How Long Is an Unopened Bag of Mulch Good For?

I use mulch to add nutrients to my garden, improve soil cover, and enhance the garden beds’ looks to make the area more attractive. However, it’s important to carefully store this mulch to prevent hastened decomposition, pest infestation, and mold growth. Still, how long can an unopened bag of mulch survive in storage without losing its viability?

An unopened bag of mulch is good for about three to twelve months, provided it’s dry and contains no holes. While it’s impossible to halt mulch decomposition, a poorly stored bag will decompose faster than an adequately stored bag of mulch.

In this article, I’ll explain how you can best store mulch and help you understand factors that may accelerate the material’s decomposition. It’s also essential for you to learn how to tell if your mulch has expired or gone bad. Let’s get started!

Do Bags of Mulch Expire?

Mulching is an immensely beneficial practice, and it’s been used in gardens and farms worldwide for hundreds of years. Mulch protects your plants, helps the soil retain water and nutrients, and improves your garden’s general look. 

The material is usually made up of organic materials like wood chippings, compost, and cedar chips. However, despite its benefits and natural composition, mulch expires. This shelf life is largely because of the material’s organic composition.

Still, you can store bagged mulch—mostly made of bark—for up to a year. But you can slightly extend this expiry period if you improve storage conditions. However, you have to ensure that the weather is appropriate too.

Heat can also accelerate the decomposition of mulch, even if the material is not exposed to air or water.

The decomposition process is initiated by microbes like bacteria and fungi that live in the mulch. These organisms feed on all the dead matter they can to stay alive.

And while the decomposition process is faster for opened and spread mulch, it’s much slower if the bag stays unopened.

How To Know if Your Bag of Mulch Has Gone Bad 

As I’ve mentioned, many factors contribute to the decomposition of mulch. And you’ll notice it starts going bad after storing or spreading it for a while. Therefore, whether you use wood chippings or alternative organic materials for your mulch—the decomposition process happens all the same.

Here are some ways to know if your bagged mulch has expired and gone bad:

  • Terrible smell
  • Presence of mold
  • Insect infestation
  • Signs of anaerobic decomposition

Let’s explore these signs in detail.

Terrible Smell

Mulch typically smells like earthy soil and freshly cut wood. On occasion, healthy mulch can also smell like fresh compost during aerobic decomposition—a breakdown process that occurs in the presence of air.

Still, it’s possible to have mulch with faint unpleasant odors—and that’s usually not a cause for alarm.

However, mulch that’s starting to go bad smells like rotten eggs, ammonia, vinegar, and even manure. This terrible smell is caused by anaerobic decomposition, which occurs in a limited air supply and releases excess Nitrogen and similar minerals.

Commercial mulch is usually stored in large piles after it’s been processed. This storage method typically leads to material compression, which may initiate anaerobic decomposition in mulch—even before the product leaves the factory.

Airtight bags might further accelerate this process, making some mulch unfit for use within three months of purchase.

Fortunately, some manufacturers store their mulch better during the production process. This improved storage results in slower decomposition rates and less terrible smells.

I need to note that using sour and terrible-smelling mulch will hurt your plants and damage your garden but it’s not usually harmful for people. Bad mulch typically kills plants it comes in contact with, but it might also result in stunted development.

Presence of Mold

You might also find mold in bags of bad mulch. However, you’ll usually find them thriving in organic matter. These unwanted molds develop due to high levels of humidity and excess amounts of sunlight.

Interestingly, wood chips—one of the most commonly used materials for mulch—is a significant food source for most mold species. Therefore, it’s no surprise that it’s common for bags of mulch to develop mold the longer they sit in storage.

Damp storage areas also massively contribute to the emergence of mold. These areas have a lot of humidity and moisture—perfect for hastening decomposition.

Sunlight and warmth can also make your mulch start to grow mold. In fact, temperatures between 77 and 86°F (25 and 30°C) are perfect for mold growth.

Therefore, while mold species need organic matter to grow, they’ll only thrive in areas with abundant moisture and sunlight. And although mold doesn’t significantly affect mulch, it can make mulch look unattractive.

Insect Infestation

Mulch naturally attracts decomposers and insects like worms, millipedes, termites, spiders, and cockroaches. These organisms like mulch because it contains lots of organic matter to feed on and offers shelter for others.

However, you’ll find that these decomposers often infest bad mulch—making the material more difficult to use in gardens.

And while the presence of these insects might not always be bad, these infestations can lower the quality of bagged mulch and accelerate the decomposition process.

Signs of Anaerobic Decomposition

Aerobic decomposition is essential for mulch to release its nutrients into the soil. However, it will undergo anaerobic decomposition if it doesn’t get enough air. Anaerobic decomposition can damage bagged mulch, but the affected mulch can cause stunted growth or death if you spread it on the soil.

What’s the Best Way To Store Mulch?

You must prevent mold growth, fungi outbreaks, and insect infestations when storing mulch. However,  you must also focus on reducing or eliminating terrible smells and preventing leaching.

Here are some ways to best store mulch:

  • Ensure the storage area is well-ventilated.
  • Keep in a cool, dry place.
  • Pour out unused mulch onto a tarp.
  • Dry your mulch occasionally.
  • Transfer your mulch to a plastic container

Let’s see how these methods work.

Ensure the Storage Area Is Well Ventilated

Well-ventilated rooms or storage areas are necessary when trying to store mulch. However, the absence of air might make the material decay much faster due to anaerobic decomposition.

Therefore, you must keep the mulch in an area where it can get a lot of air—especially if you’re storing it for extended periods.

Remember to poke some holes in your bagged mulch if it doesn’t have any if you want it to last longer. Poking holes should be relatively easy since most bagged mulch come in plastic sacks. I recommend you make these holes in strategic areas that ensure air gets into the bags.

This storage method is especially effective if you’re storing the mulch for a few days or weeks.

Keep in a Cool, Dry Place

You can’t store bagged mulch for extended periods under sunlight or hot conditions. This environment will make the material develop mold, harmful bacteria, and dangerous fungi.

Instead, try to keep your mulch in a cool, dry area. This practice will protect your mulch from excess sunlight. It’s also an excellent way to prevent your mulch from retaining moisture.

Pour Out Mulch Onto Tarp

As I’ve mentioned, bagged mulch usually undergoes significant compression after manufacturing. This storage condition shortens the product’s lifespan and increases the likelihood of anaerobic decomposition.

Tarps provide a protective layer to correctly store your mulch by spreading them out. Spreading your mulch on a tarp allows the material to breathe without affecting the natural decomposition process.

You can also spread another tarp over the newly-poured mulch to prevent moisture retention from rainfall or the atmosphere.

Dry Mulch Out Occasionally

Despite your best efforts, mulch will always generate moisture from the natural decomposition process. But you can always dry out the bags if you want to prevent that decomposition-derived moisture from reducing your mulch’s shelf life.

A tarp is best for drying your mulch out. Lay the tarp on the ground to provide a space for spreading your mulch, and try to spread mulch as thin as you can.

While it will continue to decompose, the process will proceed slowly and with excess air.

Drying your mulch out is also crucial to slow the effects of anaerobic decomposition. In other words, it will make your mulch smell a lot less and help prevent the leakage of essential nutrients.

Transfer Mulch To a Plastic Container

For long-term storage, an alternative method of storage is to use a plastic container. This container must have holes, and you can place it in a cool, dry area. Like tarps, plastic containers help store mulch while providing adequate oxygen to the material.

To recap: while you can store bagged mulch for quite a while, it does not last forever. After being kept in piles for about three months, decomposition and other natural processes will occur—resulting in peculiar odors and mulch degradation.


I recommend you spread it on your soil within three months of purchase to ensure you get the most out of the material. Ensure to spread evenly on your soil’s surface.

This process will help you save money, but it’s also a more effective way to use the mulch in your garden. 

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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