rust coloring on emerald green arborvitae

Asked May 20, 2013, 1:08 PM EDT

we have 35 emerald green trees lining our driveway they are well established about 7 yrs old , this spring they are turning a rust color on the north side of the tree. the discolored area does not feel brittle at all we are wondering if that will go away? we have watered deeply and put a good fertilizer down that is high in iron. We are concerned that they might die. thanks for any help or ideas. Sincerely, Mary

Larimer County Colorado

1 Response

Hi Mary,

It's likely not due to lack of fertilizer, but because of our dry winter, windy conditions and the fact that this plant tends to do better in high humidity climates. The north side of plants tends to receive the greatest amount of wind and since this plant is an evergreen, it is losing moisture all year round. While fall and winter watering helps, it may not be enough to compensate for the amount of transpiration that occurs during our bright, sunny days.

It could have been the dry winter, or another thing to consider is the late spring freezes we had. On May 1, the night temperature dropped to 17 degrees...right when many plants were pushing new growth. The new growth is very tender and isn't hardy or tolerant to freeze injury.

Unfortunately, when evergreens brown, they usually do not recover or turn green again...but we're learning many new things this spring. I would adopt a "wait and see" policy. You could wait to see how they recover and then consider pruning out the dead branches, if it doesn't cause the shrubs to look unsightly.

If you do lose them, there are other options to consider, like upright junipers, which are more tolerant to our Colorado conditions and come in many colors, shapes and sizes. CSU also has a publication on "Evergreens for home gardens" found here: http://www.ext.colostate.edu/pubs/garden/07414.html