My question is about the ceramic pots that you see in nurseries and
places in the area. The pots are glazed on the outside, and unglazed on
the inside, and they are made in China and Vietnam. Are these pots safe for planting vegetables and herbs? Or, are there materials in the interiors of the pots that could leach into the soil and make the vegetables and herbs unsafe to eat?
Some ceramic glazes do contain toxic materials, such as lead and cadmium.
Washington State Department of Health has information on preventing lead poisoning, and on testing for lead.
State of Oregon’s Lead Poisoning Prevention Program includes information on sources of lead exposure, including pottery.
California Department of Health has several pages on toxins in pottery.
Excerpt:
“The U.S. Food and Drug Administration (FDA) sets standards at the
national level for the amount of lead that can pass out of, or ‘leach,’
from dishes. Tableware with lead levels greater than these standards
cannot legally be sold in the U.S. The FDA regulations cover only
tableware that is imported or that is brought into the state for sale.
The standards apply only to items that are used for foods and beverages.
They do not apply to pieces that either cannot hold liquids or are not
intended to hold liquids, such as salt shakers, cookie jars, butter
dishes, etc. See the table below for the FDA standards for lead in
ceramicware.
Decorative ceramics
The FDA has labeling rules for ornamental or decorative ceramics that are
not intended for food use. These items must either (1) be permanently
labeled with a logo or statement that they are unsuitable for food use,
or (2) be made incapable of holding liquid. If an item is clearly
intended for food use, such as a bean pot, labeling it is not sufficient,
however. It must be made unusable, for example, by having a hole drilled
through any surface that could hold liquid.”
My co-worker tells me that some retail stores are good about informing customers if pots are unsafe for food use. This
document from Clemson University Extension (although its focus is
cookware) suggests that you not use pottery which does not bear the
label, “Safe for Food Use:”
If a pot has been fired at a high temperature (something you cannot
easily ascertain by looking at it), my thought would be that there would
be less likelihood of toxic material from the glaze leaching inward, but
if the clay itself comes from a source which is full of contaminants,
there may be a risk apart from the glaze. If you are at all concerned
about using these pots for growing food, my advice would be not to do it.
There are other ways of growing food in containers, such as untreated
wood boxes or barrels. See links here for general information on growing
vegetables in containers:
Vegetable Gardening in Containers from Virginia Cooperative Extension.
Plants Grown in Containers from North Carolina State University.