Canine, or dog, urine can cause evergreen trees' and shrubs' low foliage to turn yellow and then dark brown or black. In most situations, dog urine doesn't kill evergreens. If, however, the plants are subjected to dog urine frequently, then eventually the urine can affect their health. Certain measures, though, can prevent or reduce dog urine's damage to evergreens.
Dog Urine's Effects
Dog urine contains urea, which is produced as a waste product when protein is metabolized in the body, and it is excreted along with other salts in the dog's urine. Urea is a nitrogen compound that is used in fertilizers because in soil it is converted to nitrates, which are the primary form of nitrogen used by plants. The urea in dog urine isn't beneficial to plants because its concentration is too high, which creates an environment in which water is drawn out of plant cells.
Other than installing a fence, not much can be done to prevent a neighbor's dog from urinating on your plants. If your dog is the source of the urine, then modifying its diet may prevent the urine from damaging your evergreens and other plants. Feed the dog low- to moderate-protein foods instead of those labeled as high in protein; less protein reduces the amount of urea in the urine. Also, high-quality proteins are easier to digest, which means less urea is excreted in the urine. Typically, dog foods labeled as premium and super premium and that are available at pet stores and veterinarian offices have higher quality proteins than most brands available at grocery stores, but consult your dog's veterinarian before making changes in the dog's diet.
If you can't change your dog's food, dilute the dog's urine by adding water to the canine's food, using canned dog food or increasing its daily water intake. Your dog may need to go outside to urinate more often than previously, but its urine will be less likely to burn your evergreens and other plants.
Urine-damaged evergreens are not a lost cause, although their discolored foliage may not regain its green color. If you see the dog urinating on the plants, immediately rinse the plants with water to dilute the urine, which can prevent damage. If damage has occurred, water the ground around the plants, which leaches the salts from the soil. You may have to repeat watering as the soil dries to leach heavy salt buildups caused by frequent or long-term urination on the plants.
Plants that have a high salt tolerance may be able to withstand dog urine's salts better than other plants. Salt-tolerant evergreen trees include Chinese juniper (Juniperus chinensis), which is hardy to U.S. Department of Agriculture (USDA) plant hardiness zones 2 through 8, blue spruce (Picea pungens), which is hardy to USDA zones 2 through 7, and mugo pine (Pinus mugo), hardy in zones 2 through 7. Evergreen shrubs that have a high salt tolerance include serviceberry (Amelanchier canadensis), which is hardy in USDA zones 3 through 7, Japanese barberry (Berberis thunbergii), hardy in zones 4 through 8, cottoneaster (cotoneaster spp.), hardy in zones 4 through 8, and Russian sage (Perovskia atriplicifolia), which is hardy in zones 5 through 8.