What Is Compost Tea Good For?

Compost tea has become an increasingly popular organic gardening tool in recent years. This liquid extract provides a concentrated dose of beneficial microbes and nutrients from compost. When sprayed onto plant leaves or watered into the soil, compost tea can offer an array of benefits for plants and gardens.

What Exactly is Compost Tea?

Compost tea is a solution made by steeping compost in water. This process extracts a “tea” full of microorganisms, trace minerals, and organic compounds from the compost. It provides a nutritious tonic that enlivens soils and plants.

There are two main methods for brewing compost tea:

  • Aerobic compost tea – Made by aerating compost and water together for 24-36 hours. This maintains an oxygenated environment ideal for aerobic bacteria and fungi.
  • Anaerobic compost tea – Brewed without aeration for just 12-18 hours. It contains more anaerobic microbes.

Aerobic teas produce higher microbial diversity and counts, with more benefits for plant health. Anaerobic teas can harm plants if not used correctly.

Why Use Compost Tea?

Compost tea concentrates the living powers of compost into a liquid form. This provides a simple way to harness the following advantages:

1. Delivers a Boost of Beneficial Microbes

Compost teas contain large populations of beneficial bacteria and fungi. Typical compost teas host over 10 million microbes per teaspoon, including species like:

  • Pseudomonas – Helps plants acquire nutrients and fight fungal diseases.
  • Trichoderma – Parasitic fungi that prey on plant pathogens.
  • Mycobacterium – Assists with decomposition of organic matter.
  • Bacillus – Produces antibiotics that protect plants from bacterial/fungal infection.

These microbes colonize plant roots and leaves, protecting against pathogens while supporting stronger growth.

2. Provides Nutrients for Plant Growth

In addition to microbes, compost tea contains water-soluble macro and micronutrients. This includes essentials like:

  • Nitrogen, phosphorus and potassium
  • Calcium, magnesium and sulfur
  • Iron, zinc, boron and copper

These minerals nourish plants in a form that is readily absorbed and utilized. Compost tea also contains humic acids that stimulate nutrient uptake.

3. Adds Organic Matter to Soil

The compost particles and sugars in compost tea feed diverse soil organisms. This helps establish rich, living soil biology.

Regular applications can build soil organic matter over time. This improves moisture retention, drainage and nutrient holding capacity.

4. Can Replace Synthetic Fertilizers

The blend of organic nutrients, microbes and humic acids in compost tea provides a natural alternative to chemical fertilizers. When applied at planting time or monthly, it can fully sustain plant growth and vigor.

5. Suppresses Plant Diseases

Certain microbes in compost tea protect plants from disease infection. They occupy space on leaves that pathogens would otherwise infect. Many also release anti-fungal/anti-bacterial compounds.

Applying compost tea weekly or biweekly coats plants with protective microbes, reducing foliar diseases. It also protects against soil-borne diseases like root rot.

How to Brew Compost Tea

Making compost tea is relatively simple. Follow these basic steps:

Choosing a Compost Source

Start with finished compost, sifted into a fine texture. Avoid compost with any trace of ammonia odor, which indicates immaturity.

Manure-based composts like horse, cow or chicken compost make excellent teas. Vermicompost also works very well.


Brew compost tea with plenty of aeration, using:

  • Aquarium air pump and air stone
  • Handheld aerating tool
  • Compost tea brewer kit

Aim for lots of tiny bubbles continuously circulating the tea.

Water & Nutrients

Non-chlorinated water is essential. Dechlorinate tap water by leaving it out overnight.

Add soluble kelp powder or fish fertilizer to provide extra nitrogen and micronutrients.

Brewing Duration

Brew aerobic compost tea for 24-36 hours. Shorter durations don’t maximize microbial growth. Longer can deplete oxygen.

Compost Ratio

Use around 1 cup of compost per 5 gallons of water. More compost adds nutrients but can overload the tea.


Ideally brew tea between 70-80°F. Warmer temperatures allow faster microbial growth. Cooler slows growth.

Straining & Using

Pour finished tea into another container through a fine mesh strainer to remove compost chunks before applying. Use compost tea within a few hours of finishing for best results.

How to Use Compost Tea in Gardens

Compost tea has many versatile applications for gardens and plants including:

Root Drenching

Drench seedlings and transplants at planting time by watering compost tea into their root zones. This inoculates roots with beneficial microbes and nutrients for enhanced establishment.

Soil Amendment

Apply compost tea when preparing garden beds. The microbes condition soil, while the tea’s nutrients provide starter fertilizer for young plants.

Foliar Sprays

Spray diluted compost tea directly onto plant leaves every 2-4 weeks. This coats leaves with protective microbes and delivers nutrients directly into plants.

Compost Activator

Watering fresh compost piles with compost tea introduces concentrated microbial inoculants. This accelerates the composting process and quality.


Add compost tea to hydroponic systems to introduce populations of healthy bacteria/fungi. This stabilizes root zones and outcompetes pathogens.

Always test compost tea on a few plants first to check for phytotoxic effects before wide scale use.

Compost Tea Benefits for Soil

Beyond directly supporting plants, compost tea also enriches and balances soil biology for long term benefits:

1. Inoculates Soil Microbes

Each application of compost tea re-introduces millions of beneficial bacteria, fungi and other microorganisms into the soil. This expands the soil food web foundation supporting healthy plants.

2. Provides Organic Matter

The compost solids and sugars in compost tea are a food source for soil microbes. Over time, this builds soil organic matter as the microbes convert the organic nutrients into humus.

3. Improves Nutrient Availability

The microbes in compost tea (especially Mycorrhizae) make nutrients like nitrogen, phosphorus and iron more plant-available through their metabolic activity in the soil.

4. Unlocks Bound Nutrients

Microbes release acids and enzymes that liberate fixed nutrients like phosphorus that are chemically tied up in the soil. This makes them usable for plants.

5. Binds Heavy Metals

Certain bacteria can bind with heavy metals like lead and mercury in contaminated soils, reducing their toxicity and mobility.

6. Degrades Pollutants

Specialized bacteria consume and digest soil pollutants like petrochemicals, solvents, pesticides, etc. Regular compost tea applications can accelerate bioremediation.

7. Improves Soil Structure

The glue-like secretions and filaments of microbes bind and stabilize loose soils. Plus, the increased organic matter from compost tea improves soil aggregation.

Compost Tea Benefits for Plants

For plants, the diverse microbes and organic nutrients in compost tea offer numerous direct benefits:

1. Stimulates Root Growth

The bacteria Bacillus and Pseudomonas produce hormones that trigger prolific growth of plant roots. This allows plants to better access soil nutrients and moisture.

2. Protects Against Pathogens

Beneficial microbes form thick colonies on root and leaf surfaces preventing pathogens like fungi and bacteria from establishing infections.

3. Boosts Nutrient Absorption

Microbes like mycorrhizae have symbiotic relationships with plant roots allowing improved absorption of nutrients like nitrogen, phosphorus and zinc.

4. Provides Growth Promoters

Microbes release compounds like auxins, cytokinins and gibberellins that regulate plant cell growth and development. This boosts plant vigor.

5. Improves Resiliency

The protective microbial shield and organic nutrition of compost tea strengthens plant immune systems. Plants are more able to resist stresses like drought, extreme temperatures, salinity, etc.

6. Detoxifies Pollutants

Some bacteria can metabolize organic pollutants, heavy metals and salt build up. This protects plants from contamination and supports growth.

7. Supplies Nutrients

The nitrogen, phosphorus, potassium and micronutrients in compost tea provide substantial plant nutrition in a form that plants can immediately absorb.

8. Chelates Nutrients

Organic acids in compost tea chelate/bind minerals into complexes that remain soluble and available to plant roots rather than precipitating in the soil.

Troubleshooting Compost Tea Problems

When brewed correctly, compost tea is very safe for plants. However, there are a few potential issues to avoid:

Overly Anaerobic Tea

Compost tea made without oxygenation tends to accumulate ammonia and organic acids. This can “burn” plants when applied. Ensure plenty of bubbles when brewing.

Immature Compost Source

Compost that is not fully finished may release excessive ammonia or salts into the tea, making it too harsh. Use very mature compost.

High Salt Content

Some compost can have high salt levels, especially manure-based composts. This gets concentrated in the tea. Use compost tested for salt content if unsure.

Dilution Issues

Applying overly concentrated compost tea can damage plants. Mix 2 parts water to 1 part compost tea when spraying onto leaves.

Pathogen Contamination

If the starting compost contains human pathogens like E. coli, these can grow in the tea. Use well-maintained compost, and don’t apply to edible plants near harvest.

Always test a small batch of compost tea on a few plants and wait a few days before large scale use to check for issues.

Maximizing Compost Tea Benefits

Follow these tips to get the most out of each application:

  • Use fresh tea within 6 hours of brewing for highest microbial viability.
  • Apply in early morning or evening to avoid hot sun drying out leaves and microbes.
  • Target soil application in root zones and foliar sprays on undersides of leaves where microbes thrive.
  • Use compost tea 2-4 times per month through the growing season for sustained effects.
  • Ensure plants have adequate nitrogen – microbes consume N as they grow.
  • Combine with mycorrhizae inoculants for amplified root benefits.
  • Cover soil with mulch after applying compost tea to retain moisture/microbes.
  • Rotate compost sources to increase microbial diversity over time.

The Microbial Magic of Compost Tea

Compost tea is one of the simplest ways to translate the living powers of compost into plant and soil nutrition. This microbial tonic energizes plant growth and naturally suppresses diseases. Applying compost tea regularly encourages:

  • More vigorous, resilient plants
  • Reduced pest and disease pressure
  • Lower need for synthetic fertilizers
  • Improved soil biology and fertility

Unleash the benefits of these microbes for your garden!