arbordayblog.org/treecare/tree-care-tips-for-the-tree-of-life-arborvitae-thuja-occidentalis/.

Thanks for the quick response. I did have a expert trim my other half of the yard arborvitae. In June, all were watered well and did fine until Sept.. Who knows!

I hope you'll enjoy your beautiful trees for years to come.