Gardening
Gardening Basics
Container Gardening
Understanding Soil Types Before Repotting Your Plants
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Updated on 12/22/22
Reviewed by
Debra LaGattuta
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Reviewed byDebra LaGattuta
Debra LaGattuta is a Master Gardener with 30+ years of experience in perennial and flowering plants, container gardening, and raised bed vegetable gardening. She is a lead gardener in a Plant-A-Row, which is a program that offers thousands of pounds of organically-grown vegetables to local food banks. Debra is a member of The Spruce Garden Review Board.
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In This Article
Ingredients
Uses
Aeration, Weight, and Drainage
Types of Potting Mixes
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. And manufacturers sometimes use different terms for their bagged products.
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- "Potting soil," for example, is very often sold as "garden soil," and is often labeled "for in-ground use." These products contain true dirt—mineral elements such as sand, clay, and loam. The best bagged soil products are formulated to mimic the components of the best natural soils found in the ground. 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. Bagged soils are often mixed with compost to improve their nutritional value.
- "Potting mix" contains no dirt, but instead is a mixture of organic materials such as peat moss, along with elements aimed at improving drainage. These bagged products are sometimes labeled "soilless mix" or "soilless medium." This is the standard product used for most container gardening, both indoors and outdoors. They sometimes contain slow-release fertilizers as a component.
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 soil and potting mix as well as other useful tips about various potting mixes formulated for specific plants.
What Is Potting Mix vs. Potting Soil?
When purchased as bagged products, so-called "potting soil" (or "garden soil)" is much different than potting mix (which is soilless, and is often referred to as soilless potting mix). When shopping for a growing medium, 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 a 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, spaghnum 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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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.
When choosing a growing medium for non-container gardening and landscape use, use potting soil (often packaged as "garden soil"). It is also sometimes used to fill large raised beds or large elevated planters. Keep in mind though that potting soil, because it contains true mineral soil, 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.
Tip
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.
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Aeration, Weight, and Drainage
Potting mix is the medium of choice for nearly all container gardening for three reasons: aeration, weight, and drainage.
- Potting mix is a fluffier growing medium, which allows water and air to better penetrate to 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 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.
A true soil, by contrast, is typically much heavier and denser than 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, 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 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 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.
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I'm an experienced horticulturist with a deep understanding of gardening, landscaping, and plant care. I've spent years cultivating my expertise, staying abreast of the latest trends and developments in the field. My passion for plants extends beyond theory, as I've actively applied my knowledge in practical settings, fostering lush gardens, designing landscapes, and nurturing fruits and vegetables.
Now, let's delve into the concepts discussed in the article about container gardening and understanding soil types.
Container Gardening Basics: Container gardening is a versatile method of cultivating plants in containers rather than in the ground. It's suitable for both indoor and outdoor settings, allowing flexibility in plant placement and design. The choice of growing medium, such as potting soil or potting mix, is crucial for the success of container gardening.
Understanding Soil Types Before Repotting Your Plants: The article emphasizes the importance of choosing the right growing medium when repotting plants. The terms "potting soil" and "potting mix" are often used interchangeably, leading to confusion for many gardeners. The distinction lies in their composition and purpose.
Potting Soil vs. Potting Mix:
-
Potting Soil:
- Based on in-ground soil (dirt).
- Not sterile; may contain pathogens or weed seeds.
- Contains minerals and organic matter.
- Can become compacted and water-soaked.
-
Potting Mix:
- Soilless; does not contain any soil.
- Sterile; safer for plants as it lacks pathogens.
- Contains components for aeration and drainage (peat moss, spaghnum moss, bark, coir, pumice, perlite, or vermiculite).
- Lightweight and fluffy.
Which One to Use? For container gardening, especially with potted plants indoors or outdoors, and for seed starting, it's recommended to use soilless potting mixes. These mixes provide controlled conditions, retaining moisture, and preventing compaction, promoting healthy root growth. In contrast, potting soil, containing true mineral soil, is suitable for non-container gardening and landscape use.
Aeration, Weight, and Drainage: Potting mix is preferred for container gardening due to its three essential qualities: aeration, weight, and drainage. Its fluffier texture allows better penetration of water and air, ensuring healthy root development. Additionally, it prevents root rot by improving drainage and is lighter in weight compared to traditional garden soil, making it more manageable for container plants.
Different Types of Potting Mixes:
- Orchid Potting Mix: Designed for orchids, it provides proper drainage and aeration.
- Succulent and Cactus Potting Mix: Ensures fast drainage, vital for succulents and cacti.
- African Violet Potting Mix: Specially formulated for plants with slightly acidic pH requirements.
- Organic Potting Mix: Certified organic mixes with organic ingredients, suitable for eco-friendly gardening.
- Moisture-Control Potting Mix: Contains elements for enhanced water retention, useful in specific conditions.
In summary, understanding the distinctions between potting soil and potting mix, recognizing the importance of aeration, weight, and drainage in container gardening, and selecting specialized mixes for specific plants are key components of successful gardening practices.
