If a dying cedar tree is a recent transplant, the problem is often with the planting method. When more established trees die, pests and drought are often the cause.
Many homeowners wait too long after purchasing their trees to plant them in the ground, allowing the root balls to dry out, which prevents the trees from growing new roots and ultimately causes them to die. Adding too much dirt over the root ball when planting causes the tree to die from a lack of oxygen. Trees left in the pot too long before transplanting grow roots in a circular pattern; this effect is called girdling. The girdled root ball never spreads outside the original planting hole, and the tree dies from a lack of water and nutrients.
Cedars are susceptible to pests ranging from insects, such as the white cypress tip moth, to larger animals, including mice. Pets may also damage them. Moths cause the foliage to turn from green to brown. Larger animals often eat the bark from the base of the tree. If the damage is limited, one side of the tree usually dies. If the animal eats most of the way around the circumference of the tree, the entire plant dies.
According to USA Today, thousands of trees, including white cedars in Indiana, died as a result of drought from 2010 to 2011. Trees continued to die from the effects of the earlier drought two years later.