Q & A: Grass Scald
By Dr. Kim Everson, DVM
Question: Every spring my lawn has lots of brown spots where my dog urinated. What can I do to prevent this from happening?
Answer: That is a very common and frustrating problem. It is such a common complaint, in fact, that pet stores carry numerous treats, vitamins and supplements that promise to prevent yellowing of your lawn by changing your pet’s urine. The big question is do they work? And are they safe?
The actual cause of urine scald is heavily debated. A common belief is that urine with an alkaline, or basic, pH is the culprit of grass-kill. The proposed solution is to acidify the urine by feeding the pet compounds like dl-Methionine or vitamin C (ascorbic acid). How well these vitamins and supplements work to acidify the urine probably depends on the dog. In order to determine if a urine acidifier is working requires multiple urine pH checks by your veterinarian before and after starting the product. Some dogs have serious medical conditions that may worsen if their urine is acidified, so be sure to check with your veterinarian before starting any new supplement.
Whether or not acidic urine reduces lawn burn has not been proven. A more likely explanation is over-fertilization of the area with the nitrogen wastes present in the urine and, to a lesser extent, feces. The kidneys rid the body of excess nitrogen (a product of protein metabolism) by concentrating it in the urine. While feces also contain nitrogen waste, the nitrogen is more slowly released into the surrounding grass. This is why you get a small dead spot surrounded by a lush ring of grass where stools sat on the lawn.
In small amounts nitrogen is a fertilizer, providing nutrients to the grass to stimulate growth. However, dousing the lawn with nitrogen-rich urine puts the grass completely off kilter. While a small amount of nitrogen is required by plants to live, an excess amount interferes with root development, causes dehydration, and essentially sterilizes the plant causing browning and plant death. Interestingly female dogs cause more lawn scald than males because they empty their bladder in one spot on the lawn whereas male dogs mark in multiple locations. However, similar damage to shrubbery and ornamental plants can occur if male dogs over-mark on those plants.
In response to this theory of lawn scald, lawn care companies have created supplements for pets that basically dilute the urine to reduce the amount of nitrogen present. This might be done with herbal diuretics or salts that stimulate drinking and promote dilution of the nitrogen in the urine, making it less potent. Again, it is a good idea to check with your veterinarian before starting such a supplement, especially if your pet has a known medical condition.
A very safe but more time consuming alternative to diluting your pet’s urine through the use of supplements is to follow along behind your dog and saturate the spot where she or he urinated with water from a garden hose, gallon jug or bucket. Doing so will dilute the nitrogen-rich urine making it less toxic to the grass. Also it will allow you to build muscles while enjoying the outside air this spring and summer!
Originally printed in Pet Journal, September 2014