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What is Potting Soil?

There is a lot of confusion over the term potting soil, and other terms that are commonly used in horticulture such as potting mix, compost, etc… but understanding what these terms mean is essential if we are to choose the right growing medium for our plants.

potting soil

What Does Potting Soil Mean?

Potting soil is the term used to refer to a manufactured growing medium used to fill pots or other containers when growing plants. The term was first used in print in 1861, in an issue of ‘American Agriculturist’ and since then, has led to a lot of confusion among new gardeners. 

Much of the confusion arises from the fact that this is a term used loosely, and it is not always used to mean the same thing. 

What is the difference between potting mix and potting soil?

Potting soil can also be called a potting mix, and the two terms are often used interchangeably. However, in some cases, the term potting mix is used to refer to a soil-less blend while potting soil is used for mixes that do contain soil in the composition. 

The terms are used somewhat differently in different contexts and parts of the world. And in the British Isles, the term potting compost is another synonym. 

Some commercial potting soils or potting mixes that you can buy are quite simple, with very few ingredients, while others are much more complex with a far longer ingredient list. And, when it comes to quality, it is important to understand that not all potting soils were created equal. Some are much better than others. 

What is the difference between garden soil and potting soil?

The term, since it contains the word ‘soil’ is rather misleading. Many potting soils or potting mixes are completely soil free. 

It is not always a good idea to use just garden soil to fill your pots in a container garden. You can use soil from your garden in some instances, mixed in with other ingredients such as homemade compost and leaf mold. But garden soil on its own won’t be ideal for container cultivation. 

Garden soil is made up of minerals (sand, silt, or clay…), organic matter, air, and water. Soils in different areas vary in the size of the minerals they contain, how much organic matter is in them, how aerated or compacted they are, and the amount of moisture they retain. 

Like garden soil, potting soil or potting mix contains organic matter, which, as it breaks down, provides some of the nutrients that plants need. 

However, unlike garden soil which forms naturally over time, a commercial potting mix or potting soil has been specially formulated to provide plants in pots or other containers with what they need. 

Garden soil is not ideal on its own for filling containers because it can easily become compacted and lose aeration, and is often too heavy on its own for growing most potted plants. 

What is the difference between compost and potting soil?

Though potting soil is sometimes referred to as potting compost in the British Isles, potting soil is not the same thing as compost. 

Good gardeners should understand how to make compost at home. Even when you are only gardening indoors, there are many small-scale home composting options you might consider – from small hot composting bins to vermicomposting, with the aid of special composting worms. You might also ferment food with a bokashi bucket system. 

Homemade compost is useful in any garden and is also a great way to eliminate food waste ending up incinerated or in a landfill. But on its own, it is not the best way to fill pots. 

Compost is one ingredient often used when making DIY potting mixes. For example, to avoid buying a compost mix you can use homemade compost mixed with loam, leaf mold, or other natural ingredients. But on its own, when used to fill pots, compaction or drainage issues may occur. 

Types of Potting Soil

To further understand what potting soil or potting mix is and is not, it is important to look at the ingredients that it contains. This will vary depending on what type of potting mix we are looking at. 

Many potting mixes contain peat. Unfortunately, using peat in your garden is a choice that harms the environment. 

Peat comes from peat bogs – precious wetland ecosystems that are important carbon sinks and biodiversity hotspots, important in freshwater security and water filtration. It should be kept in the ground. 

Fortunately, there is a growing awareness of this problem and peat-free potting soils are now available that are better than ever before and which can compete with the traditional peat-based potting soil options. 

Once you have decided to choose a peat-free option, however, the decisions you need to make do not end there. 

Another thing to decide is whether you will use soil-based (also known as loam-based) or soil-less potting soil in your container garden. As the name suggests, soil-based mixes contain some soil or loam, while soil-less options use other ingredients. 

Multi-purpose potting soils or potting mixes are used to grow a wide range of plants, with a composition that is suited to general cultivation and not for niche needs. 

But some plants require a special potting mix – one that caters to their specific needs. For example, there are potting soils available for ericaceous plants (with a more acidic pH level), and especially free-draining potting mixes for plants like cacti and succulents – to give a couple of examples. 

There are also special seed-starting potting mixes that are especially light and friable, well-suited to sowing seeds and growing seedlings early in their lives. 

Do You Need To Buy Potting Soil?

Commercial potting soils or potting mixes often contain synthetic ingredients, or ingredients from extractive industries (like peat, or mined/quarried materials). 

They may often contain harmful fertilizers that are not in keeping with organic gardening and which are, for ethical reasons, best avoided. 

For this reason, it is important to choose carefully if you do decide to buy potting soil for your container garden. 

Whether growing inside or outdoors, it is better if, rather than buying potting mix, you consider making your own. Remember, you do not necessarily need to buy in the potting medium, as you can create your own mixes that are ideal for the plants you grow. Often you can do so using only natural and readily-available materials from close to where you live.