I have two female dogs whose urine was killing patches of grass all over my lawn. On my mother鈥檚 advice I started feeding them tomato ketchup and, sure enough, the dead patches stopped appearing. Why does this work, and is it harming my dogs?
The urine acts as a liquid fertiliser, but can produce nitrogen overload where the puddle of urine is deepest. This 鈥渂urns鈥� the grass, creating a brown patch in the lawn.
Towards the outside of the puddle, where less nitrogen has been applied, there can be a fertilising effect leading to a ring of luxuriant, greener grass. The urine of dogs and bitches does not differ much but, while dogs tend to deliver small samples of urine to mark their territory, bitches tend to empty their bladders entirely, causing more harm.
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Urine is slightly acidic, but so is tomato ketchup, so it does not neutralise the urine as some people believe. Instead, the salt content of tomato ketchup, juice or sauce makes dogs drink more, diluting the nitrogen in their urine.
Be aware that increased salt intake can cause problems with existing kidney or heart conditions, so if you must tinker with your dogs鈥� diet, consider reducing the protein content instead. This will also reduce the nitrogen content of their urine, and should be fine for all but the most active of dogs. Better still would be to train your dogs to urinate in a designated place or follow them out of the house with a hose pipe or watering can to dilute their urine.
Mike Follows, Willenhall, West Midlands, UK