Technical Abstract: Byproducts of pyrolysis, known collectively as biochar, are becoming more common and readily available as ventures into alternative energy generation are explored. Little is known about how these materials affect greenhouse substrates. The objective of this research was to determine the effect of one form of biochar on the nutrient retention in a typical commercial greenhouse substrate. Glass columns filled with 85 : 15 sphagnum peat moss : perlite (v:v) and amended with 0, 1, 5, or 10% biochar were drenched with nutrient solution and leached to determine the impact of biochar on nutrient retention and leaching. Nitrate release curves were exponential and peaked lower, at later leaching events, and had higher residual nitrate release over time with increasing biochar amendment rate. Peak phosphate concentration decreased with increasing biochar amendment rate, while time of peak release, girth of the peak curve, and final residual phosphate release all increased with increasing biochar amendment. Potassium levels in substrates with 0% or 1% biochar increased linearly across leaching events, while substrates with 5% or 10% biochar exhibited an exponential release similar to nitrate and phosphate. Implications on greenhouse fertility management with regards to how biochar affects nitrate, phosphate, and potassium release are discussed.