A great garden starts with great dirt. And if you’re looking to purchase that dirt for your garden or containers, you’re not alone. About half of all gardeners in the U.S. purchase soil for their gardens. That comes out to a lot of dirt–about 154 million cubic yards annually.. Whether you’re looking for beautiful blooms or hoping for an abundant vegetable garden, your plants will thrive best when they have a strong foundation in healthy, rich soil. But there are some red flags to look out for when you’re bringing purchased soil home for your garden, from unsustainable ingredients to chemicals that can actively damage your plants.
The Dirty Details
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To get the real dirt on dirt, we talked to Adam Schwartz and Sarah Murphy, the team behind Dirtcraft Living Soils. Dirtcraft was founded in 2018 in Western North Carolina by Adam and Sarah, and specializes in building healthy soils. How do you know what’s in the soil at the store? Look for an ingredient list, ask at your local store, or look online for more information.
Going Peat-Free
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Peat, the surface organic layer of a soil that consists of partially decomposed organic matter, is a common ingredient in commercial soil to make the soil lighter and help it retain moisture. But using peat has some big environmental costs. “In order to harvest peat moss, which is growing in the northern wetlands, permafrost area, you have to drain the wetland, which destroys it,” explains Schwartz. “And when you drain and strip mine that wetland, you’re emitting a whole lot of carbon.” Peatlands actually store more carbon than all other vegetation types in the world combined, so preserving them is crucial to mitigating the effects of climate change.
The Best Peat Alternatives
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So, what to use instead? “One ingredient that we promote that is really good for the climate is compost, especially food waste compost,” says Schwartz. “Because you’re taking wasted food that would otherwise go to the landfill, where it’s generating methane emissions. When you compost it, you’re actually recycling that carbon into an ingredient that does help build soil and does promote beneficial biology. It’s good for plant health, so it’s one way to replace some of the peat moss that’s being used.” Another popular peat alternative is coconut fiber, which is a renewable resource that’s a byproduct from the coconut water industry, Schwartz said.
Look Out for Perlite & Vermiculite
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Perlite and vermiculite are common additives you’ll see in commercial soil that are used for water drainage and retention, respectively. However, because both of these ingredients are mined, they carry some environmental baggage as well. One alternative to consider is rice hulls. “That is a more sustainable option,” Schwartz says, although he cautions it doesn’t work for every application.
The Truth About Biosolids
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Biosolids are particularly important to look out for, but sometimes they can be tricky to identify. “Biosolids are found in almost all big box store potting soils and soil amendments,” Schwartz said. While those products may seem like a great deal, there’s a reason they can be so inexpensive. “The reason is because they’re trying to offload a byproduct they don’t have an outlet for, and that product is biosolids,” Schwartz explains. “Which is literally just poop.” And that can even include human waste, as well, Schwartz says. “It’s potentially got manures from big CAFOs (confined animal feeding operations) in it. And sometimes it’s got ‘municipal sludge’ in it, which is byproducts from sewage treatment plants.” Yuck.
Avoiding the Sludge
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Now, before you totally freak out that you’ve been growing your vegetables in poop all this time, keep in mind this use for treated sewage sludge has been approved by the EPA, and it has to meet “the most stringent pollutant, pathogen and vector attraction reduction requirements” before it can be sold for gardening purposes. But that doesn’t mean it’s necessarily good for your plants, Schwartz says. So, how do you avoid biosolids in your soil? “Biosolids can’t be certified organic. So that is one way to avoid it,” Schwartz says. “If you go for the organic label, then you’re not going to be getting the sewage sludge.”
The Trickery of Synthetic Fertilizers
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Popular and easily-acquired fertilizers like 10-10-10 or NPK fertilizers may initially seem appealing, but they aren’t great for the long-term health of your soil, or your plants, according to Murphy. “It’s a chemical, it’s soluble. It adds fertility quickly, and then passes through the soil,” Murphy explains. “It washes through, ends up in waterways, and is not truly feeding the soil.” It’s kind of like spoon feeding someone corn syrup, Schwartz says. “You’re giving it a big energy boost, and then it can kind of get addicted to that, and the plant won’t develop the biological relationships that are in the soil that it needs later in life,” he says. Synthetic fertilizers are also salt-based, which can cause additional stress on the plant. “In addition to the trickle down environmental effects of it, you’re creating osmotic stress on the plant, so it is not able to uptake water and regulate water correctly,” Schwartz says.
Manure Mindfulness
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If you’re thinking of supplementing your garden soil with some manure, you may want to opt for cow manure over horse manure. The reason? Herbicides. “What’s considered high end animal feed would be the hay that has no weeds in it,” Schwartz says. “But honestly, that’s the material that’s been sprayed the most. Cows have four stomachs, and so they do a decent job at breaking down the herbicides. But horses, it kind of just passes right on through.” Unless you know the horses your manure is coming from–and what they eat–you’re going to be safer with cow manure. “Make sure it’s composted as well,” Schwartz adds. “You don’t want to put it on fresh because that could burn the plant just from the nitrogen and ammonia.”
Other Herbicide Hiding Spots
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Harmful herbicides can also be present in grass clippings and other yard waste used for gardening. “Herbicides are so easy to access now; a home gardener can go to a hardware store and purchase really industrial strength herbicides, right, and spray them all over their lawn,” Schwartz says. “That grass gets cut and it ends up getting brought to a municipal composting yard that’s accepting yard waste, and then that material bioaccumulates in the composting process.” The result? “You end up with something that’s got high concentrations of herbicides in the soil itself.”
Building Blocks for Healthy Soil
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So, what ingredients should you focus on when looking for healthy soil for your gardening projects? It’s all about promoting life in your soil. “Soil is a delicate balance of soil life, and microbes are an important part of that soil life,” Murphy says. “And if you don’t have life in the soil, you are not going to have happy plants.” Schwartz offers a simple trick to figuring it out. “Look for ingredients that are really easy to understand what they are, that are just raw parts of things found in nature,” he says. “That’s what we focus on, because those ingredients are going to be really digestible by the biology of soil, as opposed to synthetics.” Schwartz and Murphy use ingredients like single-source meals–one ingredient that’s been ground up and processed, like crab, alfalfa, or kelp.
An Organic Shortcut
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If you’re starting to feel like troublesome ingredients are lurking in every bag of potting soil, keep in mind that many of these issues can be avoided by purchasing organic soil. Soil that has been certified by entities such as the USDA’s National Organic Program or the Organic Materials Review Institute is required to meet certain standards that can help you weed out problem ingredients. “In addition to saying biosolids are not organic, or synthetics are not organic, they do have limitations on how much heavy metal can be present in soil, as well,” Schwartz says. The organic label won’t eliminate every questionable ingredient–peat is organic, for example–but it can be a good place to start. Prepare yourself with good information and use your critical thinking skills when you set out to purchase garden soil, and you’ll set yourself up for greater gardening success, with healthier soil and happier plants.
