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Compost Tea Calculator — Recipe, Brew Time & Coverage

Get precise ingredient amounts, brew timing, and application coverage for your compost tea batch

Compost Needed

16 cups

Coverage

5,000 sq ft

Batches

1

Aerated tea uses an aquarium pump for aerobic microbes. Ready in 24 hours.

Compost Tea Recipe

5 gal
batch size
Compost
16 cups
1.0 gal
Molasses
5 oz
unsulfured
Water
4.0 gal
non-chlorinated

Coverage

Per Batch Covers
5,000 sq ft
Batches Needed
1
for 2,000 sq ft

Coverage by Application Rate

Light (0.5 gal/1000 sq ft)10,000 sq ft
Standard (1 gal/1000 sq ft)5,000 sq ft
Heavy (2 gal/1000 sq ft)2,500 sq ft

Brew Timeline (24hr)

Standard: Optimal for aerated tea. Peak aerobic microbial diversity reached around 24 hours.
TimeStageStatus
0–6 hrExtraction beginsNot ready
6–12 hrBacterial growthPartial
12–24 hrPeak diversityOptimal
24–36 hrFungal colonizationExtended
36+ hrOxygen depletion riskOver-brewed

Aerated Brewing Method

FeatureAeratedNon-Aerated
Brew Time24 hours3–7 days
EquipmentAquarium pump + airstoneBucket only
MicrobesAerobic (beneficial)Mixed anaerobic
SmellEarthy, mildStrong, fermenting
Best ForFoliar + soil drenchSoil drench only

Brewing Tips

Water: Use non-chlorinated water. Let tap water sit 24 hours to off-gas chlorine, or use rainwater.
Temperature: Brew at 65–80°F for best microbial activity. Too cold slows growth; too hot kills beneficial microbes.
Use Quickly: Apply within 4–6 hours of finishing the brew. Microbes begin dying once aeration stops.
Application: Apply in early morning or evening to avoid UV damage to microbes. Use a watering can or sprayer.

Example Calculations

15-Gallon Batch, Standard Rate, 2,000 sq ft Garden

Inputs

Batch Size5 gallons
Compost QualityGood
Application Area2,000 sq ft
Application RateStandard (1 gal/1,000 sq ft)
Brew Time24 hours
AerationYes

Result

Compost Needed16 cups (1 gallon)
Molasses5 oz
Water4 gallons
Coverage5,000 sq ft
Batches Needed1

A 5-gallon batch uses 1 gallon (16 cups) of compost and 5 oz of molasses. At the standard rate, it covers 5,000 sq ft — more than enough for a 2,000 sq ft garden in a single batch.

210-Gallon Batch, Heavy Rate, 5,000 sq ft Lawn

Inputs

Batch Size10 gallons
Compost QualityPremium
Application Area5,000 sq ft
Application RateHeavy (2 gal/1,000 sq ft)
Brew Time24 hours
AerationYes

Result

Compost Needed32 cups (2 gallons)
Molasses10 oz
Water8 gallons
Coverage5,000 sq ft
Batches Needed1

A 10-gallon batch with premium vermicompost uses 2 gallons (32 cups) of compost and 10 oz of molasses. At the heavy rate, it covers exactly 5,000 sq ft in one batch.

35-Gallon Batch, Light Foliar Spray, 8,000 sq ft

Inputs

Batch Size5 gallons
Compost QualityGood
Application Area8,000 sq ft
Application RateLight (0.5 gal/1,000 sq ft)
Brew Time24 hours
AerationYes

Result

Compost Needed16 cups (1 gallon)
Molasses5 oz
Water4 gallons
Coverage10,000 sq ft
Batches Needed1

At the light foliar spray rate, a 5-gallon batch covers 10,000 sq ft — enough for an 8,000 sq ft area in a single batch. Use 16 cups of compost and 5 oz of molasses.

Frequently Asked Questions

Q

What is the compost-to-water ratio for compost tea?

The standard ratio is 1:5 by volume — one part compost to five parts water. For a 5-gallon batch, use 1 gallon (16 cups) of compost in 4 gallons of non-chlorinated water. Add 1 ounce of unsulfured molasses per gallon to feed beneficial microbes during brewing.

  • 1:5 ratio by volume: 1 gallon compost per 5 gallons total batch
  • 5-gallon batch: 1 gallon compost (16 cups) + 4 gallons water
  • 10-gallon batch: 2 gallons compost (32 cups) + 8 gallons water
  • Molasses: 1 oz per gallon of total batch (5 oz for a 5-gallon batch)
  • Use non-chlorinated water or let tap water sit 24 hours to off-gas
Batch SizeCompostWaterMolasses
2 gallon6.4 cups1.6 gal2 oz
5 gallon16 cups (1 gal)4 gal5 oz
10 gallon32 cups (2 gal)8 gal10 oz
25 gallon80 cups (5 gal)20 gal25 oz
Q

How long should I brew compost tea?

Aerated compost tea reaches peak microbial diversity at 24 hours. Brew for at least 12 hours to get meaningful colonization, and no more than 36 hours to avoid oxygen depletion. Non-aerated tea takes 3–7 days. After 48 hours without aeration, anaerobic bacteria can produce harmful compounds.

  • 0–6 hours: extraction begins, nutrients dissolve into water
  • 6–12 hours: bacterial populations start multiplying rapidly
  • 12–24 hours: peak aerobic microbial diversity (optimal for aerated tea)
  • 24–36 hours: beneficial fungi begin colonizing (extended brew)
  • 36+ hours: risk of oxygen depletion and anaerobic conditions — stop here
MethodBrew TimeEquipmentBest For
Aerated24 hoursPump + airstoneFoliar spray + soil drench
Non-aerated3–7 daysBucket onlySoil drench only
Q

How much area does a batch of compost tea cover?

At the standard application rate of 1 gallon per 1,000 square feet, a 5-gallon batch covers 5,000 square feet. A light foliar spray at 0.5 gallon per 1,000 sq ft doubles the coverage. Heavy soil drenching at 2 gallons per 1,000 sq ft halves it to 2,500 square feet.

  • Light (foliar spray): 0.5 gal per 1,000 sq ft — 5 gal covers 10,000 sq ft
  • Standard (soil drench): 1.0 gal per 1,000 sq ft — 5 gal covers 5,000 sq ft
  • Heavy (restoration): 2.0 gal per 1,000 sq ft — 5 gal covers 2,500 sq ft
  • Apply in early morning or evening to protect microbes from UV damage
  • Use within 4–6 hours of finishing the brew for maximum microbial benefit
Application Rate5 Gal Covers10 Gal CoversUse Case
Light (0.5 gal/1000 ft²)10,000 ft²20,000 ft²Foliar maintenance
Standard (1.0 gal/1000 ft²)5,000 ft²10,000 ft²Regular soil health
Heavy (2.0 gal/1000 ft²)2,500 ft²5,000 ft²Soil restoration
Q

What is the difference between aerated and non-aerated compost tea?

Aerated compost tea (AACT) uses an air pump to maintain oxygen levels, promoting beneficial aerobic bacteria and fungi. It is ready in 24 hours and can be applied as both foliar spray and soil drench. Non-aerated tea ferments anaerobically in 3–7 days and has a different microbial profile suited mainly for soil drenching.

  • Aerated: uses aquarium pump + airstone, brews in 24 hours, smells earthy
  • Non-aerated: no equipment needed, brews in 3–7 days, stronger smell
  • Aerated tea has higher bacterial and fungal diversity
  • Non-aerated tea contains more fermentation byproducts (organic acids)
  • Never use over-brewed anaerobic tea on edible crops — it may harbor pathogens
Q

Does compost quality matter for compost tea?

Compost quality is the most important factor in tea quality. Premium vermicompost or well-managed thermophilic compost produces tea with 30–50% higher microbial counts than basic yard waste compost. The compost should be dark, crumbly, and earthy-smelling. Avoid compost that is still hot, smells sour, or has visible undecomposed material.

  • Premium (vermicompost): highest microbial diversity, 30–50% more organisms
  • Good (aged thermophilic): well-decomposed, dark, crumbly, earthy smell
  • Basic (yard waste): partially decomposed, lower microbial counts, still effective
  • Never use: hot/active compost, sour-smelling compost, or compost with visible food scraps
  • Vermicompost has 10–20× more beneficial bacteria than standard compost
QualityMicrobial CountBest SourceEffectiveness
BasicModerateMunicipal yard waste70% of optimal
GoodHighHome-aged 6+ months100% baseline
PremiumVery highVermicompost / hot-managed130% of baseline
Q

How often should I apply compost tea to my garden?

Apply compost tea every 2–4 weeks during the growing season for general maintenance. New gardens or stressed plants benefit from weekly applications for the first month. Foliar sprays are most effective in spring and fall when leaf stomata are more active. Soil drenches work year-round to build microbial populations.

  • General maintenance: every 2–4 weeks during growing season
  • New plantings: weekly for first 4 weeks, then biweekly
  • Stressed plants: weekly until recovery, then return to regular schedule
  • Foliar spray: best in spring/fall mornings when stomata are open
  • Soil drench: any time during growing season, including late fall for overwintering

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Last Updated: Mar 9, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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