The objective was to quantify the extractable micronutrient levels from container substrate components and limestone and their potential contribution as fertilizer sources for crop growth. Samples of horticultural limestone (29 samples) and substrate components [peat (48 samples), perlite (10), vermiculite (14), bark (15), and coconut coir (6)] were analyzed for micronutrient content with the SME (Saturated Medium Extract) method using either water (SMEW) or diethylenetriamine pentaacetate (SMED) as extractants for the substrate components, or following acid digestion of limestone samples. Samples were obtained from commercial substrate and greenhouse companies throughout the U.S. and Canada. Peat included 36 peat samples from two peat bogs in Alberta Canada to evaluate whether species composition, decomposition, and bog location affected micronutrient content. Increasing von Post decomposition increased SMEW and SMED Mn level and SMED Zn. As percent Sphagnum fuscum increased, extractable Fe and Mn levels increased for both extractant types, and SMEW extractable Zn increased. Based on established SME guidelines for acceptable to optimum nutrient levels for soilless substrates, peat and bark could potentially provide sufficient Fe and Mn to contribute to plant requirements. Average Fe content in limestone was 0.11%, and Mn content was 0.012%. Based on SMED extractions and lime analysis, Fe supplied by 100% peat and lime could potentially provide Fe at levels comparable with commercial pre-plant fertilizers if these Fe sources are plant-available. Substrate-pH affected solubility of Fe, Mn and Zn in peat. As substrate-pH increased, Fe and Zn solubility in peat decreased with both SMEW and SMED. The SMEW-extractable Mn decreased with increasing pH, in contrast to SMED-extractable Mn which increased as pH increased. Analysis of raw materials using SMED (substrate components) or complete digestion (limestone) is advised for substrate companies to proactively identify batches of components that may affect crop nutrition. Given this high level of potential contribution of Fe by peat and lime, it is likely that these uncontrolled sources contribute to nutrient uptake in horticultural production. However, further research is required to compare extractable micronutrients with actual plant uptake.