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Copper fertilisers do not exist!

Ok, so that title, on the face of it, sounds ridiculous. And yes, you can buy ‘copper fertilisers’ and people use copper fertilisers. However, I hope to convince you that only do they not exist, but that you should not be using products that purport to be copper fertilisers.

So let’s look at the first part; do they exist? Well, you can buy liquid and powdered copper products to apply to plants, I do not dispute this. However, I have the following issues with them being classified as fertilisers:

  1. No plant is ever deficient in copper. Soils are always stocked with ample levels of this micronutrient. Copper is a micronutrient, so only required in minuscule quantities by plants. This requirement is more than met by even the most nutrient deficient soil. Some would argue that it is the ‘availability’ that is of concern. But even in the most extreme soil pH there will be enough copper to meet a plant’s nutritional requirement. When I state this to farmers I invariably get the follow up question ‘but when copper is applied to my crop, I always see a yield up lift, explain this!’ And this leads me to my second point:
  2. Copper fertilisers are pesticides in disguise. When you apply a copper fertiliser, the high level of soluble copper acts as a powerful microbial sterilising agent. It will kill microbial life indiscriminately. As such, it is acting as a pesticide, even if you didn’t intend it to. Now your crop may not have been showing any sign of disease, but that is not to say that it isn’t there. In fact if you run a leaf sample of wheat through analysis late in the season you will pick up the DNA of powdery mildew regardless of whether the plant is showing symptoms of this disease or not. So applying copper to otherwise seemingly healthy crop can still have a pesticidal activity. What would convince me to change my mind? Perhaps a study showing copper improved the growth of a crop plant growing in complete aseptic conditions in a healthy normal soil.

While some growers may be unaware of copper’s antimicrobial activity, others are very aware, and are using copper to bypass pesticide regulations. This is one of my major bugbears. It is not about gaming the system or bending the rules. Copper is a very toxic substance. Copper is a heavy metal that builds up in the human body and causes serious health issues. Copper is residual in the soil and will have a long-term impact on soil health and the wider environment. 

In many cases these copper products are being used to control diseases on trees and shrubs which involves applying huge volumes of copper into the environment. The suppliers/manufacturers know this and complicit in this environmental vandalism. And we are not just talking small cowboy companies here. Since Bordeaux Mixture had its authorisation revoked for safety reasons, even some very large companies have remarked their bottles as ‘copper mixture’ fertilisers but still with the same markings and branding as their old pesticides. They also use Google Ads and Amazon search optimisation to point customers searching for Bordeaux Mixture to their new copper fertiliser.

Cherry trees in spring treated with copper. This copper will dissolve in rainwater and contaminate the soil and water course.

I think a major part of the acceptance of copper products in agriculture and horticulture is due to copper being perceived as innocuous and bland. We associate copper with pipes and wires, not with the toxic effects of its soluble salts.

For these reasons, at Eutrema we never advise the use of copper fertilisers or pesticides. We also believe that copper fertilisers should be banned. Furthermore, we think it is a ridiculous situation that copper should be allowed to be used in organic farming, which should have the highest food and environmental safety standards. Give me an apple sprayed with a regulated, tested, and biodegradable conventional pesticide any day over one sprayed with copper (although I would prefer one sprayed with an alternative bio-pesticide of course!).

So please do not buy or use copper fertilisers. You do not need them, and if you think you do, consider a far safer bio-pesticide or fertiliser; examples include Eutrema’s Chitosan, Salicylic Acid, Sea Silica, and Lime Sulphur. But even if you do not buy our products, we’ll be happy as long as you don’t choose a copper-based product.

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