Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Galvanized steel for planting vegetables
Q. Is galvanized steel safe to use as tomato planters? I am worried about leaching of metals into the vegetables.
Barbara Meservehobbyist - Fallston, Maryland
2007
A. Zinc is an essential dietary element.
It is extremely unlikely that any will end up in the tomato but if it does you can put the price up.
Geoff Smith
Hampshire, England
A. Galvanized steel is commonly used for tomato plant towers. Don't process the fruit in galvanized (or bare steel) containers though, as the acidity will dissolve some metal.
Ken Vlach [deceased]- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
Q. I bought some large galvanized planters with no drainage holes (for indoor or outdoor use). Since they are square, I am having a hard time finding liners that allow me to maximize the space. I would like to plant some herbs and small tomato plants in them. If I drill holes in the bottom and plant directly in the steel, would the planters be considered food safe for planting?
Linda Gatesconsumer - Bethesda, Maryland
May 27, 2009
Q. I use galvanized screen and fencing around my garden. It is buried in the soil, around the plants, to support vines. I also allow my vegetables to sun and dry on a galvanized screen tray. Are there any human health problems associated with vegetables or roots coming in contact with galvanized screen wire? Thanks.
Lance Laton- Atlanta, Georgia
June 17, 2009
A. Hi, Linda. The earth is largely iron, and zinc is an essential nutrient. There is no safety issue with your plan but, placed in the ground, the planter may rust away to nothing sooner than you expect.
A. Hi, Lance. We added your question to this thread which probably answers it for you. It is safe.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I'd like to grow an herb garden outside my kitchen door. Crate and Barrel has a "Wide-rimmed planter in lightweight, zinc-finished galvanized steel" with an over-the-railing plant holder that fits over my aluminum railing - very convenient to run out the back door and grab what I need while cooking. And the plants wouldn't take up space on the very tiny patio.
Is there any reason to think that this zinc-finish on galvanized steel could leach toxins into the soil, and then into the herbs? The planter is made in Vietnam. I am somewhat leery of the safety of food related items imported from China or outside the US. If there is the slightest chance of toxicity, I won't use it.
gardener - Westfield, New Jersey, USA
May 7, 2012
A. Hi Mary.
We appended your inquiry to a similar thread which should help reassure you. On top of that, your planter is sold as a planter, i.e., it is designed for the purpose, which should offer some indeterminate extra amount of assurance compared to using something that wasn't designed for the purpose.
But with cadmium in children's jewelry sold in Wal-Mart, lead in the paint of kids' drinking glasses given away at McDonalds, antifreeze in the dog food ... requiring "not the slightest chance of toxicity" is asking a lot. But I think we can very safely say that growing your own herbs & spices in that planter will be far safer than using imported herbs :-)
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I have read a lot of answers regarding the safety of galvanized aluminum planters. My question is, what about galvanized aluminum sheets? I saw a raised garden bed on Pinterest made from a wooden frame but on the sides they used galvanized roofing material.
Would that be just as safe as planters made from galvanized aluminum? I have the same concern that over time the zinc or other metals would leach into the soil. However this would be for a flower garden and not vegetable garden, but the planter would make a nice raised vegetable garden as well...
- Manchester, Connecticut
May 17, 2013
A. Hi Roger. There is no such thing as galvanized aluminum. Such sheets are either made of aluminum or they are made of galvanized steel (dipped into molten zinc).
This is just an opinion-based public forum. I don't expect that any epidemiologist will conduct a proper double-blind longterm study of vegetables grown in galvanized planters vs. vegetables grown in other containers. But again, zinc is an essential nutrient, not a toxin. And if you are not doing a soil analysis of the dirt that you are planting the vegetables in anyway, nor the wood that the frame is made of, nor the fertilizers/plant foods you may be adding, trying to estimate whether there may be a slightly higher zinc level in the soil as a result of using a galvanized planter box is focusing on the inconsequential. I'd say concentrate on any insecticide or herbicide use. Good luck!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Hello, I have recently bought some large old galvanised drinking troughs. The idea I have is to fill them with soil and plant them up with edible fruits and vegetables. Should I be concerned about the cadmium and zinc leaking out into the vegetables? I have noticed that the bottom of the inside of these troughs is showing signs of rust so should I be concerned that the coating is breaking down and leaching into the ground also? Is it best to use some sort of liner and what sort do you suggest is the safest to use? Thanking you in advance for your advice. Regards David
david lee- salisbury wiltshire England
June 24, 2013
A. Hi David. There will be no cadmium is a drinking trough, and the zinc is an essential nutrient.
You may need to be concerned about their durability if they are already rusting though -- so you may want to paint them. But no worries about toxicity. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I am trying to find out if there are any long-term issues with growing edible plants in galvanized steel stock tanks or garbage cans. Does galvanization only use zinc in the coating (in which case I don't have much concern) or does galvanization also involve other "heavy" metals, like cadmium? I understand that after several years, the coating will begin to flake off, so I am concerned about uptake into the plants, and hence into the edible parts of the plants. I want to plant in large metal containers to confine the spread of the plants, so it is for long-term perennial use.
Can you compare if pre-galvanized steel or post-galvanized steel would be better for this purpose?
- Norwich, New York, USA
June 26, 2013
A. Hi. Galvanizing does not use cadmium. There may be small amounts of lead or chrome in galvanizing, or even cadmium, but everything is relative, and galvanized containers will be safe to plant in. Post-galvanized coatings are heavier and therefore longer lasting.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Galvanized Sheet and Composting Rack
Q. Dear Sirs, I am interested in building an above-ground composting rack. One component will be corrugated galvanized sheet metal. Eventually this material will rust. In your best available opinion will the leaching metals be concentrated enough to be harmful. I know that is a broad question, but simply looking for some general guidance. Thanks in advance for your help. Scott
Scott Steinbach- Waco, Texas
April 22, 2016
A. Hi Scott. No.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I saw an ad for a space saver strawberry garden. It is made of 3 stacked rings made of corrugated aluminum bands. Is it safe to plant vegetables in aluminum containers?
Linda GriffithsHome gardener - NORTON, Ohio United States of America
March 2, 2018
A. Hi Linda. There may already be more aluminum in the soil in your strawberry garden than could dissolve from those bands in a lifetime. Aluminum is the 3rd most abundant element on earth -- over 8% of the earth's crust.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
March 2018
Thank you very much for answering my question
Home gardener - NORTON,Ohio United States of America
Q. Hi! I am planning on using galvanized mesh cloth to line my raised beds. It is steel galvanized post-weld.
Should I be concerned at all about metals leeching into my soil over time? I understand that acidic soil may leach the zinc. Would it be able to leach toxic levels? And I'm worried that the weld is lead based. Is that a possibility? And if so, does the galvanization process seal it in? Would I need to be worried about lead leaching over time as the galvanization degrades?
Or I guess, what would be your suggestion of what to look for in gardening mesh that will be underground to control gophers in a veggie garden.
Thank you!
- Atlanta, Georgia USA
April 10, 2018
A. Hi Jenny. I don't really understand your question about lead-based welds. To my knowledge steel is welded with steel welding rod.
What I would look for is any product designed for the purpose. The chance of you being harmed by it then is quite small; it is when we re-use things that were designed for other purposes that we must worry about what they might be made of. But even galvanized wire cloth may not last more than a couple of seasons underground.
(patience please, link is now broken, and document must be retrieved from the billions of such at archive.org)
The zinc "leaching" question has already been answered many times already on this page; but if you're not confident about these opinions you can obtain white papers on the subject ⇨
Luck and Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Hi there,
Instead of using hardware mesh on the floor of my raised bed to keep out voles I want to use painted aluminum soffits with holes. I believe they will last much longer than galvanized hardware mesh. These soffits (2-3) feet are at many construction sites I have seen, and are for the junk yard.
Is there any issues with the aluminum or the paint poisoning the soil?
- rossland, bc, Canada
August 29, 2018
A. Hi Frank. Aluminum per se is probably not dangerous to plants, as so much of the earth is aluminum. However, soluble (dissolved) aluminum is more problematic and quick googling reveals that it can be a serious strain on the plants if the pH is under 5.
Hundreds of papers have been written about the subject of aluminum take-up by plants, and I've spent no time with them, so I suggest that you invest an hour or so in research on the topic before committing to this plan.
Paints are of many different types so it's hard to say what is dangerous in the soil. Some consumers would be leery of, for example, the fluorinated paints that are commonly used on industrial and commercial buildings.
My personal philosophy is that you're usually (not always, of course) safer with something designed for the purpose than with something designed for another purpose because then you never know what the designer was thinking. Just as a thought experiment, although it's very unlikely, suppose the soffit designer had decided he'd try to address the problem of squirrel nests in people's homes by putting poison in the paint?
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Lead leaching from galvanised steel raised bed?
Q. Hi,
Need to build a raised bed because I've discovered our soil has ~150 ppm lead.
Thought about using Galvanised Corrugated Steel, like this:
Now I've learned that Galvanised Steel may also contain lead.
A lead test kit
[lead test kits on
eBay
or
Amazon [affil links]
on the panels I bought eventually turns a very dark red. No pink.
Another brand swab is negative.
How much lead is likely to leach from these panels into the soil?
Thanks!
Tom
- San Pedro, California, USA
June 27, 2020
A. Hi Tom
It is extremely unlikely that any lead in a galvanised sheet could migrate into soil and then into plants which take up very little lead anyway.
But before you rush ahead it would be worth reading https://www.soils.org/about-soils/contaminants/lead
I should also point out that getting a representative sample of soil is not simple. You need a large number of samples from all over the plot from a reasonable depth Mix them thoroughly (not easy) and then halve the sample, halve that and so on until you have a small enough sample to test. Otherwise you might take a single surface sample with one flake of old paint and draw wrong conclusions.
Geoff Smith
Hampshire, England
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