We’ve got a delightful little copper watering can in our garden, we’ve left it outside for too long though and it’s started to corrode in the rain. You have to run real quick from the faucet to the flowers or all the water drains out.
Although copper is good and indeed necessary for plants in small measures, too much can cause toxicity levels than can cause them to wilt and die. So copper watering cans are both bad and good for plants – and like most things in nature it’s all about getting the balance right.
If you’re thinking of buying an attractive copper watering can – or if you already have one – this article will help you assess the relative merits of both too much and too little copper for plants.
Signs of Copper Toxicity in Plants (& How It May Not Be Your Watering Can’s Fault)
It’s highly unlikely that a new copper watering can – or for that matter an old, corroded one – will release enough copper into the soil to be harmful to your plants.
Indeed, plants need a certain level of copper in the soil to thrive, so the chances of the trace levels (or lower) of copper in the water from your can making any difference to your plants one way of the other is negligible.
However, if you do see a turquoise color of corroding copper in the bottom of your watering can – and you use it very frequently and want to be more safe than sorry – then it could be time for an upgrade.
Old copper pipes in metal storage butts can also be prone to corrosion, so if you use a water butt in conjunction with your watering can – and both contain copper elements – then this may add to the copper levels in the water you use.
Many problems caused by copper toxicity – such as the yellowing leaves of iron chlorosis, or burnt leaf tips, plus stubby roots or just generally slow growth – can also be the result of other things, so double check to make sure copper corrosion really could be the issue.
For example, organic copper fungicides can actually be harmful to many young plants if not diluted sufficiently – so make sure you’re not doing anything else that could be introducing too much copper into the soil (if indeed it is copper that’s the issue).
Let’s not jump to blame our beloved watering can 🙂
How To Treat Copper Toxicity
If you’re convinced or at least pretty sure that copper toxicity in the soil could be an issue, then it’s best to try and leach it out with clean water.
This is easier in potted plants than in bedded ones, as you can simply run twice as much water as soil volume through the potted plants to completely cleanse the soil.
With bedded plants you can use a plastic watering can to the same effect, until you’ve thoroughly cleansed the soil for the next few waters – before perhaps returning to a new replacement copper watering can again afterwards.
Did I say plastic watering can? Don’t get me started on plastic micro particles! That could be the subject of another article.
Copper Deficiency in Plants
A more likely scenario to your copper watering can making your soil toxic, is that your soil and plants are in fact suffering from copper deficiency.
Plants need copper to grow, and most have an average of 15 parts per million (ppm) in them, whilst soils can range vastly between virtually none and over one hundred ppm.
Far from worrying that your copper watering can is adding too much toxicity, it’s actually essential that your soil has enough copper present for your plants to flourish.
The hard part in all this, is that the effects of copper deficiency in your plants may look very similar to copper toxicity – namely leaf edges that look frost-bitten and/or black and dark blue. Your plants can also just die off. So determining cause is key here.
In general, copper deficiency in soil and plants is caused by either too much organic material such as mulching on top of the soil, or too much alkalinity or acidity within it.
When used as a mulch, non-decomposed organic material like leaves or grass cuttings can starve the soil of copper and other minerals until the decomposition process starts and these minerals start leaching down through the soil.
Whereas strongly acidic soils such as peat heavy ones, or soils with a high PH level that are very alkaline – can all suffer from a deficiency of copper.
How To Treat Copper Deficiency
Depending on the type of plants you’re growing and the square footage of soil, organic copper fungicides can help in moderation to treat copper deficiency. But again, this is all a balance as you don’t want to overdo it and create a toxicity problem.
Copper sulphate and oxide fertilisers can be used at a mix of around five pounds per acre to add copper to your soil, and can simply be dug in and turned over to broadcast the minerals around the area you are treating.
Such copper based fertilisers can also be sprayed on to the leaves of your plants, although this is much more time consuming if the area you’re covering is large.
Whatever method you choose to employ, it’s important to read the manufacturer’s guidelines on how to use the product first, and always take into account the type of ground you’re covering and the range of plants you grow and are wanting to treat.
Not all species of plant will respond well to the introduction of copper based fungicides – whether organic or artificial – so it pays to take your time and do your research before committing to a large scale treatment program. Take professional advice if you’re at all concerned.
Is Copper Good or Bad For Plants?
While it’s good to know that our humble little old copper watering can is likely not poisoning our plants – it’s also a bit daunting to discover the whole issue of soil and plant copper levels is so complex.
It turns out there’s a fine balancing act to be carried out between suffering from either too much copper in your soil – or too little, and there are a variety of factors which influence both.
However, through clean water leaching and with the introduction of copper based fertilisers, it would seem that we have a solution at hand for both these problems.
So by all means replace your copper watering can if that tell-tale bluish-green color associated with corrosion starts to show itself – but otherwise you can keep using your trusty can with confidence.
Homeowner and property investor Larry Jones founded Take a Yard in 2020 to bring you the very best outdoor living content, based on his years of experience managing outside spaces. Read more >