On the surface, compost mulch may seem like a confusing term. What is it? Does it have some kind of special formulation? Is it better or worse than standard mulch you can buy at the garden store, or are they basically the same thing?

Most of the confusion comes from the fact that people often use the words “compost” and “mulch” interchangeably. The combined name “compost mulch” only muddies the waters further. However, each term actually refers to a very specific (and very different) concept. 

Ready to get some clarity? In this article, we’ll break down the definition of each term and provide helpful examples. You’ll also learn about the pros and cons of compost mulch as well as proper usage tips.

What Is Compost?

When living organic matter dies and decomposes, it returns to a simple state in which the basic minerals and nutrients are available to the surrounding environment. 

This is compost in a nutshell. Often referred to as “black gold” by gardeners, compost adds vital nutrients to your soil. 

Examples of Compostable Materials​

You can make compost from almost any biological material. This list is just a fraction of good composting ingredients.

• Eggshells
• Tea Bags (but take out the staples!)
• Vegetable peelings and scraps
• Fruit cores and skins
• Coffee grounds
• Paperboard egg cartons
• Shredded leaves
• Grass clippings
• Cow manure

Here’s a couple of photos of the kinds of things I add to my compost bin: 

What Is Standard Mulch?

Mulch is any material you spread over the top of your soil. Gardeners have a few main objectives in mind when laying down a layer of mulch. 

• Retain soil moisture
• Reduce weeds
• Prevent soil erosion
• Moderate soil temperature

Many different materials qualify as mulch. These materials fall into two main categories: organic and inorganic. 

Organic Mulch​

Organic mulch is made up of elements found in nature that will break down over time. Here are just a few natural materials that you could use as mulch.

• Chopped or shredded leaves
• Grass cuttings
• Pine straw
• Wood chips or shavings
• Hay or straw

Inorganic Mulch​

The term inorganic mulch refers to substances and materials that were never alive and won’t decompose to a significant degree. These are a few common inorganic mulch materials. 

• Tire shreds
• Garden fabric
• Dark plastic sheeting
• Pebbles or crushed rock

What Is Compost Mulch?

The answer to this question may be a bit underwhelming. Compost mulch is simply using compost as mulch.

Compost has several unique garden benefits to offer, and using it as a mulch can be a great long-term strategy. 

Benefits of Compost as Mulch

Compost is a nutrient powerhouse, so any way you can add it to your garden is a win. While most people work compost into the soil, applying it as a top-layer mulch brings multiple advantages.

Introduces Beneficial Microbes

Friendly microbes break down organic material to create compost. When you use compost as mulch, you’re also adding these helpful microbes to your garden soil. 

Enhances Soil Texture Long-Term

Sandy, compacted or clay soil is hard to work with, both for plant roots and the human gardener.

Also, in areas that need re-planting every year (think vegetable gardens), repeated tilling can lead to soil compaction and degradation over time. 

Compost has a light, fluffy texture that helps increase drainage, promote better aeration and improve your soil’s overall structure over time. 

This can lead to healthier overall soil with long-term growing conditions and maybe even fewer passes with the tiller. 

No Nitrogen Depletion

Most wood-based mulches are extremely high in carbon and low in nitrogen. As a result, these mulch materials can leach nitrogen from your soil and cause mineral deficiencies in your plants.

Thanks to an abundance of biological material, compost is a rich source of nitrogen.

Reduced Risk of Spreading Fungi or Diseases

Some mulch materials, like wood chips, can harbor plant diseases and mold spores. Using contaminated mulch can spread these harmful microbes and infect healthy plants.

During the composting process, helpful bacteria break down and neutralize most of these hazards

Drawbacks of Compost as Mulch

Using compost as mulch offers several outstanding advantages, but there are a couple of concerns to keep in mind. The good news is that there are simple solutions available for most problems.

Cost

High-quality compost can be very expensive. Depending on the size of your garden, you may be looking at a significant investment.

Solution: Make your own compost.

Home composting not only produces a high-quality soil amendment, but it’s also perfect for recycling garden and kitchen refuse.

However, compost takes several months to a couple of years to fully decompose, so you’ll have to look at other options in the meantime.

Additionally, if you have a large garden, you’ll need a large amount of compost. Depending on your location and resources, you may not be able to produce the amount of compost needed to mulch your entire garden.

Greater Potential for Pests

Mulching your plants with compost can have two effects:

1. Increases plant nutrient density
2. May cause the plant to produce fewer protective chemicals

As a result, some plants may be more attractive to pests and have a decreased ability to defend themselves.

Solution: Place compost strategically.

If you have plants that are especially prone to pest infestations, incorporate a less insect-friendly material. Shredded bark or wood chips can be a good choice. Mix the shredded bark with your compost in about a 3:1 ratio.

Using Compost Mulch

You don’t need any specialized tools or skills to use compost as mulch. All you need is a shovel, a garden rake and some elbow grease.

Here are some tips for applying compost mulch in vegetable gardens or flower beds:

Depth

The general depth recommendation for mulch of any type is about 2 to 4 inches. Laying a thick layer serves several purposes:

• Block sunlight from reaching any weeds that may be lurking under the soil surface
• Conserve precious moisture at the roots
• Protect soil from drastic temperature fluctuations

Width

Apply the compost mulch in the area that extends from your plants stems to about 12 inches away. For plants that have wide lateral roots systems, this technique can be particularly beneficial.

To conserve costs, consider using a different material for mulching garden pathways. Unless, of course, you have a large compost pile of your own that you want to use up!

Frequency

Compost breaks down and mixes with the soil at a faster rate than most other mulch materials. Hence, you’ll need to apply a fresh layer of compost at least a couple of times per growing season.

But that’s a good thing! As water from rain or your hose falls onto the compost, particles get washed deeper into your soil. As a result, your plants have more nutrients available at the root level.

Final Thoughts

In summary, compost mulch doesn’t have to be a confusing term. After all, it simply refers to the process of using compost as a protective garden mulch. 

Options abound when it comes to both organic and inorganic materials for mulch. However, using compost as mulch can be a great choice for your garden’s short-term performance and long-term health.