since you asked: is copper sulfate a chemical?
new feature: ‘since you asked’
I SPEND MANY HOURS each week trying to answer reader questions, which arrive in email and comments in such large numbers that I cannot keep up, I am sorry to admit. But I do manage to answer some, which led to this thought:
Why keep the replies hidden, between me and the individual questioner, I figure, so here we go: a new feature called “Since You Asked” that shines a light on the “best” questions—which might mean most practical, or most timely, or simply the oddest one that appealed to me who knows why.
I’ll “tag” all the entries at this link to make a stockpile of them for future reference; this is the second one.
SO IS COPPER SULFATE a chemical? I am not a chemist, but a gardener, so here is what I know with help from more expert sources:
Pure copper sulfate is an inorganic compound that does occur naturally, but is more commonly man-made from natural components–copper and sulfur. With restrictions, some products containing it are allowed in certified organic agriculture.
Note that I’m not using the -organic part of the word inorganic as in “labeled for organic use.” By inorganic I mean that it does not derive from living or formerly living material (like plant-based rotenone, or azadirachta, the insecticide derived from neem, do). Instead, copper sulfate is of mineral origin–from a geological system, not a biological one.
The compound is found in products with a wide variety of intended applications, including as a fungicide, algaecide, molluscicide, root killer, antimicrobial, and antibacterial. Products containing copper sulfate vary widely in formulation, and the “signal words” on their labels reflect that, ranging from Caution to Danger (get a pdf explaining signal words). Not all are approved for organic use.
Despite being natural, rather than synthetic, copper is dangerous if allowed to build up in the soil, and dangerous to inhale, or get on your skin. It is also somewhat toxic for birds and highly to very highly toxic for aquatic life. There are no registered indoor uses for copper sulfate, says the National Pesticide Information Center.
Because a chemical compound contains natural ingredients doesn’t mean it’s safe–as expert Jeff Gillman agrees (remember?). Many organic farmers and organic gardeners, including me, don’t use these substances, or use them only as a last resort. I asked Jeff, author of “The Truth About Organic Gardening” and one of the popular Garden Professors blog contributors on Extension.org, for more detail.
“Copper formulations are usually allowed for organic production, but these compounds can be very damaging to the environment, and they don’t break down,” he said. “Worms, for example, can be seriously affected by high levels of copper in the soil, as can microorganisms.
“One or two copper applications won’t make your garden a sterile wasteland, but this is definitely a pesticide you want to apply as infrequently as possible.”
the manufacture of copper sulfate
As mentioned, copper sulfate occurs naturally–but most of what’s used today is manufactured, not mined.
“The Romans found it in solution in copper mines, calling it chalcanthus,” says this great, short podcast (and transcript) from “Chemistry World” magazine of the Royal Society of Chemistry in the U.K. “Copper sulfate does crop up as a solid in nature, often crystallised on the walls of mines and caverns. However this isn’t a substance that there is any need to mine. It is easy enough to make by reacting more common copper compounds like copper oxide with sulfuric acid.”
The Copper Development Association Inc., a trade information entity, reports that more than 100 manufacturers worldwide produce copper sulfate, with the world’s annual consumption around 200,000 tons. The Association estimates that approximately three-quarters is used in agriculture, principally as a fungicide, but lists its numerous other applications here.
my bottom line
MY BOTTOM LINE (since that’s what reader David asked me for): Copper sulfate is a chemical compound, but not one made from synthetic ingredients. “Synthetic” is what most people mean when they use the word “chemical.”
I don’t use synthetic chemicals, but I also almost never use “natural” ones, either, because of concern for residual effects they may have on soil, water, or animals (including pollinators and other beneficial insects, and including me). Some are too broad-spectrum for my comfort zone, killing not just a desired pest, but perhaps beneficials, too, for instance. Many mineral- or plant-based chemicals–the natural ones, including that rotenone I mentioned up top–just don’t feel safe enough to me.
What’s your bottom line on what’s a chemical, and what you feel comfortable using in your garden?
(Image copyright National Pesticide Information Center, a project of Oregon Statue University and the U.S. Environmental Protection Agency. Disclosure: Books purchased from Amazon affiliate links yield a small commission.)