What should I do before planting arborvitaes again in the same place.

Asked March 18, 2019, 12:56 PM EDT

I have a row of 20 arborvitaes, but 3 of them died right next to each other. When I removed them, the roots were rotten and they came out easily. It also looked like some kind of bug might have been the problem.

Clackamas County Oregon arborvitae

1 Response

Thank you for using Ask an Expert for help with your arborvitae hedge.

One of the biggest challenges these plants face in our area is wet soil. They can be attacked by a root rot that gradually destroys the plant’s root system in a similar way to what you described. This fungus is commonly present in the soil, but only becomes active when the plant is growing in or exposed to poor drainage.

This section of the hedge may be in a lower part of the yard, where water tends to collect. Or perhaps it is an area where sprinklers put out more water than at the other end of the line of plants. I also notice that the grass on the far side of the fence is green. The watering your neighbor does may be affecting the root system in this part of the yard. I also noted that the remaining arborvitae, on the right, seem to be thinning, which may indicate a continuing problem.

The important thing, if you decide to use the same plants, is to ensure good drainage. Correct any drainage problems you find, change any problematic watering patterns, or plant the new plants a bit higher (four to six inches) than the surrounding soil level. In addition, the variety ‘Pyramidalis’ is considered somewhat resistant to the root rot disease.

The holes you see in the trunk of the arborvitae appear to be one of the borers that attack the arborvitae family. These insects are attracted to plants that are already stressed, which your trees probably were. Give the new plants a good start and good care, and they will be able to fight off these pests.

For more on tree care, see the publication “Selecting, Planting and Caring for a New Tree”, either the video or a printed copy, here: https://catalog.extension.oregonstate.edu/ec1438

Have a good gardening year,