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Soil testing is arguably the single most important step that a gardener or grower can perform to ensure bountiful yields. Without knowing the pH or current nutrient levels of your growing space, you can easily waste hundreds of dollars on amendments that won’t benefit your soil or crops because they can’t use them effectively. Soil testing need not be a mysterious or daunting task. For less than $30, you can either do it yourself or have a lab analysis of what’s in your soil, complete with recommendations of what your soil needs.
Most local garden centers and even big-box stores sell a variety of inexpensive kits to both test your soil’s pH and determine at least the level of the nutrients that your plants need most, the macronutrients. These kits will often come with recommended nutrient levels and are usually quite user-friendly. The benefits of the do-it-yourself kits are that they’re cheaper than a lab analysis and you get the results right away. The trade off, however, is that these kits are not usually as accurate as a professional analysis.
You may not require a full soil profile, but getting this done at least once before growing food crops is beneficial for knowing exactly what you have in your soil. Check with your local cooperative extension for information about soil testing. If they don’t do it at their location, they can provide you with the names and contact information of reputable labs that offer soil testing services.
Here are three important things that a soil test can tell you about your garden.
Knowing your soil’s pH is the key to understanding what nutrients will be absorbed in your soil. Many soils have the appropriate amount of nutrients, but because the pH is too high or too low, these nutrients are not available to the plant. Think of pH as a highway for nutrients. If the highway passes through where you need to go but there are no on-ramps to get you on it, it doesn’t matter where that highway is.
Most plants do best when the pH levels are between 6.0 and 6.5. This is, of course, a general statement as many plants do better in pHs that are higher or lower. Blueberry plants, for instance like an acidic environment which is achieved when the pH is between 4.5 and 5.5. Some herbs, like Salvia and Sage prefer an alkaline environment between 7.0 and 7.5. For the most part though, crops do best in between 6.0 and 6.5 because most of the nutrients that they need to thrive are readily available in that range.
Many urban growing sites, particularly those on previously vacant lots, may be harboring toxic levels of heavy metals in the soil. A soil test is important to know what is present. The presence of heavy metals in trace amounts is not always cause for concern—plants and people alike need certain amounts of iron, manganese, copper and zinc—but arsenic, lead and cadmium are metals that you don’t want to find.
Your garden site need not have been industrial to be concerned about metal levels. Many landscape materials and children’s play sets have been constructed of wood treated with heavy metals to slow down their decomposition. Used railroad ties are commonly used for retaining walls. These, too, have been treated with toxins such as coal tar, creosote or salts of heavy metals.
Along with testing the soil’s pH, testing for the presence of heavy metals should be a first step before considering the production of any edible crops. If metals are present at hazardous levels, remediation must occur before you can grow food there. This could be physical removal of the soil and replacement with clean soil, or allowing the site to remain fallow and introducing non-edible crops that can remove the toxins. Fungi can also be intentionally spawned to pull out heavy metals from the soil. Before attempting any measure of remediation, be sure to check with the appropriate local and state authorities as this is a regulated activity. Your local extension office should be able to offer guidance with this process, as well.
Macronutrient And Micronutrient Levels
A soil analysis will tell you how much of any given nutrient that you have in your soil. This is helpful to know once you are familiar with the various roles that the different nutrients play and how they are absorbed. Your plants will need nitrogen (N), phosphorous (P) and potassium (K) in higher quantities than the secondary macronutrients, calcium (Ca), sulfur (S) and magnesium (Mg). Smaller amounts are needed of the trace or micronutrients, boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo) and nickel (Ni), but they’re still important for proper plant functions.
Most do-it-yourself kits do not test for micronutrient levels, so you’ll need to get a lab analysis. Most soils, however, contain appropriate levels of the trace nutrients, and deficiencies are less common than for the primary and secondary macronutrients.
It is not the presence or absence of any one of these factors that will give you prize-winning tomatoes or mouth-watering fruits. It is the combination of all of these factors in their proper proportions that combine to form the symphony of a proper growing environment that only a soil test will allow you to know that you have achieved.