Why Does Mulch Smell Like Manure?

Mulch begins to produce a manure-like smell when it is deprived of oxygen. When mulch is kept in large piles or stored in airtight bags, the bacteria that break down mulch create methane gas. A moist environment with poor air circulation traps this methane gas, resulting in a powerful manure smell. By spreading your mulch thinly and allowing it to dry, you’ll encourage your mulch to lose its manure smell in just a few days.

Why does mulch smell like manure?

What is Mulch Supposed to Smell Like?

Mulch that has been properly stored should smell like the material it’s made from. Straw mulch will smell similar to dry grass, while bark mulch should have a woody smell. Mulch made from pine should have a piny smell. Rubber mulches typically smell rubbery. If your mulch has a manure smell, this indicates improper storage.

Does Mulch Have Manure In It?

There is no manure in mulch. The smell of manure you’re experiencing when working with new mulch is due to Actinomyces, a type of bacteria that produces foul-smelling gases as it breaks down mulch. If the mulch has been stored in an oxygen-poor environment, these gases build up. That leads to an entire pile of mulch that has the strong odor of manure.

  • There is no manure in mulch.
  • Mulch is made of organic material, typically plant matter, which can have a manure-like smell as it decomposes.
  • The manure smell is caused by bacteria that are breaking down the mulch.
  • Manure smell is strongest if mulch has been stored in moist environments with little or no oxygen.
  • Sometimes, mulch can smell sour in addition to having a manure odor.

Other types of bacteria can produce ammonia in organic mulch. This will lead to a sour smell and increased acidity. So, if your black mulch smells sour in addition to smelling like manure, you most likely have a combination of methane and ammonia gases to blame. Don’t worry though—there’s no manure in your mulch.

How Long Does Manure Mulch Smell Last?

The manure smell of new mulch only lasts between 3–14 days. As mulch is allowed a chance to dry out and is exposed to oxygen, it will quickly lose its bad smell. To encourage the mulch smell to go away more quickly, spread your mulch out until it is no more than 3 inches (7.5 cm) thick. Then, allow it to dry. If you keep your mulch in mounds or piles, the smell will linger or may even become stronger.

  • The manure smell of new mulch typically lasts for 3–14 days after the mulch is spread.
  • Spread mulch in a 3-inch (7.5 cm) layer to encourage it to lose its manure smell more quickly.
  • Moist or wet mulch will retain the smell of manure longer.
  • Dry your mulch out on a tarp to get rid of the smell quickly.

Soil moisture also has an effect on how long the manure smell in mulch lasts. If your garden bed is wet, your mulch will have a hard time drying out. This can result in a long-lasting manure smell. To prevent this, dry your mulch on a tarp before spreading it in your garden.

Is the Smell of Mulch Dangerous?

Mulch that smells like manure is not dangerous to humans, animals, or plants. It may be unpleasant, but the amount of methane gas released by bacteria in your mulch is not enough to cause harm. Once you spread the mulch, the smell will dissipate until you can’t even notice it. The bacteria will still be hard at work though, breaking down your organic mulch into natural fertilizer for your garden.

  • Mulch smells are not harmful to humans or animals.
  • Organic mulch that smells like manure can be spread in your garden immediately without any harm.
  • Sour-smelling mulch can increase soil acidity and harm plants.
  • Spread sour mulch on a tarp and allow it to dry until it no longer smells bad, then use it.

If your mulch has a sour smell instead of a manure smell, it can be dangerous to your plants. Overly sour-smelling mulch indicates the presence of ammonia and high acidity in your mulch. Adding acidic mulch to your garden can increase soil acidity and harm your plants. So, if your mulch smells sour, spread it out and let it dry. Once it begins to smell like the organic material it’s made from, it’s ready to be spread in your garden.

How Do You Stop Your Mulch From Smelling Like Manure?

If your mulch smells like manure, the best way to get rid of the smell is to spread it in your garden. Spread your mulch in a layer no more than 3 inches (7.5 cm) deep. This will allow air circulation, which will quickly reduce the manure smell. If you leave your mulch in a pile or leave it sealed in bags, the manure smell will continue to build. The sooner you let your mulch receive oxygen, the sooner it will lose any unpleasant smell.

  • Encourage mulch to lose its smell by spreading it out in a layer no more than 3 inches (7.5 cm) thick.
  • Mulch loses manure smell once it receives exposure to oxygen and is allowed to dry out.
  • If you leave your mulch in piles or in bags, it will not lose its bad smell.
  • You can spread mulch in your garden bed or on tarps on your driveway.

Spreading your mulch out on a tarp is a great way to reduce the smell before you work with it. Dry conditions and plenty of oxygen help smelly mulch lose its stink. So, spread your mulch thinly across several tarps on your driveway and let it dry for a few days. By the time it’s dry, it will smell more like wood chips and less like manure.

Why Does Some Mulch Stink Like Manure?

If you’re wondering why your latest mulch delivery smells more like a barnyard and less like dry leaves or wood chips, here’s what you need to know:

  • There is no manure in mulch.
  • Mulch develops a manure smell due to bacteria that is breaking down the mulch.
  • When mulch is stored without oxygen flow (in bags or piles) the methane gas created by bacteria is trapped in the mulch. This produces the manure smell.
  • Mulch that is exposed to oxygen will lose its manure odor in 3–14 days.
  • Spread mulch in a 3-inch (7.5 cm) layer in your garden to encourage it to lose its manure smell more quickly.
  • If you want your mulch to smell better faster, spread it on a tarp on your driveway. Plenty of air flow and dry conditions make mulch lose any bad odors it may have.

Because the smell of mulch is harmless, there’s not too much to worry about. Your new mulch may smell unpleasant now, but this will only last for a short while. With a little bit of air and sunlight, your mulch will take on the scent of the organic matter it is made from.

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