Compost vs Mulch – What is the Difference Between Compost and Mulch?

Confused about the differences between compost and mulch? Both are often mentioned in gardening guides, but they each serve very different purposes. Here’s everything you need to know about compost vs mulch.

Compost vs Mulch - What is the Difference Between Compost and Mulch?

Mulch vs Compost

While compost can be used as a mulch, other mulches can’t be used instead of compost, which is why comparing the two can seem tricky at first. Let’s break it all down…

Compost vs Mulch - What is the Difference Between Compost and Mulch?

What is Compost?

Compost is decomposed organic material. It looks and feels just like soil, and can be made up of a variety of different organic matters, such as:

  • Animal manure
  • Kitchen scraps
  • Yard waste and lawn clippings
  • Paper and cardboard
  • Garden soil

These items are gathered together, either in a heap or in a compost bin. With the addition of water and time, the process of aerobic biodegradation causes all of those materials to break down, resulting in a nutrient-rich compost.

Compost vs Mulch - What is the Difference Between Compost and Mulch?

What is Compost Used For?

Compost can be used in a few different ways:

  • Mixed into garden soil to improve soil aeration and structure while adding nutrients to the soil.
  • In raised beds and containers for growing plants.
  • As a mulch.

What is Mulch?

Mulches can be both organic and inorganic.

They are used as a top-dressing, spread over the surface of soil around plants and trees.

There are several different types of mulch out there, but some of the most popular are:

Inorganic materials, such as plastic sheets, recycled rubber, or gravel, can be used as a mulch too. However, the term “mulch” usually refers to organic materials that break down over time.

Compost vs Mulch - What is the Difference Between Compost and Mulch?

What is Mulch Used For?

Spreading a mulch over the surface of your soil has a number of benefits:

Since most mulches are organic in nature, they slowly decompose over time. As this happens, nutrients are added into the soil, not only improving its fertility but also its structure.

Compost vs Mulch: The Main Differences Summarized

If you’re still feeling a little confused, here are the main differences between compost and mulch:

  • A mulch is laid over the top of soil, whereas compost is mixed in, or used on its own instead of soil.
  • Compost is always made up of decomposed organic materials. A mulch is often made up of organic materials too, but these are usually in their whole form rather than being decomposed.
  • Compost is full of nutrients, in a form that’s readily available to plants. An organic mulch will only release its nutrients once it starts to break down.

Take your lawn clippings as an example. These can be spread over your garden beds and around the base of your plants in their whole form. This mulch will prevent weeds from popping up, while keeping your plants moist and at a consistent temperature.

Alternatively, your lawn clippings could also be added to a compost heap, along with other organic materials. Once the whole heap breaks down, the compost can then either be mixed into your garden soil or used in pots and containers.

Combining Compost and Mulch

As you can see, compost and mulch work in 2 very different ways.

Ideally, you should be using both in your garden for maximum benefits.

While compost will work its magic in the deeper layers of your soil, the mulch will protect and nourish from above, giving your plants a double dose of goodness.

This video is a primer to get you started with the language of compost and mulch:

Using Compost as Mulch

Compost vs Mulch - What is the Difference Between Compost and Mulch?

Even though compost differs from most other mulches because it contains organic materials that have already broken down, it still makes a fantastic mulch.

It provides all of the same benefits as other types of mulches, but with the added bonus of being even richer in nutrients, all of which gets sent straight over to your plants.

Each time it rains or you water your compost mulch, those nutrients get pushed deeper and deeper into the soil, which really enriches it and boosts its health.

How to Use Compost as Mulch

Using compost as mulch is easy. All you need to do is spread a layer of compost over the surface of your soil around your plants. Extend this outwards by about a couple of feet.

As with all mulches, the thickness of your compost layer is important. Mulches need to be between three and four inches thick in order to prevent the sunlight from penetrating through and activating all of those weed seeds.

Don’t be tempted to pile it on too thickly, however…

A mulch that is too thick will become hydrophobic. This means that it will prevent water from reaching the soil beneath. A too-thick mulch could also harbor a number of diseases and pathogens, causing more harm than good to your plants in the end.

Ideally, mulch your plants with compost twice a year; once in the spring and once in the fall. This will help to ensure good water retention during the hot summer months, while also protecting your plants from the cold in the winter.

Unlike many other mulches, a compost mulch does not need to be removed each time you re-mulch. Instead, your next layer of compost mulch can simply be spread over the top.

A Double-Layered Mulch

If you don’t have enough compost for a four-inch layer of mulch, you can always combine your compost with another mulching material.

To do this, spread your compost mulch around your plants in an even layer. Then, top this with another mulch, whether this may be shredded leaves, grass clippings, or anything else.

For further information, let’s watch this video:

Conclusion

Many gardeners often compare compost vs mulch because they want to know which one is best for their garden.

The answer is both – one works from below while the other works from above, and combining the two is what will bring you the biggest transformations when it comes to the health of both your garden soil and your plants.

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Jill Sandy

Jill Sandy

Jill is a sustainable focus gardener. She loves decorating her home backyard with beautiful landscape design and creative garden care techniques she develops herself. You can reach her at jill.sandy@constantdelights.com

Chanh Ho (MD, MPH)

Chanh Ho (MD, MPH)

Chanh is our Head of Medical Review. He is a research physician at Oxford University Clinical Research Unit. After accomplishing the program of level 1 sub-specialty in Pediatrics, he was awarded the Chevening Scholarship for his Master’s degree of Public Health in the University of Edinburgh in 2019

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