There are many factors that can cause evergreen trees to lose needles. Perhaps the most common in our area are improper watering--either too much or too little--and damage from cold and/or drying winds.

Drought conditions together with cold temperatures and drying winds can be very harmful to evergreen trees. Because they keep their needles year-round, evergreen trees are still transpiring, and therefore still need to be watered regularly during the winter (all trees require some winter watering to stay healthy).

Drought conditions and drying winds make evergreen trees more prone to cold injury, and this last winter was marked by some unusually cold temperatures. This damage may not show up until later in the spring. The fact that the needles dropped and then grew back suggests that this may be the issue.

There is no cure for drought or cold injury. Provide deep, regular watering throughout the year. Avoid the urge to over-water as this can also cause the same symptoms. The soil should be consistently moist, but not soggy. Applying and maintaining a 2-3 inch layer of mulch beneath the tree will also help conserve soil moisture and moderate soil temperatures.

Heat reflected from surfaces such as concrete driveways and sidewalks, fences, and other structures can also cause damage. It appears from the photos that this tree is planted very near the house. This might also be a contributing factor.

If you still think your tree may have an insect or disease, or other problem, you can call the Broomfield County Master Gardener Hotline and arrange to bring a sample in:<personal data hidden>.

For more information, here are some links to some helpful fact sheets from CSU Extension:

Environmental Disorders of Woody Plants

Fall and Winter Watering