When faced with all of the different soil mixes available online and in our favorite garden centers, deciding on garden soil vs potting soil can be a little confusing. After all, there are individual products for potting up orchids, African violets, cacti, succulents, and more. So, how do you tell them apart? And what potential benefits can be attributed to them? To find the answers—and figure out which growing medium might be best for your gardening project—it’s important to understand which ingredients are typically found in both garden soil and potting soil. Then you can fill your garden or container accordingly so the plants, seeds, and seedlings you dig in can thrive.
Why garden soil and potting soil are not interchangeable
Although you may see them referred to interchangeably, garden soil and potting soil are not actually the same thing. They each have different qualities which make them better suited for different uses. For instance, while potting soils are generally lightweight and sterile, garden soils are usually heavier and potentially teeming with life.
What is garden soil?
Used by itself or added to outdoor garden beds, garden soil is topsoil that has been amended with organic materials, like compost, worm castings, and aged manure. As for the topsoil it contains? If you were to dig a couple of feet down into the dirt, you’d find a dark-colored layer—the topsoil—in at least the first few inches. On its own, topsoil is used in landscaping projects like filling in low spots or establishing new lawns. It contains organic matter and, depending on its source, varying amounts of different particle sizes, including silt, sand, and clay.
What is potting soil?
Potting soil is a standalone growing medium often used in seed-starting and container gardening. Potting soils may contain a base of garden soil, aged compost, or composted wood along with non-soil additives. Some of these extra ingredients add structure and support for plant roots. Others help to retain moisture or provide room for oxygen around developing plant roots.
Just to throw another wrench into things, unlike many potting soils, potting mixes—also known as soilless mixes—no contain soil. Instead, these are made up of non-soil additives, like peat moss, pine bark, and mined perlite and vermiculite. (Into organic gardening? Read potting mix labels carefully to make sure the ingredients meet your specific criteria.)
Ingredients in potting soil
Some of the most common ingredients you’ll find in potting soil include non-soil additives like perlite, vermiculite, peat moss, and coconut coir.
- Perlite and vermiculite: Both perlite and vermiculite are naturally occurring minerals that are usually included in potting soils to help with soil structure, drainage, and aeration.
- Peatmoss: For its part, peat moss is another heavily used natural resource. Harvested from peat bogs, the material holds moisture well and improves the growing medium’s texture, too. (Concerned about peat? Keep reading for alternatives.)
- Coconut color: A byproduct of coconut harvesting, coconut coir is a fibrous material that comes from just below the coconut’s outer shell. Coir is a newer potting soil additive that also retains moisture really well.
Incidentally, when deciding on garden soil vs. potting soil, some gardeners’ choices are influenced by sustainability issues. When left undisturbed, peat bogs hold onto large amounts of carbon. Upon harvest, that climate-changing carbon is released into the atmosphere. And, although it’s sometimes floated as a more sustainable option, coconut coir has its own limitations. Because the material is high in salts, coir requires a great deal of fresh water to process for use in gardening.
Recently, gardeners and potting soil manufacturers alike have been experimenting with “greener,” non-soil additives. One promising possibility? Pitt Moss, a growing medium blend made from recycled paper fibers.
The components of garden soil
In part, the overall quality and characteristics of garden soil can vary depending on the ratio of silt, sand, and clay present in the topsoil it contains. That’s because clay soil, sandy soil, and loam soil each have different properties. (For example, while clay-heavy soils retain water and nutrients well, soils with higher amounts of sand will let go of moisture and nutrients more quickly.)
In addition to topsoil, garden soil can contain many different sources of organic matter. Some of these sources commonly include aged manure, well-rotted wood chips, finished compost, or worm castings.
The main differences between garden soil vs potting soil
Understanding the main differences between garden soil vs potting soil makes knowing which one to reach for much easier.
- Rich in organic matter
- Quality and characteristics vary depending on top soil and amendment types
- Heavier than potting mixes
- Contains range of macro and micronutrients, and beneficial microorganisms
- May contain some weed seeds and plant pathogens
- Retains moisture and nutrients
- Provides good support for roots and top-heavy plants
- Contains non-soil additives like peat moss and perlite
- Uniform, lightweight texture
- Sterile (contains no weed seeds or plant pathogens)
- Provides no nutrients (unless fertilizer is added to the mix)
- Doesn’t hold nutrients well
- Retains moisture and facilitates drainage
- Plant-specific mixes (with optimized pH levels) available
The power of beneficial microbes in garden soil
Unlike sterile, soilless mixes, garden soil contains a multitude of tiny, living creatures—soil microbes, including beneficial fungi, bacteria, and nematodes, among others. As these microorganisms naturally break down organic matter in the soil, they increase the bioavailability of nutrients. This, in turn, affords the plants we grow in that soil greater access to the micro and macronutrients they need in order to thrive. The community of microbes living in garden soil also helps to keep certain plant pests and pathogens in check.
Which option is best for starting seeds?
Potting soils made up of soilless ingredients, like perlite, vermiculite, and peat moss or coir, have been developed with seed starting in mind. They facilitate good drainage and aeration, they don’t contain weed seeds, and, because they’re sterile, you’re much less likely to lose new seedlings to disease. Potting soil pH levels are also optimal for seed starting.
Depending on their ingredients and the manufacturing processes used, some potting “soils”—as well as potting mixes and soilless mixes—do not contain the fungi or bacteria that are present in regular garden soil. It’s true that many soil-based microorganisms do have positive effects on nearby plants; however, some are the culprits behind soil-borne “damping-off,” “root rot,” and other diseases. These can ravage germinating seeds, small seedlings, and new plant cuttings.
Potting mixes and soilless growing media also lack seeds from potentially competing plants. As a result, your new seedlings won’t have to share access to water, nutrients, and sunlight with weeds inadvertently popping up alongside them.
What should you use for container gardening?
Some gardeners have strong preferences when it comes to garden soil vs. potting soil—particularly when growing plants in containers. In very large, outdoor pots, garden soil may be more economical.
Still, for indoor container gardens and greenhouse uses, you might want to choose potting soil since it’s less likely to include insect larvae that could hatch. If you do use potting soil in your containers, you may need to fertilize your plants more frequently unless you’ve used a fertilizer-added potting mix.
Which soil is better for making a raised bed vegetable garden?
When I give my talks about raised beds, soil is one of the most popular questions. My recommendations are always to purchase the best-quality soil you can afford. In this case, a garden soil delivery makes the most sense. Part sand, silt, and/or clay and heavily amended with organic ingredients like compost or aged manure, garden soil is a great source of slow-release nutrients. Heavier than potting mix, it also retains moisture better. I will top-dress the garden soil layer with more compost to add even more nutrients to the soil. And for deeper garden beds, I’ll add a layer of sticks and branches, or sod, to fill in the bottom, before adding the garden soil. This article goes into more detail on choosing soil for a raised bed.
Can potting soil be used as a soil amendment in the garden?
You can use potting soil as a soil amendment for especially problematic areas in your garden beds. Need help balancing out compaction from heavy clay soils? In a pinch, lightweight potting soil mixes can help to improve soil drainage and aeration. (Just keep in mind that any perlite or vermiculite that these products may contain won’t decompose in your garden.)
As you become acquainted with some of the most common ingredients found in these products, along with their benefits and drawbacks, you should be able to make better purchasing decisions. You might even begin mixing some of your own custom garden and potting soil blends, too.
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