Compost Tea Recipe Calculator Guide
Use this compost tea recipe calculator to scale compost and molasses for aerated compost tea batches. Enter desired batch size in gallons to get compost volume and molasses tablespoons for a basic actively aerated recipe.
How to use the compost tea recipe calculator
Enter total batch size in gallons — the finished tea volume you want after brewing. The calculator returns compost and unsulfured molasses amounts using common home-brew ratios.
Use finished, mature compost and chlorine-free water for best microbial diversity.
Compost tea ingredient formulas
Compost (gallons) = Batch size ÷ 5 (one part compost to five parts water). Molasses (tablespoons) = Batch size × 1 (one tablespoon per gallon of water as microbial food).
These ratios suit basic aerated compost tea brewed 24–36 hours with an aquarium pump and air stone.
- Compost gal = batch gallons / 5
- Molasses tbsp = batch gallons × 1
- Use unsulfured molasses — sulfur inhibits microbes
- Brew 24–36 hours; use within 4 hours of finishing
Worked example
A 5-gallon batch of aerated compost tea: Compost = 5 ÷ 5 = 1 gallon of mature compost in the brew bag.
Molasses = 5 × 1 = 5 tablespoons. Fill the brewer with 5 gallons of dechlorinated water and aerate continuously.
Brewing basics
Suspend compost in a mesh bag inside the brewer so nutrients diffuse without clogging air stones. Maintain constant aeration — anaerobic tea can harbor pathogens and off odors.
Optional additions include kelp meal, fish hydrolysate, or humic acid per organic program guidelines.
Application tips
Apply as a soil drench or foliar spray in early morning. Filter through fine mesh for sprayers. Use within hours of brewing completion while oxygen levels remain high.
- Do not brew with chlorinated tap water without dechlorinating.
- Clean brewer between batches to prevent biofilm buildup.
- Pair with compost calculator for bulk compost orders.
- Not a substitute for balanced soil fertility — use with soil tests.