Mulch has lots of benefits for your plants as it reduces soil erosion and helps the soil retain a healthy amount of moisture, but if your mulch smells like manure you may be alarmed.
The most common reason for this is due to either the organic or anaerobic decomposition processes that can take place, and it is usually a sign that something has gone wrong.
In this article, we will explore all of the reasons for mulch smelling like manure and what you can do to tackle this problem.
Technically, mulch is a layer of material that is applied to the top of soil. This means everything from wood chips to plastic sheeting can technically be considered mulch.
You may be wondering if your mulch actually contains manure. It is possible to use manure as mulch. However, manure is rarely what someone is referring to when they use the word mulch. In most cases, the smell is actually a result of decomposition, not manure in your mulch.
Mulch can be made from many materials. The most common types are organic and include leaf, bark, and wood chips. When it comes to man-made materials, rubber mulch is the most popular choice. You can also use compost as a mulch, or in conjunction with mulch.
Other natural materials that can be used as mulch are pine straw, moss, and grass clippings. Newspaper mulch can also be used.
As you can see, there’s a lot of variety when it comes to mulch. What is causing your mulch to smell will depend partly on the material it’s made from.
What Should Mulch Smell Like?
Mulch should generally smell like the material it’s made from. Bark and wood chips are the most common type of mulch. You can expect them to smell woody or earthy. Most other types of mulch should also give off an earthy smell.
Bad mulch, on the other hand, will typically smell like vinegar, ammonia, sulfur, or sewage. Depending on the type of mulch, it can also give off a chemical or rubber smell.
If the mulch has a vinegar, ammonia, or sewage smell, it shouldn’t be used in its current state. This is a sign there’s something in the mulch that can harm your plants.
Anaerobic decomposition means that the mulch is breaking down and doesn’t have proper airflow. This typically causes a manure, ammonia, rotten egg, or vinegar smell.
Because air is not moving through the mulch, the gases stay trapped, and then build up in the mulch. This is not only smelly. It’s also harmful for your plants.
Acetic acid or hydrogen sulfide are the culprits of the smell. They also cause the mulch to become very acidic. The ph can drop from an ideal 6 to a damaging 2 very quickly.
If you have organic material, like tree bark, wood chips, leaves, or grass, organic decomposition may also be the reason for the smell. This is caused by bacteria or fungus breaking down the organic material.
The most common cause of this is a type of bacteria known as Actinomyces.
They thrive in anaerobic environments. As the break down the mulch, they produce humus, water, and CO2. They also create heat. If your mulch feels very warm, this is likely the cause.
These bacteria can also cause a manure like smell. Despite the foulness of the odor, these types of microorganisms are good for your plants.
It should be noted that Actinomyces are an important part of the mulching process. The breakdown of the mulch releases nutrients that are good for your plants.
The smell shouldn’t be overpowering. It should have a mild manure smell.
Colored or Rubber Mulch
There are a few other reasons your mulch might smell, particularly if it’s a colored mulch or rubber mulch.
If you are using colored mulch, the color might be the reason for the smell. Red mulch is made with red oxide. It creates a rust type odor.
If the mulch is black, it’s likely created with carbon dyes. These shouldn’t have a strong odor.
Some mulch is treated with chromate copper arsenate, particualry if its made from old wood. This is a preservative that gives off an unpleasant smell.
Rubber mulch allows you to recycle things like old tires. Instead of ending up in a landfill, it can be used as a mulch for your yard or garden. Unfortunately, it tends to have a strong odor initially.
It will smell like new tires or sneakers. It’s a distinctive smell, but it should dissipate within a few days of installation. However, the smell may return with a vengeance during the summer, as the sun heats up the mulch.
Preventing Mulch Smelling Like Manure
The best way to handle stinky mulch is to prevent it from happening in the first place. To prevent a bad smell, you’ll need to store your mulch in a dry area with plenty of airflow.
Burlap or Open Containers
One way to prevent anaerobic decomposition is to store your mulch in burlap sacks or open containers. Unlike plastic storage bags or containers, these allow some air to flow through the mulch.
Fluff the Mulch
You can also fluff the mulch. This provides optimal airflow and allows air pockets to form in the mulch, which is beneficial for your plants.
Spread the Mulch
Spreading the mulch out on a tarp is a great way to store it. This allows it to breathe. Cover it with a weed barrier fabric. If this isn’t available, or you are concerned about moisture, use a roof tarp.
When stored in this way, mulch will stay fresh for months. Just keep it in a dry, well-ventilated area.
Storing Mulch in Original Packaging
If you must keep your mulch in the original packaging, poke a few holes in it. This will provide at least a small amount of airflow. Be sure it’s in a dry area.
Eliminating Manure Smell
If your mulch smells like manure, the fix is fairly simple. You’ll just need to give it plenty of air and sunlight.
Spreading Stinky Mulch
The best way to eliminate the smell is to spread the mulch out on a tarp. The area should be sunny and dry. You may need to check the weather forecast and plan for a time when there are several sunny warm days in a row.
The air and sun will eliminate the harmful chemicals that are created by the breakdown of the mulch. Be sure to turn it often as it airs out.
Fluff the Mulch
You’ll need to fluff your mulch about once a month. You’ll want to follow the steps above if your mulch has a strong smell. You can then fluff it monthly after applying it.
The mulch should be between 2 and 4 inches thick. A layer thicker than 4 inches is more likely to turn sour, because air can’t reach the bottom layers.
For indoor plants, poke holes in the mulch to improve airflow.
Can You Eliminate the Smell From Colored or Rubber Mulch?
One of the benefits of mulch is that when it breaks down properly, it provides extra nutrition for your plants. Unfortunately, rubber and colored mulch will not break down, and can even harm your plants.
Rubber mulch doesn’t provide any benefit for your plants, and the smell can be overpowering during the hot summer months. This is especially true if the mulch is exposed to a lot of sun.
Red oxide mulch is organic and perfectly safe for your plants. However, chemically dyed red mulches can release toxic chemicals and don’t break down as well as organic mulches.
Instead of attempting to remove the smell from these types of mulch, it’s best to just replace them with organic mulch. It’s really all you can do.
When Should Mulch Be Replaced?
You should replace your mulch yearly. As the mulch continues to break down, it can harbor bacteria that cause root rot. It also becomes more susceptible to mold over time, which can harm your plants.
Replacing your mulch once a year prevents these problems, and provides the best environment for your plants.
Final Thoughts on Manure Smelling Mulch
Unless your mulch is actually manure, it shouldn’t smell bad. Bad smelling mulch indicates a problem, typically anaerobic breakdown.
Do not use stinky mulch. Instead, allow it to aerate by spreading it out in the sun. Once the smell goes away, the mulch should be safe to use.
Prevent manure smelling mulch by storing it in a way that promotes airflow, and fluff the mulch monthly once it’s applied.