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Does Mulch Turn Into Soil? (And How Long Does It Take to Decompose?)

Does Mulch Turn Into Soil? (And How Long Does It Take to Decompose?)

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Many gardeners swear by mulch because it greatly improves the conditions of the soil. If you haven’t added mulch to your garden in a while, you might want to seriously consider doing so.

Mulch offers a plethora of benefits that you don’t get with other materials, and it’s an excellent option for people who want to maintain the right conditions in the soil.

Before we go further, it’s important to clear up the basics. Mulch is simply any material, either organic or inorganic, that can be placed on top of the soil. Mulch can be added to any garden and offers multiple benefits.

Apart from the decorative value that it offers, mulch also provides considerable benefits to the plants.

For starters, mulch reduces the amount of water that evaporates from the soil. This is important, because in areas where rainfall is relatively low and the water table falls all the way down, the quality of the crops could be seriously affected. To prevent this from happening, you need to make sure that you add a bit of mulch to the soil.

Moreover, the mulch creates a layer of protection against the harmful rays of the sun, and keeps the soil moist and cool for a longer period of time.

During the cold winter months, the mulch lessens the effects of the frost as well as it prevents the heavily fluctuating temperatures and reduces the impact on the roots.

Increasing the amount of organic matter in the soil can also improve the level of moisture and the nutrient holding capacity of the soil itself. It also improves drainage and the overall structure of the soil.

Moreover, the addition of mulch in the soil also promotes growth of soil organisms that can be beneficial to the soil itself.

Now, a common question that many people have is about what happens to the soil itself. What happens to all the mulch that has been laid down? For instance, what about wood chippings and other kinds of mulch that is used?

Well, the answer is that with the passage of time, this mulch decomposes into soil itself.

However, the answer is not as straightforward as you might think. Mulch does not decompose right away, and there are several factors that need to be taken into account, such as the conditions, the climate, and of course, the kind of mulch that you have used.

If the mulch was treated beforehand, it’s going to take much longer to decompose as opposed to untreated mulch.

Why Is This So Important?

You might not realize this, but this information is actually quite important for a variety of reasons. Certain kinds of mulch such as bark mulch, wood chips, and shredded leaves, tend to consume the nitrogen from within the soil when they begin to decompose.

Basically, the micro-organisms tend to decompose, and eventually they start to require more nitrogen.

That is one of the main reasons why wood chips and bark mulch (the two most popular types of mulches) tend to consume a great deal of nitrogen when they decompose.

However, if they consume an excessive amount of nitrogen from the soil, it could stunt the growth of the plants. Moreover, it may prevent essential nutrients from reaching the soil.

To ensure that the nitrogen in the soil isn’t affected, the best thing you can do is add a bit of nitrogen or ammonium sulphate to the soil. This will help improve the speed of decomposition and will also improve the vegetation.

But, you need to make sure that you do not add too much of it. Excessive application of nitrogen or ammonium to the garden could also end up poisoning the plants.

How Long Does It Take for Mulch to Decompose?

Decomposed Mulch

Now, a common question that many people have in mind is about how long it takes for mulch to decompose. Well, in standard weather conditions with the proper amount of sun, the mulch will take around a year to start breaking down.

Within a span of three years, the mulch will break down completely, and this will provide fantastic nutrients to the soil.

On the other hand, treated wood chips tend to take longer. For instance, treated wood chips usually take around four years to break down completely. Usually, the mulch begins to decompose after a couple of years.

There are a few factors that directly affect the decomposition of the mulch into the soil. Let’s talk about them.

Moisture in the Soil

Soil Moisture Meter

The more moisture there is in the soil, the quicker the soil is going to decompose. Moisture promotes the effective breakdown of nutrients and the soil clears out much quicker, so if you want to speed up the decomposition process, you need to make sure that you add more moisture in the soil.


If the temperature of the soil is warm, the mulch will decompose much quicker. Warmth in the soil plays an important role, and it’s one of the main reasons why mulch is added (to maintain the temperature).

Adding mulch can improve the temperature and keep it from becoming really hot. As the temperature remains heated, the mulch has to work harder, and that is why it decomposes quicker.

We have already talked about how treated or untreated mulch affects the decomposition, so you will want to take that into account as well. Treated mulch slows the decomposition process considerably.

On top of that, additives to the mulch can also impact the decomposition process; nitrogen and ammonium sulphate speed up the decomposition process.

These are just a few things that you should know about how mulch decomposes in the soil. You also need to understand that the temperature conditions in your area also play a role. If the temperature conditions increase, the mulch will decompose quicker.

So, it is easy to say that while mulch decomposes into the soil, it’s much harder to put an exact timeframe on how quickly the mulch is going to decompose into the soil.


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Tuesday 13th of April 2021

Thank you, very informative! I’ve always wondered why people said their mulch breaks down by the following year, it never does for me. Now I realize! I live in Southern California and I have temperate weather year round with really high heat triple digit in the summer, but it’s very very dry here with low humidity. Even with sprinklers, my soil is bone dry within a few days, which is why I lay mulch, to keep it moist a little longer and cool. My mulch fades but it takes a good 2-3 years for it to break down. Also a good tip about the nitrogen. Thank you so much. I’ve clicked on your blog from Pinterest a few times now. I really like how in you’ve honed in on answering some of the smaller but actually pretty important questions people have.