Overwatering on sedum
What's Happening
Standard potting soil contains 60-80% peat moss and fine organic particles that compact within 2-3 months of watering. Compaction reduces pore space (macroporosity) below 15%, creating anaerobic zones even when surface soil appears dry. Succulent roots require 30-40% macroporosity for oxygen exchange above 2mg/L threshold. Fine particles also retain capillary water that wicks upward, maintaining root zone moisture for 7-14 days beyond what succulents tolerate. Inorganic amendments (perlite, pumice) create permanent pore spaces that resist compaction and allow gravitational drainage.
How to Fix It
- 1
Base component: 40-50% high-quality cactus/succulent soil (provides organic matter and nutrients)
- 2
Drainage amendment: 30-40% perlite or pumice (creates air pockets; perlite floats, pumice sinks—both effective)
- 3
Structural component: 10-20% coarse sand or fine gravel (maintains soil structure, prevents long-term settling)
- 4
Particle size test: Individual components should be 3-6mm diameter; dust and fine particles removed by sieving
- 5
Drainage verification: Water should exit drainage holes within 30 seconds of pouring; if pooling occurs, add more inorganic amendment
- 6
Container pairing: Use unglazed terracotta with gritty mix—combined evaporation through pot walls + gravitational drainage creates ideal moisture curve
What You'll Need
How to Prevent It
Refresh soil mix every 12-18 months as organic components break down into moisture-retentive mush. Never use standard houseplant potting mix for succulents—even with 'added perlite' from manufacturers.