Mold on Unglazed Ceramic Pots: Porosity Problem

A Rhode Island ceramist made highly absorbent, unglazed red Mino clay pots without drainage holes. Hyacinth bulbs in Scott's potting soil developed green/white surface mold within three weeks despite daily light watering.

Root Cause

The clay's extreme porosity wicks water and dissolved organics/fertilizer to the exterior, where they feed mold. No glaze = inevitable surface mold.

Solutions

• Glaze the interior (at least) to stop wicking.
• Use less porous clay for future pots.
• Add drainage holes—essential for plant health.

Unglazed, hole-less pots are unsuitable for horticulture; they create a perpetual mold farm on the outside and waterlogged roots inside.