Compost Tea Brewing Ratio Calculator
Created by: Isabelle Clarke
Last updated:
Calculate precise compost tea brewing inputs from your target water volume and brew ratio. Get compost amount, molasses additions, and total brew volume for consistent biological tea batches.
Compost Tea Brewing Ratio Calculator
CompostingCalculate compost, water, and molasses for repeatable tea batches
Related Calculators
What is a Compost Tea Brewing Ratio Calculator?
A compost tea brewing ratio calculator helps you determine how much compost, water, and microbial food source to use for a planned tea batch. It standardizes inputs so your brews stay repeatable across different batch sizes.
Consistent ratios are important because microbial extraction and growth depend on concentration, oxygen availability, and brew duration. This tool makes it easier to avoid underpowered or overloaded brews.
Compost Tea Brewing Formulas
Compost needed: Water Volume ÷ Brewing Ratio
Molasses needed: Water Gallons × Molasses Rate (tbsp/gal)
Total brew slurry: Water Volume + Compost Volume
Common ratio range: 1:10 to 1:20 (compost:water)
Example Calculation
For 20 gallons of water at a 1:10 compost-to-water ratio with 0.75 tbsp/gal molasses:
- Compost needed = 20 ÷ 10 = 2.0 gallons-equivalent
- Molasses needed = 20 × 0.75 = 15 tbsp
- Total brew slurry = 20 + 2 = 22 gallons
- Recommended brew window = 18-30 hours with active aeration
Common Applications
- Garden foliar feeding: Build consistent tea batches before spray dilution.
- Soil drench programs: Scale brew volume to bed and row coverage.
- Microbial inoculation: Standardize small-batch and large-batch systems.
- Greenhouse production: Match brew outputs to application schedules.
Tips for Better Brew Quality
- Use mature, high-quality compost with an earthy smell.
- Maintain strong aeration throughout brewing to support aerobic microbes.
- Apply tea soon after brewing for best biological activity.
- Clean equipment thoroughly between batches to reduce contamination risk.
Frequently Asked Questions
What is the ideal compost tea brewing ratio?
A common starting ratio is 1 part compost to 10 parts water for actively aerated compost tea. Some brewers use 1:15 to 1:20 for lighter extracts. The best ratio depends on compost quality, brew time, and intended use. This calculator helps you size compost, water, and microbial food additions consistently.
How much molasses should I add when brewing compost tea?
Many recipes use about 0.5 to 1 tablespoon of unsulfured molasses per gallon of water. Too little may reduce microbial growth, while too much can create imbalances. Start moderate, aerate well, and avoid overfeeding the brew. This tool calculates molasses based on your selected batch size.
How long should compost tea brew?
Actively aerated compost tea is often brewed for 18 to 36 hours, with 24 hours as a common target. Brew time depends on temperature, aeration strength, and feed rate. Over-brewing can reduce quality as oxygen demand rises. Use smell and foam behavior as quality cues, and apply promptly after brewing.
Can I use chlorinated tap water for compost tea?
You can, but chlorine and chloramine may suppress microbial activity. If possible, dechlorinate water first by aerating or using filtration and conditioners appropriate for chloramine. Starting with cleaner water improves consistency and biological performance, especially in small batches where chemistry shifts more quickly.
How much compost tea does one batch usually make?
Final brew volume is roughly water plus compost solids, though solids settle and occupy less sprayed volume. For example, 20 gallons of water at 1:10 ratio uses 2 gallons-equivalent compost and yields about 22 gallons of slurry. Application-ready volume depends on filtration and dilution method before spraying.
Sources and References
- University extension publications on compost tea preparation and best practices.
- Soil biology and aerobic brewing guidance from sustainable agriculture programs.
- Practical compost tea field manuals and microbial management references.