Which one is better for your garden, potting soil or potting mix? While the two terms are often used interchangeably, they do not refer to the same medium.  The answer to which is better depends entirely on the purpose for which you are going to use it.  This article will discuss the differences between the two growing mediums and the situations for which they are best suited.

Compare the Ingredients

To differentiate between potting soil and potting mix, we need to compare the ingredients.  Know, however, that ingredients in both can vary depending on the manufacturer.  But in general, potting soil simply contains basic garden soil, which is usually comprised of decomposed organic matter, minerals, and nutrients. It may also contain sand.  It is not sterile and therefore may contain fungi, or even worse, harmful pathogens.  You can find out the specific contents of the potting soil you are considering purchasing by reading the list of ingredients on the package label, or if purchasing in bulk, the landscape company or “dirt yard” should be able to provide you with that information.  If they cannot tell you what is in it, you should consider purchasing it elsewhere.

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Potting mix, on the other hand, does not contain any soil and is sometimes referred to as a “soilless mix.”  In lieu of soil, the growing medium contains ingredients that help with drainage and aeration, such as peat moss or sphagnum moss, perlite, vermiculite, coconut coir, and pine bark.  It may also include a slow-release fertilizer or other types of fertilizer.  It is sterile, meaning it is void of disease-causing pathogens and thus, is considered a healthier option for growing plants.  Potting mix is lighter and less compacted than potting soil.

Different potting mixes are available for specific types of plants.  For example, mixes for succulents and cactus, African violets, and orchids are designed to meet the specific soil pH and nutritional requirements of these plants.

Cost

At first glance, potting soil is usually less expensive than potting mix because soil is the only required ingredient.  And soil can be “dirt cheap,” as they say.  Potting mix, on the other hand, is comprised of amendments, which tend to cost more than basic garden soil.  But remember, potting soil may require the addition of certain amendments to help with drainage and aeration, thus, increasing the cost.

Which is Best? Potting Soil or Potting Mix?

Potting soil is better suited for raised beds, although you will more than likely need to add amendments to help with drainage and aeration.  You will also, on occasion, need to add organic fertilizer or compost to refortify it.  (You can learn the difference between fertilizer and compost in this helpful article.)  Potting soil is not conducive to seed starting because it is usually heavy and too dense, which makes it hard for new roots to penetrate the soil.

Potting mix is best for container gardening because its light and airy texture is more conducive to new root development than the heavier potting soil.  What’s more, potting mix drains better, whereas potting soil can become compacted, especially in enclosed spaces like containers.  Compact soil means that the water will have difficulty draining, causing the plant’s roots to become waterlogged, thus harming and potentially killing the plant. 

Like potting soil, potting mix will need to be refreshed from time to time.  However, the latter will require a nutritional boost more often.  Here’s my article on how to refresh and reuse potting mix.

Potting soil and potting mix may be terms that are used interchangeably, however, the mediums are very different with respect to their composition and purpose.  Once you decide where you want to garden, whether in raised beds or containers, you will know which medium to use.

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