Episode 171: Heavy Metals & Living Soil: How to Pass Compliance Testing with Greg Larson
Cannabis Cultivation and Science PodcastShow Notes
In this episode of the Cannabis Cultivation and Science Podcast, host Tad Hussey catches up with commercial cannabis consultant Greg Larson to tackle one of the most pressing challenges facing organic growers today: passing strict heavy metal compliance testing in tightly regulated states like South Dakota, Minnesota, and Maine.
Tad leads a deep-dive discussion into Greg's hands-on work reducing heavy metals—specifically arsenic, lead, and cadmium—in commercial living soil operations. They explore how Greg and his team systematically isolated contamination sources through precise ICP-MS testing (down to parts per billion), evaluating everything from soil formulations and fertilizer inputs to trim gloves and RO water systems.
The conversation breaks down critical soil chemistry strategies for suppressing heavy metal uptake, including keeping soil pH near neutral and maintaining proper phosphorus levels to prevent plants from absorbing arsenic through shared biological pathways. Greg highlights the practical differences between land-based vs. ocean-based inputs, the cumulative nature of heavy metals, and why removing root biomass after every cycle is essential to progressively lowering heavy metal thresholds over time. They also compare the performance, labor demands, and heavy metal dynamics of growing in living soil beds versus small containers, offering actionable advice for commercial cultivators navigating strict state regulations.
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