Question:  Can night lighting disrupt the growth of trees?

The February 1994 Tree Care Industry contained a most interesting and informative article on “Lighting the Landscape.” “Nightscaping” can be a profitable venue but it is not without its pitfalls and, if not approached with a high skill level, can and does end up with disastrous consequences.

Night light can easily disrupt the growth of trees. In the buds and leaves of trees are located “eyes” called phytochrome; they respond to the red portion of the light spectrum. It is phytochrome that tells a tree when to go into dormancy. Night lighting can fool a tree into thinking days are longer than they actually are. A tree can continue growing during normal dormancy periods, making it more susceptible to freezing temperatures. The formation of chlorophyll in leaves is also inhibited. Yellowing of leaves can occur. Night lights can drastically change the bloom cycle, the amount of blooms and create long spindly branches. Some trees have a high tolerance to night lighting while other species do not. Sensitive trees, such as dogwood, red bud, yellow poplar, black locust, silver bell and others, will need a higher degree of maintenance including more water and fertilizer. Insect and disease problems must be more closely monitored. If a tree must be continuously and directly lighted, use a light source that is low in red light such as mercury vapor lamps. High pressure sodium and incandescent filaments are rich in red light and will greatly alter the growth of a tree. In conclusion, one of the most important lights in nightscaping should be the caution light.

Author: Joseph R. Samnik, Certified Arborist