Pillar 01 · More than soil from a bag
The Substrate Library
More than soil from a bag. The Guild's reference shelf on growing media, with recipes you can actually mix. New entries the second Tuesday of every month.
What it is
Growing media, treated as a system
Each entry covers a single concept or recipe — the science and the practice in the same place. Foundation reading first, then the recipes that fix specific problems.
Who it's for
Growers who want recipes that hold
For people building a substrate practice that works across plant families, not chasing the next trendy mix. Apprentices start with the foundation entries; Growers and Educators reach for the recipes.
How it's written
Tested at the bench
Every recipe runs in the Guild's own collection — hundreds of plants, real failure modes, documented refresh windows. No claims without a cited source or a documented test.
Ten entries · Updated second Tuesday of each month
The reference shelf.
Foundation
Foundation
The Root Zone
What plants are actually asking for from substrate, and the three-ingredient recipe that fixes most struggling houseplants.
Going deeper
Going deeper
How Substrate Actually Works
Air-filled porosity, capillary water, perched water tables, CEC, pH, and the oxygen variable nobody measures. The physics underneath every potting decision.
Reference
Reference
The Aroid Ingredient Glossary
Pumice, perlite, zeolite, charcoal, coir, sphagnum, castings — every ingredient that goes in a chunky aroid mix, with the Guild's verdict on each. Including the ones we avoid.
Practice
Practice
Designing a Mix: The Logic Behind the Ratios
The framework behind every substrate recipe. How to work backward from what the plant needs and adapt any published mix for your own humidity, temperature, pot, and feeding style.
System
System Overview
The Petruscio Substrate System
Six recipes, three layers, zero bark. The map of which mix fits which use case — from root rot recovery to tissue culture acclimation to everyday aroid maintenance.
Daily-driver
Daily-Driver Recipe
Standard Mineral Mix v5
Sixty percent mineral, forty percent organic. The substrate most plants in the Guild's collection spend most of their lives in — the third leg of the system, after recovery and architecture for epiphytes.
Epiphyte
Specialist Recipe
Aroid Mineral Mix v5
Eighty percent mineral, twenty percent organic, zero bark. The mix built for climbing Philodendron, Monstera, Anthurium and the rest of the epiphyte rack — engineered around how aerial roots actually work.
Recovery
Recovery Recipe
ICU Mix v5
Seventy percent mineral, ten percent zeolite, zero bark. The recovery substrate the Guild reaches for when a plant arrives with black roots, plus the week-by-week protocol that gets it back.
Specialist
Specialist
Tissue Culture Acclimation
Substrate is a chassis, not a cure. What actually drives TC plantlet survival, and the mineral-based mixes the Guild uses across hundreds of acclimations.
Finale
Finale · Stewards-tier
Substrate at Scale: Why a Bag of Mix Is a Supply Chain
Every ingredient in a chunky aroid mix has a backstory. Tracing each one back to its origin (bog, beach, forest, volcano, mine) for Growers who think about how their bench connects upstream.
Buyer's Guide
Deep Dive · Buyer's Guide
Reading the Bag
Every bag of commercial potting mix is four decisions stacked together: base, aeration, charge, and biology. How to read them off any bag, plus a brand-by-brand look at FoxFarm, Espoma, Pro-Mix, Coast of Maine and more.