Bagged mix is a mystery bag: you don't know what's in it, and the biology is usually dead on arrival. This builder fixes that. Pick your goal, get a castings-centered recipe, and scale it to whatever batch size you need.
Why castings in every mix? They bring living biology, gentle nutrition, and moisture-holding humus — with a low burn risk, not the scorched-earth feeding you get from synthetic fertilizer. The castings calculator tells you how much castings your beds need; this builder tells you what to blend.
Ratios are by volume. A "part" is any container you like — a scoop, a bucket, a wheelbarrow. Just use the same one for everything.
Want to know exactly what's in your castings? Know Your Castings traces every batch by lot code. Curious about the fungi doing the underground networking? What is Mycorrhizae? And if you want to meet the whole underground workforce, visit the Soil Food Web Explorer. Need the castings themselves? The shop has 1-gallon and 5-gallon sizes.
Honest note: these are tried-and-true home recipes, not lab prescriptions — adjust for your plants and your conditions. Castings are gentle biology, not fertilizer: low burn risk, not no-risk. More is not always better.