We drink a lot of coffee in our house so we have tons of these aluminum (?) cans (about 10cm in diameter):

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I would like to re-purpose these cans as growing containers for some hot peppers (Capsicum X). I can imagine any acids in the soil can dissolve the metal of the can, despite it probably having some inner coating. Is it safe to eat fruits harvested from a plant that grew in a metal container?

  • The bottom seam makes it almost certain to be a steel can ( ferro- magnetic) , no doubt with an organic coating. As nearly every soil has significant amounts of iron , I can't imagine how it could be unsafe. – blacksmith37 Feb 18 '19 at 21:10

I can't tell how tall and wide the can is, there's nothing to give reference for scale, so its possible the can is not of an appropriate size to grow a reasonably sized plant. However, given you don't really know what it's made of, I wouldn't recommend using the cans for edible plants; there may be tin in the mix of materials used to make the can, and that can be absorbed by plants. Even if the interior is coated with something safe for foodstuffs, you will, of necessity, be damaging that when you drill holes in the bottom for drainage.

There is another drawback with metal containers in that they provide absolutely no insulation, allowing cold and heat to penetrate the soil inside (and the roots of your plant) freely. If you want to try growing ornamental plants in them, that's fine but the caveat re insulation still applies. https://www.hunker.com/13427185/can-you-grow-plants-in-tin-containers

  • I would just add that the best-by dates are not only for the food, but also for the container. Containers (so cans, bottles, etc.) will lose dangerous stuffs that will accumulate inside [and this is the reason salt, water, and other "unexpirable stuffs" have a best-by date. On the other hand, we do not eat many chili peppers (and very "diluted" on our meals). – Giacomo Catenazzi Jan 31 '19 at 12:40
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    "Best by" dates are just a legalized scam by the food industry and supermarkets to make gullible people throw away perfectly good food and spend more money to replace it. The only labels that matter for food safety are the ones that say "use before", not "best before". – alephzero Jan 31 '19 at 12:48

If you know that aluminum is your only concern, I wouldn't be too worried about whether your plants would be toxic to eat. Soil in and of itself is already high in aluminum. So, plants are probably pretty good at absorbing only amounts that are needed. However, the form of aluminum may make a difference there. So, it's hard to say for sure.

Now if you were asking whether growing rice in soils high in mercury and arsenic is a good idea, I would give you a resounding no (unless your purpose is to accumulate the metals to help purify the soil and then toss the rice). Some plants do accumulate some metals. It's different for different kinds of plants.

So, I imagine what you're actually growing in these cans makes a big difference as to whether it's safe for you to eat the resulting plants. I don't know about peppers there.

Cans are often lined on the entire inside (not just the lid or some such) with BPA (or a similar chemical), which is a xenoestrogen. And while BPA isn't exactly good for you, this is to prevent too much of the metals from leaching into the can and/or corroding. I don't know that plants accumulate BPA in their fruits, but I have my doubts. The chemicals might affect the plant growth and/or behavior, however. They also put BPA in soda cans (which are full of carbonic acid; I understand that plant roots also produce acids; so, I don't know that they would remove the BPA). Bacteria/fungi in the soil might degrade the BPA faster than the plants, however.

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