Episode 171: Heavy Metals & Living Soil: How to Pass Compliance Testing with Greg Larson

How do you maintain a high-fertility organic living soil program in states with near-zero tolerance for heavy metals?

In this episode, Tad Hussey (KISS Organics) sits down with Greg Larson, a commercial cannabis consultant specializing in organic soil systems and heavy metal mitigation. Together, they break down the science and practical management of heavy metals in commercial cannabis cultivation, drawing on real-world data from facilities operating under tight compliance limits in South Dakota and Minnesota.

What You'll Learn in This Episode:

• Root Cause Testing: How to use ICP-MS lab testing to audit every facility input—from soil amendments and fertilizers down to irrigation lines and trim gloves.
• Input Selection Dynamics: Why ocean-based inputs (like fishbone meal) carry significantly higher heavy metal risks compared to land-based options (like bovine bone meal, feather meal, and soybean meal).
• Soil Chemistry & Plant Pathways: How maintaining optimal phosphorus levels and neutral pH prevents plants from absorbing arsenic through shared uptake mechanisms.
• Biomass Removal Strategies: Why pulling root balls instead of "chopping and dropping" removes accumulated heavy metals and systematically lowers soil contamination cycle after cycle.
• Beds vs. Containers: How larger soil volumes act as a buffer against heavy metal spikes while lowering labor costs and nitrogen requirements.
• Irrigation Fail Points: Managing reverse osmosis (RO) systems, preventing metal stripping from plumbing, and avoiding anaerobic soil pockets that increase arsenic bioavailability.

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