Why does mulch smell like manure? Why organic mulch smells bad: reasons

why does mulch smell like manure: Important Helpful reasons Composting FAQ

Every gardener knows that mulch helps keep moisture levels at the right level, as well as prevent the development of weed crops. However, often the mulch emits a sharp and unpleasant odor. You can read more about why mulch has a smell like a pile of manure in this article.

Causes of manure smell in mulch

If you are wondering “why does mulch smell like manure”, then this is due to several reasons. Many people wonder, why does my mulch smell so bad?

It seems to many that there is manure in the composition. However, it is not. You can read more on the main causes of the manure smell in mulch below.

The mulch lay for a long time and became anaerobic

If you start noticing the manure mulch smell, then anaerobic conditions have occurred.

The aroma is quite strong, it is toxic and sour mulch. Often you can notice the smell of rotten eggs, ammonia, and vinegar. Often this is faced by those gardeners who use commercial manure.

Due to mass production, it is stored in the wrong conditions. It is possible that the containers were stacked in large piles, so the air from the mulch was gradually sucked out.

Almost all mulch sold in the markets is packed in airtight bags. This is what provokes anaerobic degradation.

As the mulch begins to decompose under anaerobic conditions, the formation of acetic acid and hydrogen sulfide can be seen.

This is what causes the bad manure smell. If the mulch is decomposed in this way, then the acid values ​​begin to rise.

If normal mulch has a pH of 6, then under anaerobic conditions, the value begins to drop to 2.

Mulch with a high acid content and toxins, including acetic acid and methanol, begins to harm plants very much. Therefore, the harm from it is more than the good.

Mulch decomposes and smells like manure

If you notice that the mulch is beginning to smell strongly of manure, then it is already decomposing.

Often this applies to cases where gardeners use organic compounds. The natural decomposition of mulch is provoked by microbes, including bacteria and fungi. Most often, gardeners suspect actinomycetes.

These bacteria begin to develop precisely in an anaerobic environment. Under the influence of water, heat, humus, and carbon dioxide, organic matter is decomposed.

These microbes can provoke the release of chemicals that have a strong odor. However, it is extremely difficult to meet them.

It is important to understand that actinomycetes are an integral part of the mulching process. They help release nutrients that benefit plants. And the smell of decaying mulch is not as strong as many people think.

Bad smell from rubber mulch

If you’ve stocked up on colored mulch, the odor may be caused by the paint it contains. Most often, the mulch is stained with red oxide, which emits an unpleasant rust smell.

Black mulch is formed as a result of exposure to carbon dyes. But, they do not emit an unpleasant odor.

It is allowed to use old wood, which is treated with copper arsenate chromate. It is a preservative that emits a pungent and unpleasant odor. The black rubber mulch emits a pungent odor that resembles the smell of new sneakers or car tires.

This smell disappears a few days after mulching the area. However, if the weather is hot, then the unpleasant aroma only intensifies.

Therefore, going outside is a torment. In this case, the plants do not receive any benefit.

How should mulch smell?

If you start noticing that the mulch has a bad smell, this is not a good indicator. Even a good mulch has a scent, however, it shouldn’t be off-putting. If you notice sour mulch or toxic mulch with the smell of rot, then something is wrong with your mixture.

The vinegar smell indicates that acetic acid is contained in the composition of the mulch. It only harms plants. The same applies to cases when the mass begins to smell like ammonia.

A good mulch should smell like fresh compost. Often some options have the aroma of sawdust that has been cut down recently.

The smell can determine the quality of the mulch. If the aroma is sharp and unpleasant, then the mulch should not be used. After all, you only harm your plants.

Only mulch that has the smell of wood is beneficial. That is what you need to use for gardening.

Ways to eliminate the smell of mulch

Many people ask, how do you get rid of the smell of manure in the garden? If you’re using black rubber mulch, don’t worry.

The smell from black rubber mulch disappears within a few days after the distribution of the composition of the soil. However, it should not be stored in the open sun, or heated.

To combat organic fertilizers, aeration is required. All methods are in more detail below.

Proper storage

Do not store mulch in bags that have an airtight closure. If this requirement is ignored, anaerobic decomposition occurs.

Poor air circulation only exacerbates the situation. That is why you should use bags that are made of burlap. Alternatively, use open containers.

It is important to periodically fluff the mulch so that it is well-ventilated. This causes air pockets to form. You can lay out a mulch that is not yet in use. After it needs to be covered with a rag or tarp to protect it from rain and weeds.

To fix the covering material, you can use stones or earth. If you store the mulch in bags, you need to make small holes in them. It is best to store mulch in a dry, well-ventilated area. This contributes to a pleasant smell.

Mulch layout for drying

The easiest way to deal with an unpleasant manure smell is to spread the mulch in an open area. It is better to do this in an area that is well-lit by sunlight.

Wind and ultraviolet light block the toxins. Do not forget to periodically ventilate the mulch.

Whipping mulch

To remove the unpleasant odor, you can beat the mulch a little. However, it must first be distributed for convenience. This helps increase aeration, as well as remove the sulfur smell.

If the mulch decomposition is under the influence of oxygen, you notice a pleasant smell.

Whipping should be carried out at intervals of 1 time per month. This is very important if the mulch contains a lot of organic matter.

How to use mulch?

Before applying the mulch, you need to make a few holes in the soil. The layer of mulch should be 2-4 inches.

If the thickness is greater, the layer collapse under its weight. In this case, it is difficult for oxygen to penetrate deep into the soil.

Do not use mulch that emits an unpleasant odor. Otherwise, the plants deteriorate and may die.

Unfavorable symptoms in plants

You can find out that the mulch was of poor quality by the condition of the plants. The main symptoms include:

  • the yellowness of leaves;
  • growth retardation and loss of plant viability;
  • burnt leaves;
  • death of a bush.

The best natural mulch

The choice of mulch depends on the plants being grown as well as the landscaping. There is organic mulch and inorganic mulch.

The organic mulch is appropriate for experienced gardeners. Organic mulches are safer.

Some microorganisms that are in the soil break down the components into nutrients. This positively affects the development of plants.

There are wide varieties of natural mulch.

Chips from cedar bark

They are small in size and low cost. They have a long decay time.

However, they can spoil landscape design, because they are not fixed on the soil. This is the best option for indoor plants and greenhouses.

You can find different varieties of chips. The larger the size, the longer the mulch lasts.

Pine leaves or straw

Pine leaves and bark also make great mulches. The use of dry pine needles is allowed. Such options are distinguished by an attractive appearance, as well as a long service life.

The needles are considered abrasive, so they do not wash away by rain. Pine acidic mulch is a great option for plants that love acidic soil.

Compost as natural mulch

Compost, in appearance, resembles soil, however, it has a darker shade. They can be used to mulch plants to make them stand out.

Differs in high speed of decomposition and therefore quickly improves the structure of the soil. Composting as mulch has many benefits.

This is an inexpensive option that can be found for free in a nearby park. You can make compost at home using leaves, chopped stems, and grass cuttings.

Compost retains soil moisture and nourishes it with nutrients. Compost can block diseases, as well as prevent the appearance of pests.

Cut grass mulch

This option is very environmentally friendly and can be easily recycled.

Mowed grass keeps the right moisture in the soil and also prevents weeds. In this case, the soil is saturated with potassium and nitrogen.

Mowed grass is not only cheap but also helps to repel pests. However, it must be laid in a layer, the thickness of which is 1-2 inches.

At first, it is best to lay only 1 inch, gradually increasing the thickness.

The grass cuttings can only be used in a dry state. Wet grass compacts, preventing the soil from breathing and absorbing moisture.

Small plates of pine bark

Wood chips from pine bark work well as mulch. They are a bit like cedar bark chips, however, they remain motionless, so they last longer.

Pine bark is darker, so it is often used in landscape design. By keeping the mulch in place, the soil retains moisture longer.

Given that such a mulch is considered organic, it saturates the plants with nutrients.

Therefore, you do not have to fertilize often.

It also helps prevent diseases and pests. It is believed that pine bark mini nuggets help protect plants from cold and hot weather.

Cypress mulch

Visually, it resembles pine straw. However, it has a low cost. When organic matter decomposes, the soil is saturated.

Cypress mulch is the best solution if you need to prevent the development of weeds on the site.

However, try not to abuse such mulch. Indeed, because of this, entire groves of trees are being destroyed.

Safe mulch options

There were listed natural mulches above that do not pose a danger to the soil and plants. They are inexpensive and fall into the category of organic mulch. However, to preserve nature, try to abandon the cypress mulch.

Try to use mulch sparingly. The optimum layer thickness is 2-4 inches. If the thickness is greater, soil moisture and air can not penetrate, so the plants suffer.

Don’t use toxic mulch. If it emits an unpleasant odor, you must first get rid of it using the methods that were described earlier.

How long does it take for mulch to stop smelling?

On average, an unpleasant odor persists for 3-14 days. Given that the mulch dries and airs out, you won’t have to wait months.

To speed up the weathering process, distribute the mulch in small layers. If you store it in large piles, the unpleasant aroma only intensifies.

Do not use damp mulch, as it retains the smell much longer. It is better to spread the mulch on a tarp before use, dry it and ventilate it.


When it comes to the use of mulch and its unpleasant smell, many questions arise. The answers to them are below.

Can mulch cause nausea?

Yes, if it contains sulfur, acetic acid, and methanol. These are toxic substances that often provoke nausea and illness.

Should old mulch be removed?

If the mulch has been on the site for more than a year, it should be removed.

This allows you to adjust the airing of the soil, which eliminates root rot, which provokes the death of the plant.

What mulch smells best?

If you’re looking for good-smelling mulch, try using pieces of pine bark or pine needles.

Why does my yard smell like manure?

This is because the grass began to compost on its own. Grass that rots and decays smells like manure.

Does mulch have manure?

Mulch contains no manure. It is made from plant materials that decompose and give off the manure smell.


As you can see, manure mulch smells bad for several reasons. However, you should not be upset. You can dry it and air it out, or use a different mulch.

Read also: How to store potting soil indoors, in a protective container and big thin plastic bags?

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