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Dog poop causes grass "burn" spots left in grass - Why does it do that?

Updated: Oct 11, 2022

Another reason to hire a service to pick up dog poop from your back yard is the grass damage and brown spots that can get left behind if you leave it to biodegrade on its own.

Poop Scooping grass burn
Grass Burn from Dog Poop

There is a lot of misinformation and incomplete information online regarding this phenomenon. When grass gets brown spots from dog pee or dog poop it is commonly referred to as grass "burn". This burn is NOT simply from decreased acidity or simply dehydration of the grass, or just too much nitrogen getting into the grass. More accurately, its actually a form of damage to the grass caused by osmotic pressure changes in the soil.


The nitrogen salts released from dog poop and pee into the soil ends up increasing the osmotic pressure of the soil outside of the grass roots, making it impossible/more difficult for the grass roots to take up water from the soil because the osmotic pressure within the root cells is lower than its surrounding environment (https://archive.lib.msu.edu/tic/wetrt/article/1976nov14.pdf ). This leads to the grass not getting enough water and other nutrients dissolved in solution in the soil, and in more extreme circumstances can cause root damage and cell death, causing the grass to die. It usually manifests itself visually at the start by the grass tips turning brown, but eventually the whole grass area can turn brown.


Its not altogether unreasonable to assume that dog poop might be a good fertilizer though. After all, many popular natural fertilizers like cow manure and bat guano serve as important fertilizers. Indeed, dog poop does contain high amounts of the standard fertilizer component nitrogen, and if it were applied deliberately and in the appropriate concentrations, it could indeed act as a fertilizer. However, there are some fundamental differences in the composition of dog poop, and the localized manner in which its contained nutrients are applied and released as compared to cow manure.


First of all, dogs are mainly carnivores and as such their diets contain much higher concentrations of proteins, which increases the concentration of nitrogen based, and other salts, in both their pee and poop, as contrasted to herbivores like cows. So when a dog uses the bathroom in your yard, these concentrated nitrogen salts are able to change the osmotic pressure of the soil more vigorously. When dogs pee, the urea gets applied in a very concentrated area immediately, and when dogs poop and the poop sits there to break down over days or weeks, the area directly around the poop pile also gets a somewhat slower dose of nitrogen salts and concentrates in the local soil over time. The end effect is a higher localized concentration of nitrogen, which leads to osmotic pressure changes in the soil just around the brown spots that cause the grass "burn" brown spots. You might also notice though, that sometimes there is also a small ring of grass around the grass burn perimeter that is extra lush and greener and taller. This is because at the right concentrations (lower) and moisture conditions, dog poop actually does serve as a fertilizer making your grass grow better.


There are some other closely related factors that can help mitigate, or worsen this grass burning issue. Because osmotic pressure is an issue of salt concentration, if you simply water your grass in the affected brown spot areas, you may be able to affect a positive change in your grass health by diluting the salts, allowing the grass to take up more water again. However, this solution is time dependent. If you can water your grass/soil before any permanent damage has been done to the roots for instance, you will make more of a difference. This can be difficult to do frequently and soon enough though, because studies show that grass can be damaged in as little as 8 hours after nitrogen from dog pee or poop enters the local soil. Regular watering of your grass should help prevent some of this grass burn regardless. On a similar note, how often it rains in your area will help determine the moisture content and osmotic pressure considerations in your back yard, as will the manner in which your yard's drainage is set up. Finally, even if nitrogen from dog poop is helping your grass grow greener and not causing grass burn short term, in the long term this over fertilization can lead to overgrowth and too fast of growth, which can cause cross hatching, and overgrowth of grass roots which leads to other problems like poor oxygen and water availability in the soil and more susceptibility to stresses like heat, water stress, and pests.


As you can see, the threat of stepping in dog poop isn't the only reason you should consider hiring a dog poop scooping service. It can also help keep your lawn healthier in the long term. If you're in the Houston area, give Doody Bug a call at 346-225-5144 if you have questions about our service.



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