Q: Can you identify what’s killing my Emerald Green arborvitae trees? The trees would first get small patches of gray/brown needles. Then, the browning spreads until it consumes the tree. Can you identify what is causing this issue?
A: It looks to me like the root ball dried out at some point. In my experience, arborvitae cannot stand having dry roots. This can be a real problem if arborvitae is planted in the spring.
We all know what type weather comes after spring. Just a couple of days of hot weather can absorb all the water in a newly-planted arborvitae‘s root ball.
In my experience, arborvitae should always be planted in the fall so there’s not so much water stress during winter. Roots can easily grow and explore the surrounding soil, giving them more area from which to absorb water.
The best way to plant them is to loosen soil in an area six feet in diameter. Remove top six inches of soil and pile nearby
Then remove as much soil from the tree root ball as you can. Spray the roots with water as you work. Spread the roots out widely in your initial hole and backfill over the roots with the soil you removed.
Water deeply once a week….. or twice a week if it is windy or the temperatures are high.
Continue for at least three months. If your soil is mostly red clay, extend the watering until cool fall days arrive.
Watch for the gray patches of needles next year and water the tree immediately.