Is Galvanized Steel Harmful to the Soil

Could the bio-digester which is galvanized steel leach out zinc and be harmful to the garden soil?

In my last post I discussed a new method of worm composting mentioned on the internet. It is called a bio-digester and involves planting a small galvanized steel trash can with holes drilled into the soil about 3-6 inches. After I started to think about it I wondered if the chemicals from the steel would leach into the soil. Galvanized steel is made using zinc. I don’t want to put anything into my garden which could be harmful.  A few years ago I wanted to build raised beds using treated lumber.  I purchased the lumber and had it cut for the raised beds and then realized that the chemicals in the wood could leach out into the soil so I never used it.  If you are looking for an alternative to a galvanized steel planter you could click on this picture for a nice self-watering planter.

After researching on the internet I found a site called www.finishing.com and a forum discussing the poisonous aspects of galvanized steel.  Mostly there are questions from people who work with making galvanized steel but here and there I found questions about using it in the garden.  Since they are spaced throughout the page I copied the relevant questions and pasted them below.  If you click on the link above you can read through the whole forum:

May 28, 2009

Hi Ted! I have a question – I put galvanized fencing around my strawberry patch (to keep the birds out) and I’m wondering if that’s unsafe (could zinc leach into the soil, etc). In a previous post you stated that galvanized metal is not safe for food, but you also said that it’s okay for bath water. Thanks in advance for your response!

Catherine Chandler
– Orrville, Ohio

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May 29, 2009

Hi, Catherine. Galvanized fencing is fine. When we say it’s not food-safe we mean you should not cook in zinc pots or serve food out of zinc containers because of the possibility of acidic food or drink dissolving the zinc, and you consuming too much of it. Zinc is not poison; cold prevention tablets are one example of the deliberate consumption of zinc.

Regards,
Ted Mooney, P.E.
finishing.com
Brick, New Jersey

April 6, 2010

I would like to make balcony veggie garden boxes made from galvanized metal. These boxes will match the house.  Will the zinc leach into my soil and poison my vegetables?

Catherine Harley
– Boulder, Colorado
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April 6, 2010

Hi, Catherine. No, it won’t.

Regards,
Ted Mooney, P.E.
finishing.com
Brick, New Jersey

October 12, 2010
I see people using galvanized metal containers to grow vegetables. With water containing chlorides (salts), fertilizers containing salts, and eloctrolysis in the ground, I am wondering where the metals, etc are going when they dissolve. Is this not a hazard to eat food grown this way. Some even “line the galvanized container, but guarantee not to corrode for 8 years. So am I consuming heavy metals for 8 years until I replace the container?
Thanks

Alex Kallas
Sustainable agriculture educator – Vista, California, USA

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October 12, 2010

Hi, Alex. The MDR for zinc is 15 mg, and it is fairly common to take 100 mg per day for short periods to help ward off colds and flu. Although it is bad for welders to breathe zinc fumes, and it may be bad to put acidic foods into contact with zinc, zinc is not plutonium. Farm animals eat and drink out of galvanized troughs all the time, and in rural areas, people collect rainwater from galvanized roofs. It will take years for all of the galvanizing to dissolve into the soil, probably decades more for all of it to be taken up into the plants; then much of the plant will be thrown away or composted and only a fraction eaten.  I doubt that the vegetables have much chance of providing your MDR let alone deterring colds.

The term “heavy metals” is often used in an alarmist context, and it can be obfuscatory because it implies commonality between the dangers from tin, iron, gold and zinc on the one hand with cadmium, lead, and mercury on the other.

Regards,
Ted Mooney, P.E.
finishing.com
Brick, New Jersey

So it seems that it would be allright to bury the trash can as suggested in the online course.  So my next step would be to find proper drill bits to drill in metal.  One great thing about this trash can is the lid fits very tightly so that no wildlife can get into the compost for a nice dinner.

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10 thoughts on “Is Galvanized Steel Harmful to the Soil

  1. Pingback: Tweets that mention Is Galvanized Steel Harmful to the Soil | Gardening, Composting and Worm Composting -- Topsy.com

  2. Erika

    I wanted to know if I could edge my organic vegetable garden with brick instead of wood. Does brick leach toxins into the soil ?

    Thank you.

  3. donna

    I found some georgous zinc planters at Restaration Hardware. I want to plant my new improved meyer lemon trees in them. I saw in the catalog that it has a Propostition 65 warning. Which means it contains lead. Will this make it harmful to my lemons and would you be able to eat them?

  4. Sandie Anne Post author

    For myself, I don’t think I would want to use them. I would be afraid the lead would get into the soil. You can read more about Proposition 65 at this link.

    Sandie Anne

  5. Elizabeth DeMoss

    Is it safe to use rain water from a galvanized steel roof on a vegetable garden?

  6. Sandie Anne Post author

    Hi Elizabeth,

    I am copying this message from http://www.finishing.com/71/64.shtml.

    April 8, 2009
    Hi. My name is Shelley and I’m the mother of a 14 month-old. Currently, I do not have a bathtub, only a shower. I am wondering if galvanized steel is safe to use as a bathtub for my son. Will the zinc or other metal leach into the water where it may enter his mouth, eye, etc? Thanks!

    Shelley Desai
    hobbyist – Portland, Oregon

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    April 25, 2009
    Hi, Shelley. The feed troughs and watering troughs on many farms are galvanized; people in remote areas have collected rain water off their galvanized roofs for many purposes, including drinking, for decades; and a great deal of water piping (maybe most water piping) was galvanized until a few decades ago. I don’t think there is any danger at all, but if anyone thinks there is, they are encouraged to post the reason for their concern.

    Regards,

    Ted Mooney, P.E.
    finishing.com
    Brick, New Jersey

    Thanks,
    Sandie Anne

  7. Ginger Dunlap

    I used painted galvanized alluminum roofing to sheild against voles in my carrot bed. I wondered if it was a wise move, hence my search for an answer. From the questions asked & answered here, it puts my mind at ease to a certain extent. My ignorance brings me to ask if I’m referring to the same product, is the roofing steel or alluminum? Also, is roofing paint toxic?

  8. Sandie Anne Post author

    Hi Ginger,

    Maybe you could check with the place where you purchased the roofing and the paint to see if the roofing is steel or aluminum and if the paint is toxic.

    Best of luck!
    Sandie Anne

  9. Jim Blok

    Hi, i am very interested in worm farming.
    You mentioned, the galvanized container with lid.
    My worry is, that if you drill holes in the container, you probably can expect rust in the near future. My question is: is it not better to use a plastic, food grade material ?
    Poly propylene, polyethylene, etc etc.
    Please advise.
    Kind regards
    Jim Blok

  10. Sandie Anne Post author

    Hi Jim,

    For regular worm composting I would always use a plastic container not this galvanized steel trash can. I use Rubbermaid or Sterlite containers. It doesn’t have to be food grade. Here is more info on worm composting bins.

    I would only use the galvanized steel can as a bio-digester meaning digging a hole 6-8 inches deep and putting the can in the hole. And composting in the can. The attractive thing about this idea is that I could compost food scraps outside without any worry of any animal visitors getting into it, because it is made out of metal and has a tight fitting lid.

    Good Luck!
    Sandie Anne

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