A plant-derived natural foaming compound (found in Saponaria and other plants) used as an organic wetting agent. When stirred into water it creates foam that helps spread moisture evenly through peat-based soil mixes.
Jeremy reaches for saponin when one of the 10-gallon pots is so dry that water runs straight through — the saponin breaks the tension and he gets full saturation with no runoff.
Discussed in: Ep 002 · Ep 003 · Ep 004 · Ep 018 · Ep 020 · Ep 021 · Ep 030