Every gardener will buy soil or soil amendments at some point, but why is this simple task so confusing? What’s the best product to buy? Whether you choose bags or a bulk delivery, there are things to watch out for.
If you are wanting to fill a large plant container, these tips on How To Fill A Tall Raised Bed & Save On Soil are helpful.
Yes, Soil Shopping Is Confusing
While I wish this could be 5 Questions To Ask When Buying Soil For Your Garden with a handy checklist that will ensure you get a product you’re happy with, there is a problem.
The world of soil products and amendments—whether prepackaged in bags or sold in bulk—is pretty much unregulated, and, without consistent standards, it’s a challenge to know what you’re buying.
The goal is simple.
We want something 1) we can afford, 2) that the plants like, and 3) will do no harm.
How difficult can that be?
Well, it turns out it is difficult. We see “topsoil” or “black earth” on the package and assume it must be good. But—surprise—these are feel-good words used for marketing and essentially meaningless. You can read more about this here in Frequently Asked Questions. .
Some products do list a “guaranteed minimum analysis” when organic material is included (N-P-K or nitrogen, phosphorus, potassium) so that’s something—or more than nothing.
Others may voluntarily follow standards from groups like the Compost Quality Alliance (CQA) and put an official-looking seal on the bag. However, interpreting the information and determining whether it matters is another hurdle.
It’s not impossible to find something you’ll like but, the point is, you cannot rely on product labels (or vendor promises) alone. There is no way of knowing what you’ll get or how it will perform just based on what’s listed on the packaging.
Find a local source you trust and use what they use
Short of getting samples analyzed by a soil scientist (ok, not happening), a more realistic option is to find a local, trusted source who can recommend a product they have repeatedly used (so you know it’s consistent), in conditions like yours, for the same sorts of plants you grow.
Otherwise, it’s anyone’s guess. You might end up with something great. You might end up with something useless but harmless. Or—the biggest fear for any organic gardener—you could end up contaminating your soil with who-knows-what or releasing an endless supply of noxious weed seeds that will haunt you for years to come.
To get started, it’s helpful to know the characteristics of good growing medium.
We’re using “growing medium” and “soil” interchangeably here.
For example, let’s say we’re looking for something to use in raised garden beds to grow some flowering annuals and vegetables. Since the top 6 to 12 inches are important for plant roots, that’s where we’ll put “the good stuff”.
So what makes soil “good”?
Healthy Garden Soil
Soil serves several purposes for plants. If the composition is right, it is a source of air, water, and nutrients, and physically helps anchor plants in place.
We’re often buying soil in the first place because the native soil in our gardens is usually not adequate, particularly for containers or raised beds, so the stuff we buy has to offer more of what plants need.
- Texture | While many of our gardens lean toward the sandy or clay ends of the spectrum, a good soil has a loamy texture that is neither too loose nor compacted. This enables both aeration and drainage (but not too fast—you want enough time for the plants to get what they need). One simple test is to squeeze a handful of moist soil and see if it forms a nice, spongy ball.
- Nutrients | Most nutrients come from the mineral content of soil. This is why a soilless mix requires the addition of some sort of fertilizers.
- Organic Matter | To grow plants, soil should be a welcoming habitat for soil life, not a lifeless medium.
While organic matter makes up a small percentage of fertile soil (ideally around 3-5% by weight), it’s vital.
Organic matter (living or formerly living things) provides nutrients and soil structure which in turn helps retain nutrients and moisture.
We also need living things like bacteria, fungi, and nematodes. They help cycle nutrients and get them in a state that plants can use. While most of these are beneficial (or neutral), some do cause diseases.
- Soil pH | A soil pH between 6 and 7 will give us the widest range of plant-growing options. If you’re focussing on plants like blueberries that prefer a more acidic environment, you’d either choose a different growing medium or amend it to alter the pH.
What To Avoid & Who To Trust
Choosing soil is two-fold. We want the benefits but we also want to avoid introducing anything detrimental to the garden.
Pesticides residues, plastic debris, or other garbage, and weed seeds can all come along for the ride. I’ve seen this a lot with bulk distributors who have no interest in ecology or horticulture but simply see an open, unregulated market. That cheap load of “topsoil” may just be a load of dirt and debris or worse.
If you have the chance, spend some time reading soil product labels. It’s kind of shocking how anything goes.
You’ll notice there are a lot of catch phrases that appeal to gardeners. That’s marketing not science.
This doesn’t mean there aren’t good products out there, it just means it’s going to take some work to find them and you can’t judge a bag by its packaging.
I like the idea of a bulk delivery (often sold by the cubic yard) in principle because it avoids all the plastic waste of bags. But bagged products may be the only option if you need a smaller quantity.
My current strategy is to order the same stuff a local, highly-reputed landscaper uses for their clients. They build gardens all over our region and their business reputation depends on it.
What is topsoil?
In soil classification systems, topsoil is the upper, outermost layer of soil. Wikipedia goes on to say it has “the highest concentration of organic matter and microorganisms and is where most of the Earth’s biological soil activity occurs”.
But products sold as “topsoil” are often not topsoil by this definition.
Anyone can use the word to refer to any dirt-like substance.
Yes, you might get soil with some organic matter. We’ve also seen products called topsoil that are soilless.
If you want to know what you’re buying, you’ll need to make enquiries beyond what the label says.
What is black earth?
“Black earth” sounds great, evoking visions of luscious, fertile, dark soil, but what is it? The term has no meaning, other than it’s a soil or soil-like substance that is dark in color (when moist). Color tells you nothing about the value to plants.
What ingredients should I look for when buying soil?
I wish I could say what to look for and send you on your way but that’s only half the battle.
We know a lot about what various soil amendments do, but with no legal requirement to list them by weight, volume, or efficacy—or even label bags accurately—you just can’t know if they are present in any beneficial way.
A product could list worm castings first on the ingredient list but that doesn’t mean worm castings are present in any useful amount.
Items can also be omitted. Say you are avoiding buying peat for environmental reasons. It could still be in the bag but not listed in the ingredients because marketers know it doesn’t mesh with current eco-friendly garden practices.
We’ve found bags saying they contain “one or more of the following” which is the same as “anyone’s guess.”
We’ve also seen expensive bags of “living soil mix” listing every possible wish list item (except soil, oddly enough).
The ingredients included:
- Earthworm castings
- Feather meal
- Bone meal
- Alfalfa meal
- Kelp meal
- Insect frass
- Black soldier fry frass
- Glacial rock dust
- Mined potassium sulfate
Those items check every box (nutrition, water drainage, organic matter…) except they don’t since there’s no way of knowing if they are present in any useful way without more information.
That could be a $25 bag of dirt, garden gold, or anything in between.
And, buying a bunch to fill a raised bed could be a really costly mistake.
What is screened soil?
Some soils and other amendments (like mulch), usually sold in bulk, will list how finely they have been screened. This lets you now what size rocks and other debris you can expect to find mixed in. A rougher medium should be less expensive but has larger items that you’ll need to remove with a rake or sifting screen.
So where does this leave us?
If nothing else I hope I’ve given you a healthy dose of skepticism. You can’t judge the product by the label so you’re better off finding a trusted advisor before risking a purchase.
Ideally, get someone local with a soil science or horticultural background who uses the product on an ongoing basis, grows what you grow, and considers the long-term effects.
It’s nuts it’s this hard to find something trustworthy but it is what it is.
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~Melissa the Empress of Dirt ♛