Q:
I’m new to growing marijuana and I’m concerned about the safety of an organic liquid fertilizer I found here in Australia. The bottle states, “This product contains heavy metal impurities, it’s use may result in accumulation of cadmium in the soil”. Is this safe to use for growing cannabis plants?
A:
The short answer is that it is safe. Go ahead and uses it. The long answer is… long.
The labeling and packaging of fertilizer is highly regulated and these regulations often dictate what is printed on the bottle. In the United States, macro-nutrients are identified with only three numbers simply N-P-K. In Australia the regulatory agencies also require labeling to include sulfur N-P-K-S. Do Australian plants have a greater need for Sulfur? Absolutely not! This example is just one of many sometimes arbitrary regulations we growers have to wrap our heads around.
In the U.S. these regulations can vary from state to state creating big headaches for fertilizer producers. Though differences are usually minor, they must be carefully followed for the labels to be approved. In the U.S. there are no requirements to post heavy metal warnings but we don’t label foods with GMOs either so it shouldn’t be a big surprise.
High cadmium levels in agricultural soils do represent a potential public health concern. It’s not really that surprising that some governments require a warning about cadmium levels. If you would like to read more on the topic, here is a link to a PDF you might find interesting.
It’s entirely possible that your state and/or territory requires a warning level for all products containing detectable levels of cadmium but just about every fertilizer has some detectable levels of heavy metals. Actually many foods, cosmetics and water supplies also contain detectable levels of heavy metals. These cannot be entirely avoided but fear not, there is a difference between a detectable level and harmful levels.
If you look at the ingredients of this fertilizer, it’s made from ground up fish. Fish contain heavy metals. This is why sushi is not recommended for pregnant women. Most synthetically based fertilizers contain higher levels of heavy metals than organics, but they are still used in commercial food production around the world.
Cannabis growers like myself sleep better at night knowing that we’ve taken every step possible to keep cannabis clean and free from toxic materials. This is important but so is understanding the chemistry working behind the scenes.
Cadmium and Heavy Metals in Cannabis Fertilizer,
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