Compost tea is a beneficial solution made by brewing compost in water. It provides nutrients and beneficial microorganisms that can improve plant and soil health. However, compost tea does not keep forever and will start to degrade in quality after a certain period of time. Here we will look at how long you can store compost tea and what affects its shelf life.
Quick Answers
Compost tea should be used within:
- 24 hours when kept at room temperature
- 3 days when refrigerated
- 6 months when frozen
The shelf life depends on storage temperature, aeration, and adding additives like molasses or humic acid. Frequent aeration and cooler temperatures help keep compost tea viable for longer.
What is Compost Tea?
Compost tea is made by steeping mature, finished compost in water for a period of time, usually from 12-48 hours. This allows beneficial microbes and nutrients to be extracted from the compost into the water. The finished compost tea is a dark brown liquid that smells earthy.
Compost tea contains a diversity of microscopic life including bacteria, fungi, protozoa, and nematodes. These microorganisms help suppress disease, break down nutrients for better plant uptake, and improve soil ecology. The microbes in compost tea are concentrated when brewed properly and can be applied directly to plants or soil as a fertilizer and disease prevention method.
Why Use Compost Tea?
There are several benefits to using compost tea:
- Supplies a diversity of beneficial microbes to soils and plants
- Provides soluble nutrients from the compost
- Can reduce disease pressure and help plants resist infection
- Improves soil ecology and food web
- Non-chemical and organic method of fertilizing
Compost tea is especially helpful for improving poor quality or diseased soils. The microbes and nutrients help remineralize soils and balance soil ecology. Compost tea is suitable for use on lawns, gardens, farms, and orchards when applied correctly.
How is Compost Tea Made?
There are two main methods of brewing compost tea:
Passively Aerated Tea
Passively aerated tea is made by steeping compost in water for 12-48 hours. The compost and water are kept in a container such as a 5 gallon bucket. The mixture is stirred occasionally but is not actively aerated. This method produces compost tea with less dissolved oxygen.
Actively Aerated Tea
Actively aerated tea uses an aquarium pump and air stone to continuously inject oxygen into the brewing tea. The oxygen supercharges microbial growth and activity during the 12-24 hour brew time. This makes tea with higher populations of beneficial microbes.
Active aeration is recommended for best results. Passive tea can still be useful but has fewer microbe species and numbers. Other tips for brewing quality compost tea include:
- Use finished, mature compost
- Use a compost:water ratio of 1:5 to 1:10
- Brew for 12-48 hours
- Keep brewing vessel in cool, shaded area
- Use chlorine-free water if possible
What Affects Compost Tea Shelf Life?
There are several factors that determine how long compost tea will remain viable and effective after it has been brewed:
Oxygen Levels
Compost tea contains aerobic microorganisms that require oxygen. As soon as tea is brewed, the microbes begin consuming oxygen. Without fresh oxygen being added, they will deplete the existing oxygen supply after 1-2 days. This causes unfavorable anaerobic microbes to take over.
Temperature
Warmer temperatures accelerate microbial activity and reproduction. This means oxygen is consumed faster at higher temperatures. Storing compost tea in cool conditions helps slow microbe metabolism and extend shelf life.
Nutrient Content
The microbes in compost tea need nutrients to survive. Brewing with additives like molasses, kelp, or humic acids provides food for the microbes. However, the nutrients get used up over time. Teas made with more “microbe food” tend to have longer shelf lives.
Exposure to Light
Exposure to sunlight can damage some species of microbes, since the clear tea provides no protection from UV rays. Storing compost tea in opaque, light-blocking containers prevents sunlight exposure.
How Long Does Brewed Compost Tea Last?
The expected shelf life of compost tea depends heavily on storage conditions after brewing. Here are the general guidelines for maximum storage times:
Room Temperature Storage
At room temperature without active aeration, compost tea will begin losing quality after 24 hours. It is best to use tea within 12-24 hours when stored at room temperature after brewing.
Refrigerated Storage
Storing brewed compost tea in the refrigerator can extend its shelf life to up to 3 days if kept aerobic by shaking or stirring daily. Keep the container loosely capped to allow oxygen exchange.
Frozen Storage
Freezing compost tea preserves microbe viability for the longest durations. Frozen compost tea can remain effective for 3-6 months when sealed in an airtight container with no headspace. Allow frozen tea to fully thaw before use.
Here is a table summarizing expected compost tea shelf life under different storage conditions:
| Storage Method | Shelf Life |
|---|---|
| Room temperature | 24 hours max |
| Refrigerated, aerated daily | 3 days max |
| Frozen, sealed container | 3-6 months |
How to Tell if Compost Tea Has Spoiled
There are a few signs that indicate compost tea has degraded in quality and is past its prime:
- Color changes – Healthy tea is dark brown. It lightens to tan or gray as microbes die off.
- Cloudiness – Tea may become opaque or milky looking when microbe levels drop.
- Odor – Fresh tea smells earthy. Foul or rotten odors indicate unfavorable anaerobic bacteria are taking over.
- Foam – Excessive surface foam and bubbles can form from high bacterial growth, signaling over-fermentation.
A microscope can also be used to directly observe whether there are still healthy populations and diversity of microorganisms present in aged tea. If the populations have declined, it’s time to make a fresh batch.
Can Spoiled Tea Harm Plants?
Using compost tea past its prime carries little risk of harming plants. The microbial populations simply decrease to low, ineffective levels. There is potential for anaerobic bacteria or fungi to grow, causing minor root issues, but only in very severely spoiled tea.
The main concern with spoiled compost tea is that it no longer provides the intended benefits. Old tea will not impart adequate microbes, nutrients, or disease suppression to treated plants and soils.
Extending Compost Tea Shelf Life
Here are some tips to help brew compost tea with maximum shelf life:
- Active aeration – Continuously inject air into tea during and after brewing.
- Cool storage – Refrigerate or freeze tea immediately after brewing.
- Brew small batches – Don’t make more than can be used within 3 days.
- Opaque container – Store in a container that blocks light.
- Include additives – Add molasses, kelp, or humic acids as microbe food.
- Sanitize equipment – Use chlorine-free water and clean equipment.
Using Stored Compost Tea
It’s ideal to use compost tea immediately after brewing for maximum effect. However, stored tea can still be an effective treatment if used before it spoils completely. Here are some usage tips:
- Shake or stir stored tea vigorously before application to resuspend microbes.
- Apply stored tea at double normal rates to account for reduced microbe levels.
- Avoid foliar spraying old tea – focus on soil drenching.
- Use within 24 hours after thawing frozen tea.
While compost tea eventually loses quality, proper storage methods allow it to remain viable for days to weeks. Follow the guidelines for your storage conditions to get the most life out of your homemade compost tea.
Conclusion
Compost tea provides an organic boost of nutrients and beneficial microbes. However, its shelf life after brewing is limited. The viability of compost tea begins decreasing after 24 hours due to lack of oxygen, nutrient depletion, and microbe die-off. Storing brewed tea in the refrigerator can prolong shelf life to up to 3 days. Freezing is best for long-term storage, allowing compost tea to last for 3-6 months. With appropriate storage methods, compost tea can retain effectiveness for days to weeks after brewing.
