Short answer
- Compost for compost tea should be finished, dark, crumbly compost that smells like fresh soil, not unfinished material, liquid draining from a pile, or raw manure. Start with about one part compost to nine or ten parts clean, drinkable water, strain the liquid, and use it promptly on the same day brewing finishes. Brew aerated tea for about 24 to 48 hours with a pump running continuously, or steep non-aerated tea for about five to eight days with regular stirring. Use the tea mainly as a soil drench, keep it off the edible parts of food crops unless you can meet the food safety conditions in this guide, and never drink compost tea. Tea is an extract of compost, so it cannot be better than the material it starts from, and extension services describe the evidence for disease suppression as mixed and inconsistent. It may give plants a light nutritional boost, but it is not a proven cure for disease, a guaranteed way to raise yields, or a replacement for finished compost applied directly to soil.
What Compost Tea Is, and What It Is Not
Gardeners use the term for several different liquids, and some of them should never go near food crops. Compost tea is not leachate, the dark liquid that drains out of the bottom of a pile. The University of Vermont Extension warns that leachate may contain organisms that can cause illness, so it is not suitable for spraying on food crops. Compost tea is also not manure tea, a water extract of uncomposted animal manure. Louisiana State University Agricultural Center (LSU AgCenter) states that manure teas should never be used for crops grown for human consumption. Only fully finished compost belongs in a tea brew. Compost tea is also not plant tea, a water extract of fresh, uncomposted plant material such as comfrey leaves. Finally, a quick compost extract, mixed and strained at once, is not the same as a brewed tea, which ferments for hours or days, sometimes with added microbial food sources such as molasses, kelp, or fish hydrolysate.
Choosing Compost for Tea
Selection deserves more care than any other step, because a batch brewed from poor compost will not become good tea through longer brewing, stronger aeration, or extra additives. Finished compost for tea should be dark brown to black, loose, and crumbly, like rich garden soil. It should smell earthy and pleasant, contain no recognizable food or whole leaves, and feel damp but not dripping wet. Compost still hot in the center of the pile is still decomposing, so let it cool and cure first. A sour or ammonia smell means it is not ready.
The University of Vermont Extension notes compost for tea should not be more than nine to twelve months old, and that compost from horse, cattle, and poultry manure performed better in some disease suppression studies than compost from other feedstocks. That does not make manure based compost automatically safe. Very old compost left exposed for years is a weak starting point, while fresh, fully finished compost is better. Keep finished compost covered and dry.
Feedstocks shape the microbes in finished compost. Soft green materials tend to favor bacteria, while woody material tends to favor fungi, but garden writers sometimes overstate matching teas to plants by this balance, which no home test here can measure. A diverse pile gives a more diverse starting compost than a pile made from one material alone. Fully finished worm castings are also a good choice.
Do not brew tea from compost that contains, or that you suspect contains, raw or unfinished manure, pet waste, treated or painted wood, diseased plants that were never hot composted, herbicide treated material, meat, dairy, fats, or glossy printed paper. A pile that never heated up cannot be relied on to have removed pathogens or weed seeds. If you do not know how a batch of compost was made, do not use it for tea on food crops. Use it, if at all, as ordinary soil amendment for ornamentals, or return it to an active pile to finish.
Bought bagged compost can work if it is genuinely finished, earthy smelling, and free of debris. Avoid mostly bark or peat products, and potting mix. When in doubt, brew a small test batch for ornamentals first.
Before brewing, screen the compost through quarter inch hardware cloth, keeping only the fine, crumbly fraction. Measure loosely, and start with about one part compost to nine or ten parts water, matching the nine to one ratio in a two year Rodale Institute and Pennsylvania State University study described by the University of Vermont Extension. No extension source prescribes a single ratio, so treat this as a starting point, and dilute the finished tea if it looks very dark.
Water: The Second Ingredient
Many garden guides advise letting tap water stand uncovered for a day, or aerating it briefly, so chlorine can dissipate, since chlorine can harm the microbes you are trying to encourage. That advice is reasonable for chlorine treated water, but less certain for water treated with chloramine, which does not dissipate by standing in the same way. Check with your local water supplier if you want to be sure which disinfectant it uses. Use room temperature water, and never brew in a container that has held chemicals, pesticides, or cleaning products.
Aerated Tea Versus Non-Aerated Tea
LSU AgCenter names the two primary methods plainly: aerated tea uses agitation or forced air to maintain an oxygen rich atmosphere, while non-aerated tea steeps with no effort to maintain an oxygen rich environment. The University of Vermont Extension adds that it is not clear whether aeration is necessary, that it can speed up production but adds cost and complexity, and that very few studies have compared the two methods directly. Neither has been shown consistently better across crops and conditions.
| Feature | Aerated compost tea | Non-aerated compost tea |
|---|---|---|
| How it works | Air pump bubbles air through water while compost steeps in a mesh bag | Compost steeps in still or occasionally stirred water, with no pump |
| Typical brewing time | About 24 to 48 hours | About five to eight days, up to one to three weeks in some extension descriptions |
| Main risk | Additives can feed harmful organisms; a pump failure can turn the brew anaerobic quickly | Long, low oxygen steeping can favor unwanted microbes; a foul smell means discard |
Aerated tea, often shortened to ACT, keeps oxygen high so aerobic organisms stay active. The classic home setup is a clean five gallon bucket, an aquarium air pump sized for that volume, tubing, air stones, and a mesh bag holding the compost, with the pump running continuously. Common additives named by LSU AgCenter are molasses, soluble kelp, yeast, humic acid, and fish hydrolysate. They are meant to feed microbes, but they carry a warning found in every extension source here: additives can increase both good and bad microorganisms. The University of Vermont Extension advises avoiding additives for food crops, especially simple sugars such as molasses. If additives are used, it advises testing sample batches against the United States Environmental Protection Agency recreational water quality guidelines for coliform bacteria, and warns that untested additive tea should not be followed by harvest for 90 to 120 days, as with raw manure on organic farms.
During aerated brewing, the liquid should turn coffee brown, bubble on the surface, and smell earthy and sweet. A sharp, sour, rotten egg, or putrid smell means the brew has gone anaerobic. Do not try to rescue it by aerating longer or diluting it. Discard it on an ornamental bed or back onto the compost pile, away from food crops, clean the equipment, and start again. Check the pump a few times during the brew, since a pump that stops overnight can cause the same failure.
Non-aerated tea, often shortened to NCT, is the older, simpler method. Compost in a mesh bag or cloth is suspended in water and left to steep, stirred once or twice a day by some gardeners and left undisturbed by others. The University of Vermont Extension notes at least five to eight days may be needed, while Virginia Cooperative Extension describes one to three weeks. Cooler water, coarser compost, and less stirring all slow the process, so judge readiness by brown color and earthy smell rather than the calendar. Virginia Cooperative Extension recommends non-aerated tea over aerated tea for home gardeners, and restricting its use to landscape plants rather than edibles, since a home brew cannot be tested easily.
Step by Step: Brewing a Home Batch
These steps describe one batch in a five gallon bucket. Scale compost and water together for a larger container, keep the same ratio and hygiene steps, read the food safety section before brewing for food crops, and decide in advance whether this batch is for ornamentals only. You need a clean five gallon bucket that has never held chemicals, a mesh bag or clean cloth, finished compost that passes the tests above, clean potable water, a strainer, a watering can or sprayer, and, for aerated tea only, an aquarium air pump with tubing and air stones. Brew out of direct sun, where the bucket will not be knocked over and children and pets cannot reach it.
First, clean and sanitize the bucket, bag, tubing, and air stones: wash with hot soapy water, rinse with clean water, and air dry. Sanitizing matters because the University of Vermont Extension lists sanitized equipment among its food safety recommendations, and old residue can seed a new brew with unwanted organisms. Second, fill the bucket with clean potable water, leaving a few inches of headroom. If you let tap water stand to reduce chlorine, do that before adding compost. Third, put about one part loose, screened compost into the bag for every nine or ten parts of water, roughly six to nine cups for a five gallon bucket filled with about four to five gallons of water. Tie the bag closed, lower it into the water, and, for aerated tea, position the air stones so bubbles rise through and around the bag.
Fourth, for aerated tea, start the pump, confirm strong, steady bubbling, and keep it running continuously. Brew without additives if the tea may reach food crops. For ornamentals only, keep any additive amount small, follow the product label where one exists, and accept the added food safety limits above. This guide gives no specific additive dose, because extension sources do not agree on one. For non-aerated tea, cover the bucket loosely and stir once or twice a day with a clean stick. Stirring adds a little oxygen, but it does not make a non-aerated brew aerated.
Fifth, brew for about 24 to 48 hours if aerated, or at least five to eight days if non-aerated, longer when water is cool or compost is coarse. Earthy and coffee brown is the expected result, and a foul smell means the batch has failed and must be discarded. Sixth, remove the bag, let it drain over the bucket, strain into a clean container, and return the spent solids to the compost pile or spread them as mulch on an ornamental bed. After every batch, wash all equipment with hot soapy water, rinse, and dry fully. Do not leave wet tea residue in a sprayer, since it will go anaerobic and contaminate the next batch.
Applying Compost Tea
A soil drench is the simplest and safest application. Pour strained tea slowly onto the soil around the base of plants so it soaks into the root zone rather than running off. Water very dry soil lightly first, apply in the cooler parts of the day, in the morning or evening, and avoid applying before heavy rain. Tea supplements good soil care, and does not replace watering, mulching, or feeding with finished compost. No extension source prescribes a single dilution rate for home tea. A common home practice is to use strained tea undiluted as a soil drench at the one to nine or one to ten ratio, and to dilute it with an equal part of clean water if it looks very dark or thick, or for seedlings or tender transplants. Keep notes on each batch, including compost source, ratio, brewing time, and plant response.
A foliar spray means spraying diluted tea onto leaves with a pump sprayer, covering upper and lower surfaces. Extension guidance counsels restraint. The University of Vermont Extension notes filtration is required before foliar application, since solids clog equipment and sit on leaves. The Piedmont Master Gardeners advise not spraying tea directly on edible plant parts, and Virginia Cooperative Extension recommends restricting home tea to landscape plants. Keep foliar spraying for ornamentals, strain carefully, spray in the cooler parts of the day, and test on a few leaves first. Do not spray in hot midday sun, on rain wet leaves, or onto lettuce, herbs, berries, or any crop eaten raw. For food crops, a soil drench kept off edible parts is the more defensible choice, and only under the food safety conditions below.
Use brewed tea promptly. The University of Vermont Extension warns tea has a short shelf life because available oxygen is used up and the tea turns anaerobic, killing beneficial bacteria. The Piedmont Master Gardeners advise using it immediately after processing, before the microbial community exhausts the oxygen supply. Apply tea the same day brewing finishes, within a few hours of straining. Do not store it for days, keep a leftover batch for next weekend, or rely on refrigeration to preserve it. If you cannot apply a finished batch that day, discard it on an ornamental bed or back onto the compost pile and brew fresh when you can use it.
Storing Compost, Not Tea
Finished compost stores well, and brewed tea does not. Store finished compost dry, covered, and protected from standing water. Avoid storing wet compost in sealed plastic bags for long periods, since trapped moisture and low oxygen can turn it sour. If stored compost develops a foul smell, do not brew tea from it. Brewed tea has no storage life worth planning around: once brewing stops, oxygen falls and the liquid can smell foul by the next day. Brew only as much as you can apply on the day it finishes, and pour any small remainder onto an ornamental bed or back onto an active pile, away from food crops, then clean the container.
Food Safety and Pathogen Caveats
The University of Vermont Extension, following National Organic Standards recommendations, lists these risk reduction steps for food crops: use only potable water to make and dilute tea; sanitize all equipment; make tea only from compost that has maintained at least 131 degrees Fahrenheit (about 55 degrees Celsius) for three days and has been mixed so all of the pile or windrow has heated up; and avoid additives, particularly simple sugars such as molasses. If additives are used, sample batches should be tested to meet the Environmental Protection Agency recreational water quality guidelines for coliform bacteria. If additive tea is untested or fails testing, food crops may not be harvested until 90 to 120 days after application, as with raw manure on organic farms. The 120 day interval applies where the edible portion has direct contact with the soil surface or soil particles, and the 90 day interval where it does not, following the raw manure restrictions quoted by Virginia Cooperative Extension from the Organic Materials Review Institute.
LSU AgCenter adds that most compost teas are not approved by the Environmental Protection Agency for use on edible crops, and that use of teas with additives on commercial fruit and vegetable production is in most instances prohibited. Virginia Cooperative Extension recommends restricting home tea to landscape plants rather than edibles, and non-aerated tea over aerated tea for home gardeners who brew at all.
A cautious home policy follows from this. For ornamental beds, lawns, shrubs, and trees you will not eat, tea made from finished compost and potable water with clean equipment is a reasonable garden experiment. For food crops, the safest choices are to use finished compost directly as a soil amendment instead of tea, to keep any tea application to a soil drench that does not touch edible parts, to brew without additives, to use only compost from a pile known to have held the heating standard above, and to wash all produce thoroughly before eating. Never spray tea on lettuce, herbs, soft fruit, or any crop eaten raw. Never drink or taste compost tea, and never let children handle brewing equipment or finished tea. Wash hands thoroughly after handling compost or tea. If anyone in the household is pregnant, very young, elderly, or immunocompromised, keep tea away from food crops they will eat, and rely on finished compost applied to soil instead.
What the Evidence Does and Does Not Support
LSU AgCenter lists the claims commonly made for compost tea, including increased soil microbe populations and diversity, higher yields, increased nutrient availability, reduced fertilizer, compost, and water use, disease control and suppression, and increased root growth. It then states that the only benefit with scientific research substantiation is disease control and suppression, and even there only a few studies have shown slight suppression under laboratory conditions. Its conclusions are blunt: science and the compost tea industry disagree on effects and benefits; there is no scientific evidence for most claims; there is no scientific evidence for preferring tea over compost itself; and home production and use often carries the risk of human pathogens.
The University of Vermont Extension describes a two year Rodale Institute and Pennsylvania State University study. Aerated tea was brewed at nine parts water to one part compost, with kelp, humic acid, and fish hydrolysate added, and mechanically aerated. In year one, about 50 percent suppression of powdery mildew was observed in treated grape plots, with a slight reduction in gray mold and an increase in downy mildew at one vineyard. The same tea failed to suppress powdery mildew on Howden pumpkins in year one, though it reduced pathogen colonies in year two, and it did not reduce late blight severity on Superior potatoes when disease was present in year two. The authors concluded the tea offered more measurable benefits in stimulating crop growth, yield, and quality than in suppressing disease, and that its efficacy, consistency, and practicality for disease management needed to evolve considerably before recommendations could be made to growers.
Troubleshooting and Common Mistakes
| Problem | Likely cause | What to do |
|---|---|---|
| Tea smells sour, sharp, or like rotten eggs | Oxygen ran out, pump failed, brew ran too long, or compost was unfinished | Discard on an ornamental bed or the compost pile, clean equipment, start again with finished compost |
| Tea smells like ammonia | Starting compost was too rich in fresh green material or manure and not finished | Do not use it for tea; return the compost to an active pile to finish |
| Pump stops during an aerated brew | Power interruption, clogged air stone, or kinked tubing | If brief, restore aeration and judge by smell; if foul or stopped for many hours, discard it |
| Sprayer keeps clogging | Solids in the tea, or a nozzle too fine for the liquid | Strain twice through finer cloth, use a coarser nozzle, or apply as a soil drench |
| Leaves spot after foliar spraying | Spray in hot sun, tea too concentrated, or leaves already stressed | Stop foliar spraying, rinse leaves with clean water, switch to a diluted soil drench on ornamentals |
| No visible change after tea | Tea is a light supplement, not a fertilizer, and effects are often small or absent | Do not increase dose or frequency; check soil, water, light, and direct compost application |
The most common mistake is starting with the wrong material: unfinished compost, leachate, raw manure soaked in water, and compost of unknown origin are all unsuitable, and no brewing trick fixes them. The second is adding sugary additives to a brew for food crops and spraying it on leaves you will eat. The third is storing brewed tea, which is a same day product. The fourth is over application: repeated drenching, spraying in hot sun, or applying before heavy rain wastes tea and increases runoff. The fifth is expecting tea to cure disease. If a plant shows serious disease symptoms, identify the problem properly, remove badly affected material, improve air flow and watering, and seek local extension advice. A related mistake is confusing tea with fertilizer. Tea at a one to nine or one to ten ratio is mostly water, so it does not supply nutrients at fertilizer levels, and it is no reason to skip soil testing or direct compost application.
Frequently Asked Questions
What compost is best for compost tea?
Finished, dark, crumbly, earthy smelling compost from a well managed pile is best, ideally not more than nine to twelve months old and made from a diverse mix of materials. Fully finished worm castings are also a good choice. Avoid unfinished compost, sour or ammonia smelling compost, leachate, raw manure, and compost of unknown origin, especially for tea that may reach food crops.
What is the best compost to water ratio for compost tea?
Start with about one part loose, screened compost to nine or ten parts clean potable water, matching the nine to one ratio in the Rodale Institute and Pennsylvania State University study described by the University of Vermont Extension. No extension source prescribes a single exact ratio, so treat this as a starting point, dilute the finished tea if it looks very dark, and keep notes so you can adjust for your own compost and plants.
How long should compost tea brew?
Aerated tea generally brews for about 24 to 48 hours with continuous aeration. Non-aerated tea needs at least five to eight days according to the University of Vermont Extension, and up to one to three weeks in Virginia Cooperative Extension descriptions, depending on temperature and compost. Judge readiness by brown color and earthy smell, and discard any batch that smells foul.
Should I add molasses to compost tea?
Molasses and other sugary additives can increase microbial numbers, but they can also feed harmful organisms. The University of Vermont Extension advises avoiding additives, especially simple sugars such as molasses, for food crops, and LSU AgCenter notes additives increase both good and bad microorganisms. For food crops, brew with compost and water only. For ornamentals, additives are a personal choice, but untested additive brews should be kept away from anything you will eat.
Can I spray compost tea on vegetable plants?
Use restraint. Extension guidance recommends keeping tea off edible parts, restricting home tea to landscape plants where possible, and using a soil drench rather than a foliar spray for food crops. If you apply tea near food crops, brew without additives, use only compost from a pile known to have held at least 131 degrees Fahrenheit for three days with full mixing, use only potable water and sanitized equipment, keep tea off edible parts, and observe the 90 to 120 day harvest intervals for untested additive brews. When in doubt, use finished compost directly on the soil instead.
How long does compost tea last after brewing?
It does not store well. Use it promptly on the same day brewing finishes, within a few hours of straining. Once aeration stops, oxygen falls and the tea turns anaerobic, which kills beneficial bacteria and can favor unwanted organisms. Do not save leftover tea, and do not rely on refrigeration to preserve it.
Keep reading: How to Start a Compost Bin
Sources & references
- University of Vermont Extension. "Compost Tea to Suppress Plant Disease." Fact sheet on what compost tea is, aerated and non-aerated methods, brewing times, food safety recommendations, and the Rodale Institute and Pennsylvania State University study results. Accessed 1 November 2026. https://www.uvm.edu/vtvegandberry/factsheets/composttea.html
- Louisiana State University Agricultural Center (LSU AgCenter). "Composting Series: Compost Tea." Publication 3838-E, April 2022. Definitions, the two primary methods, common additives, claims made for tea, evidence assessment, and cautions on edible crops and pathogens. Accessed 1 November 2026. https://www.lsuagcenter.com/articles/page1651066738620
- Virginia Cooperative Extension, Master Gardener program of Northern Virginia. "Garden Myth Busters! Compost Tea." By Rachel Vecchio and Kirsten Conrad, 29 August 2019. Aerated and non-aerated brewing times, evidence assessment, raw manure restrictions, and the recommendation to restrict home tea to landscape plants. Accessed 1 November 2026. http://mgnv.org/intern-projects/garden-myth-busters-compost-tea/
- Piedmont Master Gardeners (Virginia Cooperative Extension affiliated). "The Truth About Compost Tea: Making it, Using it, and What to Expect from it." Guidance on aerated brewing, immediate use, equipment cleaning, and keeping tea off edible plant parts. Accessed 1 November 2026. https://www.piedmontmastergardeners.org/article/the-truth-about-compost-tea-making-it-using-it-and-what-to-expect-from-it/
