What is the difference between garden soil and topsoil?


Is garden soil the same as topsoil, or is topsoil what is put on top of a garden – added in? Below we look to demystify the topsoil saga and advise you on making that top layer productive.

Topsoil or garden soil – it is a matter of semantics. They are the same and are referenced from the original Greek word for topsoil, epipedon. Epipedon is the surface layer where the rock is mostly broken down by the elements

The earth’s crust is layered, and the upper layer is layered even further. This article gives an overview of both the big picture, interest’s sake, and what gardeners have available as canvasses for their creative and productive genius – the topsoil.

What is topsoil, and how does it differ from garden soil?

Topsoil is described to be made of carbon and nitrogen, as well as microbes and insects alike. They are usually found at a depth of two to eight inches of soil. Their composition also depends on factors such as their geographic region, human activity as well as climate.

Often, the darker the topsoil is, the stronger its earthy smell, the richer it is in nutrients.

Fertile topsoil would contain good nutrients like potassium, phosphorus, and iron. Rich topsoil can absorb more water. The greater nutrients and water availability allow topsoil to be more productive in terms of plant growth. The greatest risk to topsoil is erosion.

With this clarification, we would also like to introduce you to an article we made on the difference between potting soil, garden soil, and topsoil. It further clarifies the differences, similarities as well as tips on the usage of these.

Local Soil Categories

According to the United States Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS), your garden has one of twelve potential garden soil types. The area has distinct regions, each with different vegetation, water volumes, and climates. The interaction between these three variables ( water, plants, and climate) has created twelve categories of organic soil types over thousands of years.

However, whatever you are gardening on can be adjusted by adding manure, compost, earthworms, and fertilizers – if you know what you have. For this, it is advisable to make use of soil testing facilities which will measure:

Factors to checkTheir specifications
Soil textureClay-dominated soil, or sandy loam?
Soil pHHow acidic, neutral, or alkaline is your soil?
Soil NutrientsDoes it contain phosphate, potassium, calcium, magnesium, nitrogen?
Soil Organic MatterHow much is organics versus mineral particles?
Soil Heavy MetalsIs the soil contaminated with industrial metals such as lead and arsenic?

Organic and Mineral Soil

The earth’s upper crust has two distinct layers – organic soil on top and mineral soil below. What differentiates the two is the amount of carbon matter in each. By definition, organic soil has more than 20% carbon matter in its composition due to decomposed plants over the year.

Mineral soil, by definition, is water-saturated for less than 30 days per annum in normal years and contains, other than potential roots, 20 percent (by weight) organic carbon.

In this article we will only be looking at organic soil as that is the primary domain of the gardener.

Organic Soil Layers (Epipedon)

Each of the twelve organic soil types defined in the USDA Soil Taxonomy has its unique soil profile based on factors like color, texture, structure, thickness, and chemical composition. The soil comprises a series of layers stacked on top (source) which can also be called horizons, are represented by letters O, A, B, C, and R.

The O-Horizon

O is the horizon for organic material. This upper layer mainly comprises organic materials and decomposed materials ( dried leaves, grasses, dead leaves, twigs, surface organisms, the former). This horizon of soil is often black-brown or deep brown in color, mainly because of organic content.

The A-Horizon or Topsoil

Also known as the humus layer, this layer is rich in organic material and can hold both moisture and gasses – mainly oxygen, nitrogen, and carbon dioxide.

The topsoil is the layer where seed germination occurs, and new roots are produced, growing into a new plant.

It contains microorganisms such as earthworms that release much-needed nitrogen, fungi, and bacteria.

The B-Horizon or Subsoil

In this subsurface horizon, present just below the topsoil and above the bedrock, there is limited humus, soluble minerals, and organic matter. Dependent on where you are in the US, this horizon is approximately 12 to 18-inches below the surface.

This horizon is comparatively harder and more compact than topsoil. There may be some deposits of certain minerals and metal salts, such as iron oxide.

During the instances that soil gets ploughed too deeply, the soil of horizon-A and horizon-B often get mixed.

The C-Horizon or Saprolite

A layer below B-horizon devoid of any organic matter and made up of broken bedrock. This layer is also known as saprolite and is more prevalent in Oregon and Wisconsin in the United States. It may be important to note that the geological material in this zone is cemented.

The R-Horizon

R for Rocks. It is a compacted and cemented layer. Several types of rocks, such as granite, basalt, and limestone, are found here.

Adding Carbon Material and how to put it in garden soil or topsoil

It could be a topic for philosophical contemplation, but adding matter which had a previous life improves the life-giving force of soil. Soil that is rich in nutrients and carbon matter is better able to sustain growth for fresh plants.

It is better to plant a $1.00 tree in a $10.00 hole than the other way around. Preparing your soil through the addition of compost, manure, earthworms, and fertilizer adjustments makes a significant difference to the outcomes of your planting.

Compost is life in the garden. It feeds the microbial and fungal life, which in turn feeds your plants. Purchased compost usually is full of organic matter but devoid of life due to the high temperatures that it gets to. Home-made is so much better.

The video below will show you how to make compost at home that is perfect every time

Add Compost to your garden soil or topsoil

Composting can be made at home and maybe super easy to make. Some several tips and tricks can be followed with regards to putting them into our garden beds.

Composting for new garden bedsComposting for existing garden beds
First, apply compost to the soil surface (about 3 to 4 inches, Feel free to add amendments like lime and N-P-K fertilizer. Mix all these within the top 8 to 12 inches of soil using your digging tools if necessary. Apply a thin layer of compost (about a quarter to an inch deep) to the bed surface of the garden beds yearly. Feel free to add the same amendments mentioned in the new garden beds. Next, mix within the top 8 to 12 inches of soil using your digging tools.

Specific for raised garden beds with retaining walls, it may be good to fill them with soil mix and not just compost independently. Ensure to mix the soil thoroughly and as deeply as possible, then move on to installing your plants in the bed.

It might also be helpful to check the quality indicators of your compost,(source) and they are as listed as follows:

  • pH of compost
  • Soluble Salts
  • Nutrients present
  • Moisture content
  • Organic Matter within
  • Particle Size of compost
  • Stability of decomposition and Maturity of completeness of compost
  • Foreign Materials
  • Trace Metals
  • Pathogens

I wrote an amazing guide to compost! It further explains what it is, more tips and tricks, video tutorials, and what to do and not to do so that you too can make nutrient-dense compost at home each time, every time without the smelly mess.

Topsoil or Garden Soil Management

Good topsoil takes years to produce and is thus exceedingly difficult to reproduce at scale. Therefore, though it is not always possible to control flooding, an effort must be made to curb its impact on your garden.

Look into Flood Control to protect your garden soil or topsoil

Floods can strip your garden of valuable topsoil. We have listed out some ways below to combat this problem.

Boost plant growth by aerating your topsoil or garden soil

This allows nutrients to reach the plant’s roots. But remember, you want nutrients to reach the roots without loss of moisture, so do not fully turn the ground.

Cover the topsoil or garden soil surface with mulch

After you have aerated the ground by spiking it with a fork or spike roller, cover the surface with a mulch compost mix. This creates a nutrient store at the top that will seep into the roots when watered and prevent water evaporation.

Spread Glass clippings on the garden soil or topsoil

Add grass clippings as a mulch-fiber over the surface of the topsoil. The fiber in the grass further binds the soil, feeds it, and promotes its ability to hold water. Repeat this process twice a year in Spring and Fall.

Plant along contour lines of your topsoil or garden soil

Plant trees, shrubs, and other plants in rows that follow the contour lines of the garden. This will help prevent your topsoil from being eroded. The objective is to reduce the speed of the flow. Ideally, you want the water flowing in your garden to be low and slow. Shrubbery and trees make this possible.

Soil stability of garden soil or topsoil is important to consider

Keep the top three inches of your soil stable. This means that special attention needs to be paid to newly worked beds and surfaces, ensuring they are protected while still very loose. Also, adding stepping stones in the bed on which to walk.

Quick repairs here and there must be made on the topsoil or garden soil

Repair any erosion as soon as possible to prevent the formation of flow channels which will deepen with time. Consider placing flow-disrupting barriers like large stones at places where water flows strongly due to steeply sloped surfaces.

Consider Crop Rotation on the topsoil or garden soil

Effective rotation planning balances the management of beds on an annual and a multi-year basis. Annual decisions tend to prioritize production concerns. Multi-year decisions tend to prioritize and accommodate biological demands.

The rotation of botanical families prevents the buildup of pest populations by (a) interrupting pest life cycles and (b) altering pest habitats.

Alternatively, beds may be deliberately rotated through a fallow to manage a weed or pest problem.

Conclusion on the difference between topsoil and garden soil

As William Shakespeare’s Juliet Capulet said: “A rose by any other name would smell as sweet.” The soil in your garden that you use to cultivate your produce or flowers is all topsoil. It is also garden soil. May you use it optimally, care for it, evoke its full potential.

Add some care, have it analyzed and supplement what it needs so that it has the capacity to return your investment into it a hundredfold. It is a precious substance made all the richer by the “sacrifice” of other plants, adding to its capacity to yield in abundance. Take care of it, and happy growing.

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Tony O'Neill

I am Tony O'Neill, A full-time firefighter, and professional gardener. I have spent most of my life gardening. From the age of 7 until the present day at 46. My goal is to use my love and knowledge of gardening to support you and to simplify the gardening process so you are more productive

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