Ask Mr. Smarty Plants

Thank you for writing! The condition you describe sounds like winter injury, although there could be other causes as well. Here's what I think probably happened. Because your arborvitae is right next to a brick wall the conditions in the foliage of your plant within a few inches of the wall can be quite different than the conditions on the other side of the plant. Brick walls act as heat sinks, that is, they store heat on sunny days and radiate the stored heat at night or when it gets cloudy. The net effect for your arborvitae is that the foliage next to the wall probably did not acclimate to the colder conditions at the beginning of winter and was susceptible to freezing injury on the first really cold night of winter. If that night followed a sunny day, the effect would be especially pronounced. Very cold, very sunny days can have dramatic affects on even cold-hardy plants. Water stress at that time would exacerbate the problem. It is always a good idea to water your plants before a hard freeze if it occurs after a period of little or no rain.

There are some diseases that affect arborvitaes. Here is a link to a Penn State website with a very good section on Arborvitae Diseases. If you suspect a disease or insect problem I recommend taking a limb that includes both the affected area and some living tissue to your county extension agent for diagnosis.

I would not recommend using "nutrient spikes". In fact, you should never feed a stressed or diseased plant. It sounds like you have rich soil. Adding some compost when the plant begins to show new growth should be all your plant ever needs.