Compost VS Topsoil – What’s the Difference?

Quality and healthy garden soil is the key to successful gardening. When choosing the materials required for your landscape or garden, you may have questions regarding topsoil and compost, such as their differences, and when to use which to grow lush grass or beautiful flowers.

Topsoil and compost are almost the same in appearance and play vital roles in potting mix for healthy gardens. Nevertheless, although you may need to use both, they serve different purposes.

This article helps you understand the differences between compost and topsoil and where to use them best to realize your desired gardening outcome.

What Is Topsoil?

Topsoil is the upper, outermost layer of soil where the soil biological activities occur most. It consists of mineral molecules, organic material, water, and air

Organic matter amounts vary on different soils, and the more organic matter present in a soil, the lesser the strength of the soil structure. 

For naturally existing soil, the screened topsoil is the layer with the most organic matter and microorganisms. This explains why although topsoil contains a considerable amount of minerals, it’s not sufficient for sustaining your plants until maturity.

What Is Compost?

Compost is decomposing organic matter. The nutrients formed in a compost pile act as a natural fertilizer for plants and flower beds.

Composted manure, grass clippings, and organic material improves soil structure, minimizing compaction and enhancing water retention while improving drainage.

Humus is the best compost, and it consists of organic matter broken down into tiny particles.

Difference Between Topsoil and Compost

Both topsoil and compost are formed through the decomposition of organic matter, are rich in nutrients, and have a high concentration of beneficial microorganisms. However, they’re not the same.

How do they differ?

While both have a lot in common, the difference between premium topsoil and compost is in their application. You’ll often use compost as an organic enhancement or soil amendment. That means letting organic materials decompose to a level where they have a fine texture.

In most cases, you use compost as potting soil. You’ll also apply it as an amendment to native soil, clay soil, sandy soil, or loam soil as a top-layer fertilizer to your garden.

On the other hand, topsoil is better when used as a landscape filler or for expanding soil. In fact, what you get after ordering topsoil in large quantities is dirt mixed with some organic matter.

Additionally, depending on your needs, you can use a combination of both bagged compost and topsoil in your garden. For instance, you can combine topsoil and compost and spread a layer of the mixture on your current soil to prepare it for growing plants. Combined with peat moss and the proper mulch, it can even block weed seeds from sprouting.

Is Topsoil Better Than Compost?

Compost contains more nutrients than topsoil. But this doesn’t mean topsoil has no advantages. On the contrary, topsoil is far better than compost in terms of holding moisture and retaining the soil structure.

The two work hand in hand to create productive and healthy soil for our gardens and lawns. Each has its role to play in ensuring a healthy soil ecosystem. Therefore, none is better than the other.

Can You Use Compost as Topsoil?

Compost doesn’t turn into soil. Therefore, you can’t use it as soil.

If you need potting soil or topsoil for your lawn or garden project, you can’t just replace the soil with compost. Instead, you’ll use compost to improve the topsoil.

Although compost is rich in nutrients, and ensuring the plants are fed fully with the nutrients they need is essential, too much of it isn’t good.

If you use compost with no soil, your plants may experience fertilizer or nutrient burn, making plants unhealthy.

With excessive nutrients in your garden, plants may not be able to absorb these nutrients or water. In addition, too much nutrients can alter the pH of the growing medium. In such a medium, plants may not thrive.

Therefore, the best thing to do is add compost to your topsoil and mix them rather than grow plants directly on pure compost. 

Do You Need Topsoil and Compost?

Topsoil and compost work together to create a better and healthier growing medium for plants. Therefore, first you need to mix compost with your native topsoil, and then after that plant on this mixture.

The question is, how do you mix the two?

Add two to three inches of compost to your topsoil, then work it into a depth of approximately six inches. However, if you want to make a raised bed, mix compost, topsoil, and sharp sand in equal measures. The reason why we add sand is to improve drainage.

Are you planting in pots? In this case, mix four inches of topsoil with compost. Alternatively, top-dress your container with compost.

Both topsoil and compost are necessary for creating productive soil, and you’ll often need to use them both.

Is Multipurpose Compost the Same as Topsoil?

Traditionally, multi purpose compost is a blend of peat moss and several other materials such as fertilizer, lime, bark and green compost. It’s all about creating a nutrient level and pH that favors the growth of different plant types.   

You can use multipurpose compost to fill containers, sow seeds, and repot plants.

So no, multipurpose compost is not the same as topsoil. While topsoil adds bulk, multipurpose compost increases quality. Like standard compost and topsoil, the two have different applications, and compost can never be soil.

Does Compost Turn Into Soil?

You see, soil is not a single thing as most of us think. It’s complex, consisting of a mixture of various substances.

Have you ever tried looking at soil over a microscope? If you do, you’ll see some silt, clay, and sand together with water, microorganisms, minerals, and organic matter. Soil is a combination of all these components.

In addition, soil contains gases such as nitrogen, oxygen, and carbon dioxide in significant amounts. These gases are also vital for the proper development of plants.

What happens when compost decomposes is that it turns into a substance known as humus. Humus has a fine texture and is what forms the organic matter part of the soil.

Although organic matter ranges between one to three per cent of the total soil, its composition keeps changing. That’s because plants utilize some of it for growth, and when they die, they break down and become part of it.

So, does compost turn into soil? As mentioned, the soil is a combination of several components of which compost is a part.  But in and of itself, it doesn’t turn into soil.

Take Away

Now you understand better the difference between topsoil and compost. Both are used to achieve diverse goals. However, for long-term results in your lawn or garden, you can use a combination of them.  

Always remember topsoil is an excellent base for your already nutrient-rich garden. On the other hand, whenever your plants need extra nutrients, nutrient-rich compost is an ideal solution.  


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