Mulch is one of the best things that could have happened to home gardening.

It helps to keep the soil moist and cool in the summer while preventing frost heaving in winter, inhibits the growth of pesky weeds, provides your plants with a much-needed bevy of nutrients, and makes your garden look neat and tidy, all for very little cost.

Mulch is great. However, sometimes you will find that mulch smells, quite frankly, like rank manure or something spoiled and rotten. 

Foul-smelling mulch is unpleasant to be around and can end up harming your plants. So, in today’s post, I’m going to tell you why your mulch smells bad and, most importantly, what you can do to fix it.

Why Does Mulch Smell Like Manure?

Mulch smells like manure because the organic material with which it was made has begun to decompose. Decomposition of organic material results in elevated concentrations of hydrogen sulfide, methanol, and acetic acid, all of which have strong and unpleasant odors.

When it comes to mulch, the main source of decomposition is a lack of oxygen and the resulting anaerobic bacterial activity.

What Is Mulch Supposed To Smell Like?

Good mulch should smell of wood or damp earth, it may even have a slight aroma of fresh compost. It shouldn’t be unpleasant and it shouldn’t smell like anything rotten at all.

This fresh, natural smell is one of the easiest and quickest ways to tell if a batch of mulch is worth adding to your garden. If you catch even a slight whiff of a smelly sour odor in your mulch, then you should discard it and get a different batch.

Good mulch should smell of wood or damp earth

Why Is It Important To Use Fresh Mulch?

Good mulch is highly beneficial to your plants, but if your mulch smells bad it is more than likely to be harmful to your garden.

Bad mulch, that is mulch that smells rotten, can literally poison your plants and provide them with toxins instead of nutrients. These toxins include things like methanol, ammonia, alcohol, acetic acid, etc., and they can quickly spread through the soil and reach the nearby roots.

One of the first signs of having bad, toxic mulch is dying leaf tissue. If you notice that the bottom leaves of your plants are turning yellow soon after mulching, and this is accompanied by a foul smell, you should quickly remove the mulch completely to prevent further harm.

If you catch the bad smell before any yellowing starts to spread you may be able to save your mulch by contrasting the anaerobic action.

How To Fix Bad Smelling Mulch?

If you attack the problem early on, before the toxins released by decomposing mulch have had time to cause irreparable damage to your plants, you may not have to get rid of your mulch to fix the issue.

It Is Important To Use Fresh Mulch

Since the primary mechanism which causes mulch decomposition, and its resulting gross stench, is an anaerobic bacterial activity in a low oxygen environment, you can easily revert the process by reintroducing sufficient oxygen into the mulch.

To do so, remove the stinky mulch from your flower beds and thinly spread it across a plastic canvas or tarp, making sure that all of the mulch material can breathe.

Let it sit for a day or two so that the highly volatile toxins can gradually release into the air. You will notice that the stench will slowly disappear.

Once the mulch has stopped smelling rotten, you can reapply it to your flower beds, making sure that it is not packed too tightly.

Afterward, you simply need to gently rake the mulch, turning it around to introduce more oxygen into the substrate. Watering the mulch regularly also helps to keep oxygen levels high enough that no more anaerobic bacteria can begin to grow again.