How long does dog poop take to break down?

It's tempting to let nature handle it. Poop is organic, so it has to go somewhere, right? It does, eventually. The catch is how long "eventually" takes, and what a pile leaves behind once you can't see it anymore.

Does dog poop decompose?

Yes, eventually. USDA NRCS puts it simply in its backyard composting guide: all organic matter eventually decomposes, with bacteria, fungi and other small organisms doing the work.

But breaking down isn't the same as going away safely. A pile on the lawn never heats up the way a managed compost pile does, and NRCS notes that slow, cool piles may not get hot enough to kill disease-causing organisms. The same guide tells home composters to keep dog and cat manure out of the bin entirely, because it can carry disease.

That's why the EPA counts the belief that dog waste will "take care of itself" among the misconceptions that lead people to leave it on the ground.

How long does dog poop take to decompose?

There's no reliable single number. Search online and you'll find confident ones, but we looked for a figure from a government agency, a university or a veterinary source and didn't find one. So instead of a number we can't back up, here's what speeds a pile up or slows it down.

NRCS says decomposers need four things: nitrogen, carbon, moisture and oxygen. The weather decides how well they get them.

For scale, NRCS says a hands-off compost pile of grass clippings and leaves can take several months to a year or more to break down, depending on what's in it and the conditions. A pile on your lawn gets no turning, no mixing and no help at all.

Around here, the season matters as much as anything. Detroit's normal high is about 84°F in July and about 32°F in January, according to the National Weather Service. A pile dropped in July and one dropped in January live very different lives, which is one more reason a single number can't fit a Michigan yard.

Does dog poop dissolve in rain?

No. Rain can soften a pile and break it apart, but the pieces don't disappear. They move. The EPA says stormwater picks up pet waste left on the ground and carries it into streams, lakes and rivers, directly or through storm sewers. There, it can make people and animals sick and promote weed and algae growth.

In Macomb County, that trip ends at Lake St. Clair. County Public Works maintains 475 county drains, and all of them eventually carry storm water to the lake. From April through September, the county Health Department checks the water at five public beaches for E. coli. A state cleanup plan for two of them, Lake St. Clair Metropark and Memorial Park, names pet waste as one possible source of that E. coli (Michigan EGLE). Our guide to dog poop and Lake St. Clair follows that path from yard to lake.

And don't try to speed things along with the garden hose. Water just pushes waste toward the street and the drains, and Macomb County Public Works asks residents to keep pet waste away from drainage ditches and storm drains.

Whatever the rain leaves behind ends up in your soil. That's where the longest-lasting problem lives.

Why do parasite eggs outlast the pile?

Because they're built to. The CDC says roundworm eggs passed in dog poop need 2 to 4 weeks in the environment to become infective, and a strong protective layer lets them survive for months, or even years, under the right conditions. By the time a pile has crumbled into the grass, its eggs may just be getting started.

One reassurance: the CDC says you're unlikely to catch Giardia from a dog, because the type that sickens people usually isn't the type that sickens dogs. Roundworm is a different story, and its 2-to-4-week clock is why a regular schedule beats waiting. A pile picked up within days leaves its eggs little time on your lawn. Here's how often to pick up dog poop for your pack.

What happens to dog poop in a Michigan winter?

Mostly, nothing, until spring. University of Vermont Extension explains that cold air pulls heat out of a compost pile until its decomposers slow way down or, if the pile freezes, stop altogether. A pile on a frozen lawn is in the same spot. With January's normal high right around freezing, and a normal season bringing about 45 inches of snow, most of it in January and February (National Weather Service), piles freeze, get buried and wait.

Cold doesn't wipe the slate clean, either. In a lab study, dog roundworm eggs survived six weeks at 1°C and -2°C (about 34°F and 28°F), then still developed to the infective stage once they warmed up (Azam and others, 2012). That's one study, not a backyard, but it's reason enough not to count on winter.

Then comes the thaw. The EPA defines stormwater runoff as water from rain and snowmelt that flows over the ground instead of soaking in, so a winter's worth of piles meets the melt all at once. We keep scooping through the winter, picking up everything above the snow and catching up when it melts. Our winter guide has more.

Should you just wait for it to break down?

No. Pick it up. The CDC's advice is to pick up your pet's waste every time and bury it or bag it for the trash. Its guidance for dog owners says to do that even in your own yard, especially where children may play. And the Macomb County Health Department asks residents to routinely clean up pet waste and put it in the garbage.

A simple routine beats waiting:

1. Grab what you see every time the dog goes out.
2. Sweep the whole yard at least weekly, corners, mulch beds and fence line included.
3. Bag it and trash it. Never rinse it toward a storm drain, and keep it out of the compost pile; here's why it isn't fertilizer.
4. Wash your hands with soap and water when you're done.
5. In winter, pick up whatever sits on top of the snow, then clean up quickly at the thaw.

If keeping up is the hard part, that's our job. Poopy Scoops walks the whole yard in a grid, double-bags every pile into your outdoor trash can, and texts a gate-check photo when we're done. Weekly visits are $19 for one dog. Get your price in about 30 seconds.