This post is guest written by Growing Solutions Farm lead grower and operations manager, Tucker Kelly.
Basketball players spend all their time looking up, looking at the hoop. A sign of a decent basketball player: they don’t look down when they dribble. It’s the opposite for farmers. We spend all our working lives on one patch of earth, staring straight down.
What are farmers looking at? Soil of course. And don’t call it dirt. In fact, if you call it dirt, a farmer will tell you it’s so much more than that.
Merriam Webster defines dirt as “a filthy or soiling substance (such as mud, dust, or grime).” Now, even though farmers like soil, not dirt, I wouldn’t go as far as to use such harsh language. If I had to give you a definition off the top of my head, I would say dirt is composed of largely inorganic components that are by no means conducive to supporting plants. Soil, on the other hand, is an ecosystem unto itself, composed of the organic and inorganic, the micro and macro, as well as flora, fauna and fungi. That’s what farmers are looking down at.
For those interested in gardening or farming at home, eventually, you’ll have to consider looking down the way farmers do.
If you get into soil science, you’ll very quickly bump into the realms of chemistry, plant biology, and microbiology. But a working knowledge of these sciences is not necessary to understand the basics of soil and how it works. There are just a few measurable qualities to look at, either through lab-testing or eye-testing: soil condition, water retention, color, pH, nutrients and contaminants. We’re checking these variables because we want to ensure that our plants have the ideal growing conditions.
Physical Qualities
The physical qualities of soil – condition, water retention, and color – are measured best by eye. These three qualities overlap like Venn diagram, with the center indicating quality soil.
Condition refers to how friable, or crumbly the soil is. It’s related in part to the size of the particles that make up the soil. Soil should not blow away like sand, have so many large particulates that water drains right out, nor should it compact, forming mud when wet. The best soils allow for air to reach plant roots, yet you should be able to form a ball with it in your hand when wet.
Quality soil retains moisture. Water retention is tricky, because hilled rows, raised beds, and swales will affect retention and therefore your schedule for watering. For those of us in Chicago, we should be raising our beds and taking precautions due to likely soil contamination by physical (shards of glass, waste fill, etc.) and chemical contaminants (lead is the big one).
When gardening in raised beds, we have to do two things well: water frequently and make sure we have a lot of organic matter – the best substance for water retention – in our soil. Like condition, soil with good water retention will form a ball in your hands when wet.
Lastly: color. High-quality soil resembles coffee grounds in color and condition – dark, rich, and friable.
Just a reminder: while some may add coffee grounds directly to their soil, coffee is incredibly acidic and must be steeped thoroughly before use. Also, it will not provide any immediate fertilization because microbes haven’t had the opportunity to decompose the materials, which makes nutrients bioavailable.
Chemical Qualities
pH refers to how acidic or basic a substance is. Some plants love slightly alkaline (basic) soil –clematis, cucumber – while others love slightly acidic soil – rhododendron, tomato. The keyword here is slightly. Most plants like a pH between 5 and 7. Soil exceeding this range in either direction would not be conducive to growing without buffering – the addition of material to adjust the pH.
Nutrient qualities of soils can vary widely. There are the macronutrients we track and apply frequently, like nitrogen phosphorus and potassium, and the micronutrients that are much harder to assess without performing a soil test. Trust me, you’ll notice if your soil isn’t right in the sweet spot at the center of the Venn diagram.
Contamination is the most consequential concern we have. Contamination by heavy metals is most likely and can come from all kinds of residential or commercial development. Chemical contamination can come from underfoot, overhead (as acid rain), and can also leach into groundwater. This is why the City of Chicago, as well as many environmental advocacy groups suggest that you raise your beds, bring in soil, and, if you can, purchase a geotextile fabric that will prevent chemical contamination from leaching upward into your imported soil from the ground below.
All three of these chemical qualities are just as important as the physical qualities of soil, but there isn’t a simple test like balling the soil when wet. For an accurate evaluation, you’ll have to take a soil sample and send it to a lab. The University of Illinois Extension and the Cook County Farm Bureau have listed a number of accredited laboratories that can perform this panel of soil tests for a fee.
Mitigating a pH imbalance, nutrient deficiency, or contamination can be done with agricultural inputs, but fixing your soil through remediation – from the ground up – should be your goal. You should test your soil before your remediation efforts to help determine what you need to do to improve the soil. You should also get your soil tested after to ensure you’ve achieved your goal.
Flora, Fauna, and Fungi
In as few, clear words as possible: soil should have creepy crawlies in it.
Remember, the organic component – living or not – defines soil. The thoroughly decomposed organic matter, called humus, is where the bioavailable nutrients are found which your plants need to grow up healthy. The abundance of humus is directly related to the quality of soil condition, water retention and color, and provides superficial information on nutrient quality.
When we talk about the living component, we’re talking about bugs, fungi, and microscopic organisms. Microscopic organisms are the unsung heroes of soil, simply because we can’t see them. Microorganisms make the humus – they are fixing the recently living organic matter into simpler, bioavailable organic matter that plants can use. When we steward this process, we call it composting.
Organisms we can see like worms and fungus, help decompose organic matter to create humus and their presence tells us our soil is healthy, that it’s safe. Soil too acidic or alkaline would drive the organisms away or kill them. Contaminated soil would do the same. Remember, soil is an ecosystem unto itself. Our soil is to these organisms the same as how the water in Lake Michigan is home to its inhabitants. The presence of these organisms functions superficially as the only true eye-test we have for the chemical qualities of our soil.
I may have fibbed a bit when I said farmers were looking at soil. If I didn’t fib, I was speaking in half-truths. Farmers are looking at soil and they aren’t. Soil is soil, but soil is also an ecosystem, a mosaic or gestalt much greater than the sum of its parts. That’s what we’re looking down at.
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