Shopping for a growing medium for potted plants can be confusing because “potting soil” and “potting mix” are terms often used interchangeably. Potting soil and potting mix are different, depending on what you need them for, whether for potting or repotting container-grown plants, starting seeds, or adding soil to a garden bed.
Here are the key points when deciding about using potting soil vs. potting mix so you know you're getting the right product for your purpose.
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What is Potting Soil?
Potting soil is very often sold as "garden soil," and is labeled "for in-ground use." Quality bagged soil products are formulated to mimic the components of the best natural soils in the ground.
Uses of Potting Soil
True soil is generally not used for ordinary container gardening, but it is sometimes used to fill large raised beds, especially when the existing soil in a yard is of poor quality.
Common Ingredients of Potting Soil
Potting soil products contain true dirt, including mineral elements such as sand, clay, and loam. Bagged potting soils are often mixed with compost to improve their nutritional value.
What is Potting Mix?
Potting mixes do not contain any dirt. These bagged products are sometimes labeled "soilless mix" or "soilless medium."
Uses of Potting Mix
Potting mix is the standard product used for most container gardening, both indoors and outdoors.
Common Ingredients of Potting Mix
Potting mixes contain organic materials, such as peat moss, with additional elements to improve drainage. They sometimes contain slow-release fertilizers as a component.
What Is Potting Mix vs. Potting Soil?
When purchased as bagged products, potting soil is much different than potting mix. When shopping for a growing medium, read the label to know what you are buying. When the ingredients are not listed, the bag's weight is usually a good indicator because true soil will be 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 |
| Usually based on in-ground soil (dirt) | 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, sphagnum moss, aged bark (pine bark), coir (from coconut husks), pumice, perlite, or vermiculite |
| Often contains organic compost | Might contain slow-release starter fertilizer or other fertilizer |
| Heavy | Lightweight and fluffy |
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How to Choose Between Potting Soil vs. Potting Mix
Container Gardening
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 soilless 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.
Non-Container Gardening
When choosing a growing medium for non-container gardening or in the landscape, use potting soil (often packaged as "garden soil"). It can also sometimes be used to fill large raised beds or large elevated planters. Note potting soil contains true mineral soil and can become compacted, dense, and water-soaked. While potting soil might provide 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.
Tip
Frequent watering flushes out nutrients even from soilless potting mixes with added fertilizer. To keep heavy feeders healthy and vigorous, identify plants with specific fertilizer needs and amend the potting mix with food.
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Why Potting Mix is Better for Aeration, Weight, and Drainage
Potting mix is the medium of choice for nearly all container gardening for three reasons: aeration, weight, and drainage.
- Potting mixes are fluffier growing mediums, which allow water and air to better penetrate the roots in the confined area of a container. This fluffiness makes for better root aeration, which is essential to the health of plants.
- This fluffiness also improves drainage and prevents roots from stagnating in water, which can cause root rot.
- Finally, the fluffy, airy nature of a potting mix also makes potted plants lighter in weight, which can be an important consideration if you are moving large potted plants around a patio or deck.
True soil, by contrast, is typically much heavier and denser than a potting mix. When used in containers, garden soil typically holds too much water to allow the roots to breathe and drain effectively.
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Different Types of Potting Mixes
For most container-grown plants, use a standard all-purpose potting mix but some plants require exceptionally good drainage or a higher or lower pH. For these special conditions, purchase potting mixes formulated for specific types of plants, such as the following:
- 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 airflow 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 mixes, which also contain 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 are 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 blood meal 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 sphagnum moss, coir, and wetting agents such as a non-toxic polymer.
Checklist
Here's a quick recap of key distinctions between potting soil and potting mix:
- Potting soil is true dirt that mimics the best soil.
- Potting soil is used in the landscape.
- A bag of potting soil is heavier than a bag of potting mix.
- Potting mixes do not contain any soil.
- Potting mixes are used for container planting, especially for orchids, succulents, and cacti that need good drainage.
- A bag of potting mix is lighter than a bag of potting soil.
FAQ
Does potting soil go bad?
Potting soil doesn't technically go bad but the quality and nutritional value of the soil may diminish over a year. Rejuvenate old potting soil by adding fertilizer and compost.
Can you reuse potting soil?
You can reuse potting soil only if the plants that grew in the soil before were healthy and vigorous. Do not reuse potting soil that was used with unhealthy plants.
Do you need to add fertilizer to potting mix?
After planting with potting mix, it's a good idea to add an all-purpose fertilizer. However, know your plant's needs so you don't overfeed or underfeed it.
Can you use potting mix as potting soil?
It's a good idea not to use these products interchangeably. Soil-free potting mix is for containers and potting soil is formulated for in-ground use. Using potting mix in the ground won't hurt plants, but potting soil better supports plants growing in the ground.
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