since you asked: is copper sulfate a chemical?

Copyright National Pesticide Information CenterREADER DAVID wrote in to ask: “What do you consider a chemical? Is copper sulfate one?”

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.

Read about it.

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.)

  1. Mischelle says:

    I’m a Master Gardener and my favorite talk I give is on Integrated Pest Management. So often I hear people say, “I don’t want to use any chemicals in my garden.” My reply is, “Water is a chemical – do you plan to water your garden?” I then go on to tell them there are “safe” chemicals, and “not safe” chemicals and go further to explain that just because a chemical is naturally derived (as opposed to synthetic) doesn’t make it “safe”. Pyrethrins are just as deadly as many synthetic pesticides and should be used with caution.

    I am of the squish ’em or drown ’em camp. Slugs, Squash Vine Borers, and Japanese Beetles are my biggest problems and are usually easy to control mechanically, so I don’t bother with sprays. Proper plant spacing and good air circulation usually keep the fungi at bay.

  2. Marianne says:

    I love this answer. There are so many shortcomings in the current organic standards, and gardeners and farmers rely too much on external inputs to manage pests and disease. If I can’t manage a problem in my garden using other things in my garden (garlic, herbs, flowers and the insects that frequent them, my own two hands, etc.), it’s usually time to pull plants and plan better for next year. No two years are ever alike and if I’m not relying on any one crop for sustenance, who cares if I go a year without beans or have to press or process my goofy-looking apples rather than market them fresh. It’s better than contaminating my soil or deterring beneficials.

    1. c. hennes says:

      Marianne-If a farmer pulls up plants, how does she plan for next year without that source of income? I hope the conversation turns from what we shouldn’t do, to what we can do and still be a responsible steward. I have a large area I was hoping to turn into a market garden, but I simply don’t have the resources to pick and squash an endless supply of insects, try different disease cures that may or may not work, pull weeds, tend the nutritional and moisture needs of the plants, harvest, clean, transport and market. It’s difficult even to find time to research what needs to be done when a problem arises and there’s an abundance of conflicting advice, or it involves advice I don’t have the resources to utilize. At every turn I gain an understanding of how our systems evolved to the use of simple, cheap, labor saving methods, that guaranteed us a cheap food supply for many years, but tragically is not sustainable. This topic is so important, we have to keep trying to engage as many non-farmers as possible.

      1. Marianne says:

        If a farmer is planting only one crop then she’s not practicing sustainable agriculture to begin with. It’s true, there is so much to learn, and it is best learned by trial and error (mostly error). Plant your garden and tend to it as you can and you’ll learn along the way. I hope I didn’t imply in my previous response that farming or gardening is easy! It’s not. But neither require us to sicken the Earth or its inhabitants. Unless those inhabitants are the squash bugs taking up residence in my garden in which case THEY MUST DIE.

  3. Robert (Bob) Dudley says:

    Let me answer this question by simply stating that everything you, touch, eat or smell are made up of chemicals. Yes copper sulfate is a chemical, it occurs naturally as most chemicals do. Is is good for you. Well if you are an algae, or a fish it is not good for you. Copper is a micronutrient and we do need small amounts of sulfate. Too much copper can kill an idividual and there is a fair proportion of the population that is sensitive to sultafes. As I tell my friends all things in moderation. This holds true for natural or organic agricultural materials. Some of them can kill you faster than the agrochemicals from the big manufacturers.

    1. margaret says:

      Thanks, Bob, and welcome. An interesting reader question, right? Got me thinking, and reading — which I think is good for us (to study up, question…).

    2. Snuff curry says:

      Precisely. There are many readily available “natural” / non-synthetic chemical applications commonly used in agriculture and ornamental gardening that are far more dangerous to persons, places, and things than a pesticide applied properly, by a certified and licensed applicator, and according to its MSDS.

      1. margaret says:

        Thanks, Snuff Curry, for joining in. It so worries me that people buy products at the garden center labeled (organic” and think that means safe — as in no gloves, eye protection, etc. needed, and nothing to worry about. I fear we don’t read directions in general as a society, more ready, shoot, aim!

  4. Martin Connelly says:

    There is something a bit odd about this post. Of course Copper Sulphate is a chemical. You too, are made up of chemicals, as is everything you put on your garden. Neem is a chemical, etc etc. Water is a chemical. Some chemicals (like water) you cannot avoid putting on your garden, others (Copper Sulphate, for instance) you can. The choice is yours, but don’t go around saying “I dont put this on my garden because it is a chemical” since it makes you look silly.

    1. margaret says:

      Hi, Martin. That’s what interested me about the reader question. As gardeners, we probably use the word chemical (as in, “I don’t use chemicals”) to mean SYNTHETIC chemicals, such as glyphosate or industrially manufactured sources of Nitrogen. But the word doesn’t just mean that…nor are all naturally occurring chemicals safe.

  5. Todd says:

    My two cents on copper sulfate and bees – It is intended to stop fungi right? Well I recently learned that bees have fungi this live on the top of their head. When they pack pollen in the comb to store, they pack it in with their heads and some of that fungi transfers to the pollen. This fungi helps to ferment the pollen and make it more usable by the bees. Amazing isn’t it? The world of bees is fascinating. Anyway, when the bees encounter copper sulfate on say an apple bloom, it kills the fungi on the bees head compromising its ability to make food for itself. Magnify that by thousands of bees doing the same thing and you end up with a weak and eventually dead hive.

    1. margaret says:

      Well said, Todd, and thank you for one more insight into how “remedies” have more intricate impacts than we often understand.

  6. Keith Silva says:

    Copper-based sprays are often used to control peach leaf curl and other fungus diseases. Proper garden sanitation is an alternative that can go a long way in preventing such problems.

    The distinction between synthetic v natural, or chemical v natural is not important. What matters is the impact of our actions on the garden, environment, and ourselves. Copper is dangerous to all three.

    A good discussion regarding copper is here:


    Happy Spring!

  7. Chad Wohlers says:

    I AM a chemist, and copper sulfate is most emphatically a chemical. But, so is water and salt and sugar and lots of other things. So the question isn’t whether or not copper sulfate is a chemical, but whether or not it can be used in organic farming. These are two entirely separate questions. Please don’t use “chemical” as a pejorative term – it isn’t! I spent a good number of years trying to convince college students of that. After all, everything on earth, you and I included, is made up of chemicals.

    1. margaret says:

      Thanks, Chad. I agree — the acetic acid int he vinegar on my salad is a chemical, isn’t it? Delicious (in that concentration, at least)! And I agree that “chemical” is not a bad word — though when gardeners talk generically/imprecisely, sometimes it is used that way, to state that they practice organic gardening, as in saying, “I don’t use chemicals.”). So I was interested to read up (as in the story and links) about both sources of copper sulfate, and which ones are approved for organic use, and so on. Always so much to learn!

  8. Brooke says:

    I just checked my gardening supplies and yes, I have Bonide Copper Dust or Spray on my shelf. Although it was recommended for fungus/black spot on peonies I was always hesitant to use it, so it sits, full, on the shelf. How can I safely get rid of it?

  9. alan gorkin says:

    i went to a class given by a well known “organic” gardener. he had copper sulfate in a spray bottle and proceeded to show us how to spray it weekly on tomatoes to combat fungal issues. under the tomatoes were leafy greens. no gloves. i neglected to speak up…

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.