Gardening Q&A: Spruce tree may be suffering from leaf scorch

Q: Help! The large blue spruce in a narrow planting bed next to my driveway is starting to lose interior needles, especially on the side of the tree facing the concrete. Needles turn brownish and dry before falling off. The other side of the tree facing the lawn looks normal. What’s going on?

By Nika Reininger
Colorado State University Extension Master Gardener in Larimer County

A: Your spruce tree may be suffering from leaf scorch. Leaf scorch occurs when a tree loses water faster than can be absorbed by its roots during hot summer weather. In evergreens, leaf scorch is characterized by changes in needle color, followed by needle loss in severe cases. While this can be caused by a variety of factors, including overwatering and overfertilization, in your case the pattern of symptom distribution is revealing.

The narrow planting bed located next to your driveway may be to blame. When large trees are planted in an area in which their root development will be restricted (such as next to a driveway or parking lot), it limits the tree’s ability to take up water from the soil. The spruce roots nearest the driveway are responsible for supplying water and nutrients to branches on that side of the tree. Therefore, if root growth or water uptake is limited by hardscape areas, damage will often be first visible on that same side of the tree, especially in hot conditions. Needles on the branches facing the lawn may appear healthier, because the roots associated with those branches have plenty of space to grow and can absorb water from the turfgrass area. Hardscape areas not only restrict root growth and limit water absorption; they also reflect heat and light back onto the tree, further contributing to heat stress.

Unfortunately, existing damage to needles cannot be reversed. Further damage may be prevented by addressing the tree’s cultural requirements. Ensure that the soil is well-drained, and give the tree deep, infrequent waterings, moistening the soil to a depth of at least 6-8”. If the tree’s root system is only receiving irrigation on the turf side, it may be useful to install a drip system on the dry side of the tree near the hardscape. Apply mulch to conserve water and aid in lowering the soil temperature around the tree’s roots. Choose an organic mulch material, taking care to keep the mulch away from the tree’s trunk. Winter watering is critical in our dry climate, especially for evergreens that continue to transpire water through their needles year-round. Blue spruce (Picea pungens) is native to cooler mountain areas featuring higher soil moisture levels than lower elevations. These trees can become quite large, growing up to 60 feet tall and 25 feet wide.

Therefore, a full-sized spruce cultivar may not be the most appropriate long-term choice for a restricted planting bed next to a driveway.

For more information, see the following Colorado State University Extension publications:
“Leaf Scorch.” Fact Sheet #2.911: www.ext.colostate.edu/pubs/garden.