Topsoil, Compost, Triple Mix – What’s the Difference?

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Robert Pavlis

Go to any garden center and you will find a large range of products that all look like soil. Many names are used including topsoil, triple mix, compost, potting soil, black garden soil, peat moss and garden soil. What is the difference between all of these products? It can be very confusing.

Some of these products are marked as certified. What does that mean? What kind of guarantee do ‘certified’ soil products offer the consumer?

These and more dirty topics will be discussed in this blog post.

TopSoil, Compost, Triple Mix - What's the Difference?
Components of Ideal Soil, by GardenFundamentals.com

Soil And Dirt – What is the Difference?

The terms soil and dirt are incorrectly used interchangeably. Soil is the stuff out in your garden. Dirt is the stuff you sweep up in the house. The term dirt should never be used for your garden.

What is soil? It seems like such a simple question but many people don’t understand what soil is. Soil consists of the mineral component, the sand, clay and silt, as well as dead organic matter. The living plant and animal life found in soil is NOT part of soil. So the snails, worms, bacteria and fungi are not part of soil. For this reason soil is NOT living. A fact that many people just can’t seem to accept. There is life in soil but soil is not living.

Growing Great Tomaotes, by Robert Pavlis

Most soil-like products are a mixture of minerals and organic matter. In order to understand how and when they should be used it is important to understand the differences between various product terms.

American vs British English

John Innes Compost is a peat-based soilless mix
John Innes Compost is a peat-based soilless mix

In the original version of this post, I made a comment about the use of the word “compost” in the UK and got it partially wrong. I have now clarified things with the British contingent in our Facebook Group: Garden Fundamentals.

In the UK, compost can mean many things. In some cases an adjective is used, such as seedling compost, but the adjective is routinely dropped so that it’s just called compost.

  • Compost – decomposed organic matter from a compost pile
  • Seedling compost (or just compost) – could be a soilless mix or a soil based mix (purchased or homemade)
  • Potting compost (or just compost) – could be a soilless mix or a soil based mix (purchased or homemade). This includes terms like ‘loam-based compost’.

The term compost is usually applied to bags of commercial stuff, even if it is soil-based. Terms like topsoil are used when it is bulk material, or sitting on the ground.

Canada uses many British terms but when it comes to soil, we follow the Americans, and that is what I will do in the rest of this post.

Types of Soil Products

The following is a list of some of the products you can buy. Some are available in bulk and many are sold in bags.

Soil Science for Gardeners book by Robert Pavlis

The definitions I am providing are the most common definitions. These may change from region to region, and country to country. It is also important to know that there are no accepted formal definitions for most of these products. Companies can use any term they want on their products – at least in north America.

Topsoil

Topsoil is the top part of soil that is normally cleared before construction starts. It can be a couple of inches thick or even a foot thick. It is the best quality of soil because this top layer contains most of the organic matter and the living life forms.

When a forest is removed for construction the top soil can be excellent. If a farm is used, the top soil can be of low quality since crops and the farming practices have reduced the organic content for many years.

When it is freshly collected, topsoil is great for a garden since plants grow very well in it. The problem is that in many cases the top soil is collected and piled in large hills until it can be sold. It can take years to sell and by then much of the organic matter has decomposed, and most of the life forms are dead. It is therefore no longer great soil. It still might be better than what you have in your garden.

Topsoil is usually screened to remove rocks so it is easy to work with.

Since topsoil is considered one of the best soils  many companies slap this label on their product. Seeing this name on a bag tells you very little about its quality.

Compost

Compost is made up of partially decomposed plant and animal material – mostly plant. It is recognized as a great way to fertilize plants, which is true. The so called ‘finished compost’ is not really finished. For more details on this see; Compost – What Is Compost. It will continue to decompose for another 5 years and as it does, it releases nutrients into the soil which plants can use.

We have a lot of waste wood around and in recent years a lot of it has been ground up and composted. Wood is a plant product, but it is a plant product that provides very little nutrients. It is good for loosening your soil but it does not do much to feed the plants. Since garbage wood is cheap it is used a lot to make the cheaper compost products.

It contains no sand, silt or clay, so compost only adds the organic part of soil.

Peat Moss

Peat Moss is dead sphagnum moss. As moss dies it forms very deep boggy areas full of the material, which is harvested and packaged into bags or large bails. It is a good source of very loose organic matter and it has become the standard for making potting soil.

Peat moss contains almost no nutrients. It does absorb water well and contains a lot of air spaces, both of which plants need at their roots.

Potting Soil

Potting soil can be any number of mixtures and usually contains a lot of peat moss. It can also include things like perlite, vermiculite and even compost. It is usually very light in weight making it ideal for plants in pots and containers.

Many of the potting soils are sold as ‘soil-less mixes’. For some reason this is supposed to be better, but I don’t understand why. Compared to soil it is lighter in weight, it might be more sterile, and it is almost certainly less nutritious for plants. Plant roots do grow quickly in it provided they get fertilized.

In many cases the manufacturers of potting soil claim that it is sterile. That is really a myth. I have not found a single company that sterilizes the product as they package it. The peat moss they use is relatively sterile as far as weeds go but it does contain microbes.

Triple Mix

In this part of the country triple mix is 1/3 top soil, 1/3 peat moss and 1/3 compost. There are no guarantees that triple mix contains these ingredients or that they are in the right ratios.

Triple mix is recognized as good gardening soil and so the term is misused a lot. You really have to have a close look at the product and see if it meets your needs. It is usually a product that is more airy than your garden soil, so it holds more air and water – which is a good thing. It may or may not be more nutritious depending on the type and amount of compost added. Remember that peat moss is not nutritious.

Black Garden Soil

We all know black soil is good soil, so advertisers take advantage of this and sell us black soil. The ‘black’ part is meaningless and can mean anything but it usually does not mean much.

Don’t pay a premium for ‘black’ labeled soil.

Garden Soil

There really is no definition for garden soil. It could be top soil or triple mix, or peat moss, or just poor garden soil. Or it can be a mix of any of these.

As you will see in my next post, there is no real good reason to buy garden soil.

What is Certified Soil and Mulch?

There are a number of certification organizations around. Some certify soil and some mulch. I have looked at a couple to understand exactly what they certify and so far I am not impressed. In one case it means some lab testing was done, but the product does not have guaranteed limits that need to be met. In another, the certification means almost nothing.

Certification on soil products does not seem to add any real value to the product. You still don’t know what is in the bag.

Selecting the Right Soil

Here are some posts to answer that question:

Soil and Compost – Selecting the Right One

Soil for Raised Beds – Which One is Best?

What is the Best Manure for Your Garden

 

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

42 thoughts on “Topsoil, Compost, Triple Mix – What’s the Difference?”

  1. Thanks for the post but I am still a bit confused about what the Brits refer to when they say “compost”. When I watch Gardener’s World and Monty Don tells me to use compost to plant my tubers, what does that refer to on the Canadian market? Potting mix? A me-made mix of soil and compost? Gaaarggh! Any help would be appreciated.

    Reply
    • It is usually potting mix – of some type. It may contain material from compost pile, but it is not 100% of that material.

      Reply
  2. Grow 10,000 plants in soil with out fertilizer and yes they will grow.

    Use what ever you have on hand and yes they will grow.

    Grow in containers in potting soil and yes they will grow.
    M

    That’s right. But amend your soil, add compost, bone meal, blood meal, feather meal, insect frass etc (Not necessarily all of that but add the fertilizer) and you Would grow better. Growing plants need food.

    Try growing in soiless media (Promix BX, Promix HP, coco coir, rockwool etc) add no fertilizer just water and tell me what happens…right everything dies.

    We can feed people food and people live. We can all eat McDonalds everyday and live. That doesn’t mean it’s right. Just because you can do something doesn’t mean it’s right. Feeding the proper nutrition can make a big difference. It’s same with people. Our elite athletes don’t eat McDonald’s every meal. A lot have specific diets to provide specific nutrition to get to another level. Soilless media is for those plants you want to push to maximum potential.

    Where do you learn about plants? Best are forums and internet. Sometimes it’s a little trial and error if you are fine tuning. Visit a local hydroponic shop and talk to them. For most plants you can follow the nutrient label directions (something’s like orchids only need a 1/4 strength solution of they would get nutrient burn) and achieve better results than in the ground.

    Look into hydroponic growing. Soilless media (Promix BX, Promix HP, coco coir, rockwool etc -all soilless media) is hydroponic growing. It’s not the same as soil based growing. It’s a different beast. Again you can get away with one formula but why would you want to. If it’s about the cost then why not just stay in soil or pots?

    Reply
  3. Okay soulless media isn’t sterile, I didn’t mean it that way. Let me rephrase it. It is devoid of nutrients. When it comes to nutrients it is sterile. It often has bacteria added back, but it is devoid of nutrients.

    As a long time grower I can definitely argue that yes you do need both a grow and bloom formula depending on crop type. Some crops you keep adding grow formula it raises the nitrogen levels to high causing only green growth, or your yield will decline. The reason you need a bloom formula with soil was media is because if things are flowering you shift the nutrient ratio. It can be done with only one formula, you would be defeating the purpose. Soulless media is made to increase growth rates by having the nutrients dialled into each specific need the plant has. You customize your nutrient feed to exactly what the plant can take for maximum growth.

    Reply
    • I disagree that “need both a grow and bloom formula depending on crop type”.
      In the ground I grow 3,000 different plants and don’t fertilize any – they all grow.

      In containers – I use whatever is handy and they grow and bloom.

      But lets say you are right. Where do you get the information you need for two formulations? Except for a very few types of plants – this is not known.

      Reply

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