Galvanized Container Gardening #170051

Asked March 13, 2014, 5:53 PM EDT

I would like to start container gardening.  Is it safe to grow fruit and vegetables for human consumption in galvanized water troughs?  Specifically, will the zinc and/or cadmium from the galvanizing process leach into the soil and plants?  Would plastic or fiberglass troughs be safer?

Brazos County Texas

Expert Response

I have looked at Extension internet sites for information regarding the safety of eating food grown in galvanized containers, and find little specific information, but in what I find, there is varying opinions, but no research based outcomes.  So, I cannot definitely answer your question at this time.  For your consideration: As you may know, galvanized containers have a zinc coating (which can contain cadmium).  The coating protects the underlying metal (steel or iron).  Over time, the coating corrodes and the zinc and cadmium are released. Zinc and cadmium are dangerous to humans if consumed in high enough amounts  (however, small amounts of zinc are considered an essential micronutrient for both plants and humans). Here are a few points to consider regarding the safety of growing edibles inside galvanized containers:
  • the biggest danger cited with respect to galvanized materials in contact with food is to not cook or serve food or drink inside a galvanized container (because of the possibility that the acidity of the food or drink will dissolve the zinc, thus leaching it into the food or drink)
  • another big danger cited with respect to galvanized metal is that it is dangerous to breathe the fumes created when heating the metal (such as during welding)
  • humans in rural areas have collected rainwater (for drinking water) off of galvanized roofing for many years
  • residential water was supplied in galvanized pipes (and still is in some areas) for many years
  • livestock and pets have used galvanized containers to drink water out of for many years
  • if the plants in your galvanized container absorb the zinc and cadmium, it will most likely be in very small amounts and the plants themselves will show toxicity if the amounts are too large
  • a plastic liner could be used inside the galvanized container to minimize soil contact
  • older galvanized containers that are rusting would be much more dangerous than newer ones

An Ask Extension Expert Replied March 17, 2014, 4:57 PM EDT

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