Many a gardener often become confused when it comes to the difference between compost and mulch. After all, they are both organic materials, and they are both beneficial to the soil, so what’s the difference?
- Strictly speaking, mulch is any material that covers the soil. It could be made of organic materials like compost, leaves, grass clippings, or straw; or it could be made out of inorganic materials like gravel, pebbles, and rubber. These materials serve to preserve soil moisture, suppress weeds, and regulate temperature amongst other benefits.
- Compost is a mixture of materials such as decaying plant and animal matter, This includes food scraps, grass clippings, wood chips, and leaves. These materials are usually added to the soil after a period of decomposition in order to make the nutrients easily available. As they decompose, they add valuable nutrients to the soil to promote soil health and help plants grow.
The key visual difference is that mulch covers the soil whilst compost is worked into the soil.
| Mulch | Compost | |
|---|---|---|
| Definition | Any material that covers soil. | A mixture of decaying plant and animal matter added to the soil. |
| Types | Organic (leaves, grass clippings, straw, wood chips, pine needles, shredded bark) and inorganic (rocks, pebbles, rubber mulch, landscape fabrics). | Primarily organic materials like food waste, straw, wood chips, leaves, and manure. |
| Benefits | Retains moisture, suppresses weeds, regulates temperature, and adds nutrients as it decomposes. | Adds organic matter, improves structure and aeration, provides nutrients, retains moisture, promotes earthworm populations, and acts as an insulator. |
| Disadvantages | Can become compacted, reducing water infiltration; may attract pests; may temporarily deplete nitrogen in the soil. | Can take time to produce; needs to be turned regularly; can attract pests if not properly maintained; quality varies depending on materials used. |
| Application | Applied directly on top of the soil. | Worked into the soil. |
| Process | Mulching involves applying a layer of mulch material to your garden. Mulch can be bought from stores or made yourself from fallen leaves, twigs, and other debris. | Composting involves collecting organic materials, combining them in a compost bin or pile, turning and mixing regularly, monitoring moisture levels, and waiting for the compost to break down. |
What Is Mulch & Mulching?
Mulch is typically organic material that promotes the health of your soil and plants. When applied correctly, mulch has several benefits:
- Retains moisture in the soil. This is great for keeping plants hydrated, especially during hot summer days.
- Reduces weed growth by blocking light from weeds and preventing them from germinating;
- Moderates temperature of your soil to keep roots cool on warm days and warm on cold days;
- Adds nutrients as it decomposes, which helps improve the soil structure;
- Aesthetically pleasing. You can choose a mulch that matches your landscape and provide contrast to your plants.
There are many types of mulch that fall under two categories – organic and inorganic.
Organic mulch refers to mulches that are organic in nature and decompose over a period of time.
Organic mulch includes:
- Leaves
- Grass clippings
- Straw
- Wood chips
- Pine needles
- Shredded bark
Inorganic mulches are not organic and take an extremely long time to break down.
Inorganic mulch includes:
- Rocks and pebbles
- Rubber mulch
- Landscape fabrics
Whilst both organic and inorganic mulches provide all the benefits of mulch, inorganic mulch does not contain nutrients and will not add this to the soil.
Mulching is the term used for the process of adding a layer of mulch material to your garden. It is applied directly on top of the soil.
There is no exact time as to when you should mulch. It can depend on where you live and what climate you experience. Generally speaking, many gardeners will choose to mulch after the soil warms up. This is around the middle to late Spring.
It’s also great to mulch just after a light rainfall, as this will help lock in the moisture. Avoid mulching before intense rain or wind as these elements may disturb the mulch before it has had time to settle.
When applying mulch you should adhere to a thickness that is recommended by the specific mulch you are using. This is usually around 2 – 6 inches. Make sure not to pile mulch near plants or trees as this can suffocate them and cause root rot.
What Is Compost & Composting?
Compost is a material that is added to the soil to enrich it with nutrients and promote healthy plant growth. It is made up of organic materials like food waste, straw, wood chips, leaves, grass clippings, and manure.
Compost has several benefits for your garden:
- Adds organic matter to your soil, which helps improve its structure and aeration.
- Provides extra nutrients to the soil for plants to absorb such as nitrogen, phosphorous, and potassium.
- Helps retain moisture in the soil.
- Promotes earthworm populations which help with soil health.
- Acts as an insulator to reduce soil temperature swings.
Compost works great as a soil fertilizer and amendment.
Composting is the process of combining these organic materials together so they can be applied to the soil in the form of compost. Here are the general steps involved in composting:
- Collect organic materials. This can be from the garden, kitchen scraps, or even leaves and grass clippings. Chop or shred materials into small pieces so they can break down faster.
- Combine the materials in a compost bin or pile.
- Turn and mix the material regularly to add oxygen. Oxygen will speed up the breakdown process as this will feed the beneficial bacteria and other microorganisms in the compost.
- Monitor moisture level and adjust as necessary. Moisture should be kept at a level where it is moist enough for the compost to be squeezed into clumps without dripping wet. An adequate level of moisture allows the microbes to thrive and effectively decompose the compost material.
- Wait for the compost to break down – this could take anywhere from two to six months or more, depending on conditions. This also depends on the type of material involved.
Tip: In order for composting to work the most efficiently, note the green and brown ratio. This refers to the ratio of green materials (such as grass clippings and kitchen scraps) which are high in nitrogen, and brown materials (such as leaves and straw) which are high in carbon. Aim for a 3:1 or 4:1 ratio of carbon to nitrogen when adding materials.
The final compost will look like a dark, crumbly material with an earthy smell.
The Key Differences Between Mulch & Compost
It’s apparent now that compost and mulch are similar but two different things.
Mulch is applied on top of the soil while compost is worked into it.
Another thing worth noting is the availability of nutrients. Mulch is applied to the soil in a mostly non-decomposed state. In other words, it will take a lot longer for nutrients to work their way into the soil and into the root of the plants. Also, as mulch decomposes it will tie up the nitrogen in the soil for a period of time which can strain your plants and lead to chlorosis for delicate plants.
Compost, on the other hand, will immediately provide the beneficial bacteria and nutrients necessary for healthier plants.
Unlike mulch, compost is mostly made up of organic materials. Meanwhile, mulch can be bought in a completely inorganic form like that you would see with rubber or rock mulch.
Inorganic mulch will not provide any nutrients to your plants, so it’s worth considering using compost to make up for this lack.
Can You Use Compost As Mulch?
Given that mulch and compost can be seen as quite similar, one would think that compost can be used as mulch. As it turns out, you can use compost as mulch if you prefer.
You can apply the compost on top of the soil as you would mulch. The main advantage of this is the soil will get the nutrients a lot quicker from the compost and plants won’t be nitrogen sapped since the majority of the compost would have already decomposed.
The biggest drawback to using compost as mulch is its weed suppression abilities. Simply put, weeds will have a lot easier time sprouting through the soil because compost won’t provide as much protection as regular mulch.
If you want to use compost as a mulch, it’s best to add some mulch materials through it like wood chips. That way, you can use these wood chips to smother weeds, whilst allowing the compost to continue enriching the soil.