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This topic might draw some heat, but we’ll be using cold hard facts. As a botanic garden, Idaho Botanical Garden’s role is to connect people to science, specifically the science of horticulture and nature. In our last article we addressed a handful of gardening tall tales. In this article series, we’ll be doing the same. Here’s what we know about organic gardening:

Organic doesn’t mean “chemical free.” A basic definition of organic gardening is home landscape management without the use of synthetic pesticides and fertilizers (AKA chemicals). Some gardeners deem their yards “chemical-free,” which likely means they don’t utilize synthetic pesticides and fertilizers, but for the sake of defining our query it’s important to point out that water is a chemical. No yard is truly “chemical-free.” Even a backyard on Mars would have chemicals present because our universe consists of chemicals.

Mother Nature is a chemist. Synthetic pesticides and fertilizers can and often do mimic those found in nature, but are developed by synthetic chemists in a laboratory setting. However, as the sheer complexity of the insecticidal compounds found in a neem tree will show you, nature is the ultimate chemist. Neem oil is manufactured by compromising the tough kernels of a neem tree and then extracting the oil. For comparison, organophosphates (a common synthetically made insecticide with brands like Malathion and Orthene) are made by reacting phosphoric acid and alcohol. Organically certified pesticides and fertilizers are derived from chemicals already occurring in nature or are shown to be relatively nontoxic, like copper or sulfur.

“Natural” doesn’t mean safe. In the example above, we compared neem oil to organophosphates. Organophosphates have drawn attention for years, and perhaps rightfully so since after their development in the 1930s, they were quickly adapted in World War II to create nerve gas. Nerve gas! Compared to the organic pesticide rotenone (which is derived from a legume), nerve gas doesn’t seem quite so threatening. Repeated exposures to rotenone kills important neurons whose death is associated with Parkinson’s disease. While this has been mainly shown in studies with mice, it’s plausible that the same repeated exposure in people also causes the disease. Luckily the use of rotenone is now banned in the United States because of its health risks. Rotenone isn’t the only organic pesticide that can be harmful. At high concentrations, horticultural vinegar can be really dangerous to handle. Some insecticidal soap is labeled “Warning” or even “Danger” by the EPA because of its health risks, particularly when bare skin is exposed. It is important to note that the LABEL IS THE LAW. Read every pesticide label from front to back before you apply or purchase.

Organic pesticides are still designed to kill. Many homeowners turn to organic pesticides in the hopes that these products can cure their pest problem while protecting pollinators. The unfortunate news is that if it’s insecticide or fungicide it likely has some level of negative implications for our insect pollinator friends. Research pesticides BEFORE you purchase them — one useful tool is UC Davis’s Bee Precaution Rating database, where homeowners and licensed applicators can learn the level of risk to bee population of a given pesticide by trade name or active ingredient.

Even improper use of fertilizers can have bad environmental impacts. This is true for any pesticide or fertilizer, but the assumption that organic products are “safe” means that they are more likely to be misused. Repetitive, unnecessary or over applications of even a product like chicken manure — which is high in nitrogen and phosphorus — can cause an abundance of these nutrients in the water table, contributing to algal blooms, unhealthy stream systems or even earthworm poisoning. Test your soil before you apply nutrients in your landscape, and get help reading the results. There’s nothing “natural” about fertilizing plants, and it’s important to know if it’s even needed.

The Gist: Organic gardening practices are complex and worth carefully considering before we blindly adopt them. Many organic products offer a less toxic and more environmentally friendly alternative to conventional pesticides and fertilizers, but they can still have undesirable impacts! Every garden is a tiny ecosystem of beneficial microbes and insects, and what we do as gardeners not only impacts our health, but theirs.

Sierra Laverty is the assistant horticulture director at Idaho Botanical Garden, and is unapologetically obsessed with insects and plant diseases. She has worked in horticulture in the northern and southern hemispheres, but as a seventh generation Idahoan is immensely proud of Idaho landscapes. Laverty received a B.S. in Horticulture from Oregon State University.

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