Question
Hi, I have 15 arborvitae planted by a fence in April 2005 that have brown leaves and bald spots in the mid section and some bottom parts of tree. Tops of trees are green with lots of new growth.  Trees have southern exposure, watered regularly and small rocks at the base (vs mulch).  What is happening and what can be done to help trees?
Thanks

Answer
It sounds like a reaction to the site. You did not say how thick the rock "mulch" was around the trees. The main reason for mulch is to hold moisture and it also keeps weeds from growing around the tree and keep edger/lawn mowers away from the trunk. Mulch should not be more than 3-4 inches deep. Rocks add weight around the roots and if too thick can reduce the air spaces in the soil and cause the roots to smother. In addition to the extra time it takes to apply these materials, some consideration should be given to problems associated with replanting shrubs or removal of these mulch materials. Light colored materials will reflect sunlight and cause the temperature around the plants to be warmer. Rock mulch absorbs heat during the day and releases the heat at night thus increasing water loss.

Watering--water once a week with 1 inch of water if it does not rain. Put a pan under the tree and turn the sprinkler on when the pan has 1 inch of water in it stop.

Sounds like the heat from the rocks effected the lower part of the foliage and the water to the roots. But if the tree is putting on new growth and the upper foliage looks good the tree should recover but you might have less of  a thick foliage on the lower part of the tree due to the heat from the rocks.