Shopping for a growing medium to use for potted plants can be a confusing experience because the terms “potting soil” and “potting mix” are often used interchangeably. They are indeed two different things and depending on what you need them for—potting or repotting container-grown plants, starting seeds, or adding soil to a garden bed, you need to make sure you get the right product for your purpose.
Here are the differences between potting soil and potting mix as well as other useful tips about various potting mixes formulated for specific plants.
Click Play to Learn the Difference Between Potting Soil and Potting Mix
What Are the Ingredients in Potting Soil and Potting Mix?
Potting soil and potting mix (which is soilless, and is often referred to as soilless potting mix) have some key differences. When shopping for soil, read the label to know what you are buying. When the ingredients are not listed, the weight of the bag is usually a good indicator because the soil contained in potting soil makes it much heavier than potting mix. Don’t be tempted by the colorful design on the bag. If the bag doesn't list ingredients, don’t buy it.
|Comparison of Potting Soil and Potting Mix|
|Potting soil||Potting mix|
|Might or might not contain garden soil and sometimes sand||Soilless: does not contain any soil. Often labeled as soilless mix or soilless medium|
|Not sterile; can contain pathogens such as fungi or other diseases. Might contain weed seeds.||Sterile; makes it safer for plants because it doesn't contain pathogens that cause disease|
|Contains minerals and organic matter||Contains components to improve aeration and drainage such as: peat moss, spaghnum moss, aged bark (pine bark), coir (from coconut husks), pumice, perlite, or vermiculite|
|Contains compost||Might contain slow-release starter fertilizer or other fertilizer|
|Heavy||Lightweight and fluffy|
Which one to use?
For container gardening, both indoor and outdoor potted plants, as well as seed starting, use only soilless potting mixes. Their special combination of ingredients ensures that the mix retains moisture and won’t compact to allow enough air space for tender roots to grow. Also, in sterile soillesss potting mixes, plants or seeds are not exposed to disease pathogens or weed seeds. A soilless potting mix is a much more controlled growing medium than potting soil.
For non-container gardening and landscape use, use potting soil. Keep in mind though that potting soil, because it contains soil and sometimes sand, can become compacted, dense, and water-soaked. While potting soil might contain a good amount of nutrients from the compost it contains, you will still have to add other amendments to improve overall soil texture and drainage.
The frequent watering of containers flushes out nutrients and some plants, especially edibles, are heavier feeders than others. Just because a soilless potting mix might have added fertilizer, it does not guarantee that it will keep the plant healthy and vigorous during the entire growing season. One of the most common container gardening mistakes is underfeeding your plants.
Different Types of Potting Mixes
For most container-grown plants, you can use a standard all-purpose potting mix but some plants require exceptionally good drainage or a higher or lower pH. For these special conditions, you can purchase potting mixes formulated for specific types of plants.
- Orchid potting mix: All-purpose potting mix retains too much water and too little air for orchids. Specialized orchid potting mix contains bark to drain well and create air flow that orchids require.
- Succulent and cactus potting mix: The sand in this type of potting mix ensures the fast drainage that is key for growing succulents and cacti. A variation of this is cacti, palm, and citrus potting mix, which also contains recycled forest products and pH adjusters such as oyster shell lime to keep the potting mix at a slightly alkaline range.
- African violet potting mix: A specially-formulated potting soil with pH adjusters such as dolomitic lime that meets the slightly acidic pH requirements of 6.0 to 6.5.
- Organic potting mix: A wide range of organic potting mixes available. Look for the OMRI (Organic Materials Review Institute) label which certifies that everything that goes into the potting mix production is organic. If the mix contains fertilizer, only organic ingredients such as bone meal or bloodmeal are used.
- Moisture-control potting mix: Some potting mixes contain moisture control elements that absorb and retain more water than standard potting mixes due to the addition of spaghnum moss, coir, and wetting agents such as a non-toxic polymer.