Buying Soil For Your Garden? Read This First

Whether marketed as topsoil, black soil, black earth, or some other catchy phrase, it’s not easy to know what’s in the bag. Use these tips to help guide your soil shopping decisions.

If you need help figuring out how much soil to buy, use our free soil calculator. It works for bag and bulk purchases and provides estimates for garden beds, raised beds, and containers.

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Soil Shopping Tips

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 in this context.

Some products do list a “guaranteed minimum analysis” when organic material is included (N-P-K or nitrogen, phosphorus, potassium) so that’s something—but most of us don’t know what the numbers mean.

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 garden 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.

Contents

Soil Basics

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”.

The rest of the container can be filled with less expensive (harmless) fillers. This article on How To Fill Tall Raised Beds And Save On Soil has lots of ideas.

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 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 Look For

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.

You can’t judge a soil by the buzzwords on its packaging.

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 soil 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.

Frequently Asked Questions

The ingredients included:

Wow, right?

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.

Summary

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.

Resources

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~Melissa the Empress of Dirt ♛