Compost Tea for Lawns: How to Make and Apply It
Quick Answer
You can make it, and the method is below. You should also know before you start that Maryland tested compost tea on turf and found little effect on growth — and that the molasses most recipes call for is the step that can let human pathogens multiply. The compost is doing the real work. The tea is the questionable part.
At a glance
- Best method
- Non-aerated steep, no added sugar — if brewing at all
- Difficulty
- Low. A bucket, water, finished compost and a strainer
- Time required
- 24–48 hours to brew, then apply the same day
- Evidence on turf
- Little effect on turf growth in University of Maryland testing
- Main risk
- Sugar-fed aerated brews can multiply E. coli and Salmonella
- Better use of the same compost
- A quarter-inch topdressing on the lawn
- Avoid if
- You want a nitrogen source, a fungicide, or a fertilizer substitute
This guide gives you the method because the question deserves a real answer rather than a refusal. It also gives you the evidence, because spending a weekend brewing something that controlled turf work could not distinguish from doing nothing is worth knowing about first.
What Compost Tea Actually Is
Shot: A bucket of dark compost tea with a mesh bag of compost steeping in it.
Alt text: Compost steeping in a bucket of water to make compost tea.
Compost tea is finished compost steeped in water to pull out microbes and soluble nutrients. Maryland Extension describes the aerated version as steeping compost in aerated water to extract beneficial microbes and nutrients. Two forms exist and they are not interchangeable:
- Non-aerated compost tea— compost and water, left to steep. Simple.
- Aerated compost tea— an air pump plus a microbial food source, usually molasses, on the theory that this multiplies beneficial organisms preferentially. Other common additives include kelp meal, fish emulsion, humic acids and various meals.
What the Research Actually Shows
Little
Effect on turf growth
University of Maryland turfgrass testing facility, applied to lawns.
None
Replicated trials establishing efficacy
For aerated compost tea, following the national task force review.
¼ inch
Topdressing that does have evidence
The same compost, used as a soil amendment instead.
Maryland ran the test that matters most here — compost tea applied to lawns, at their own turfgrass testing facility — and reported little effect on turf growth. Broader reviews of aerated compost tea reach a similar place: claims about efficacy have consistently outrun the published replicated evidence.
Why this is worth stating plainly
The Pathogen Risk Nobody Mentions in the Recipes
Adding sugar to the brew can multiply human pathogens
Where residual pathogens are present in the starting compost, nutrient supplements such as molasses have been shown to support the growth of E. coli and Salmonella during brewing.
This is the mechanism that turns a benign-sounding process into a real one. Molasses is added to feed microorganisms — but it feeds whatever is there, and the assumption that aeration selectively favours beneficial organisms over pathogenic ones is exactly the assumption the research has questioned.
The practical consequences: prefer non-aerated tea over aerated, leave the sugar out, use well-finished compost from a known source, and keep applications to landscape plants rather than anything edible. If you have young children or pets using the lawn, weigh that against an input with little demonstrated turf benefit.
How to Make It
If you want to try it, this is the lower-risk version — non-aerated, unsweetened, and applied fresh.
Start with genuinely finished compost
Dark, crumbly, earthy-smelling, with no recognisable material left. Compost that is still active or of unknown origin is where the pathogen concern begins. Avoid fresh manure entirely.Fill a clean bucket with non-chlorinated water
Rainwater works, or tap water left to stand overnight. Chlorine is intended to kill microorganisms, which defeats the purpose of the exercise.Add compost at roughly one part to five parts water
A mesh bag or old pillowcase makes straining easier later. Precision is not meaningful here, since the resulting nutrient content is variable regardless.Steep for 24 to 48 hours, stirring occasionally
Keep it out of direct sun. Do not add molasses, sugar or any other food source — that is the step the pathogen research is about.Strain and use the same day
Pour through mesh or cloth into a watering can or sprayer. Holding it warm for days is the condition under which unwanted populations build. Return the solids to the compost heap or spread them on a bed.
How to Apply It
Water the lawn lightly first so the tea is not landing on dry soil, then apply with a watering can or a coarse sprayer in the early morning or evening. Avoid the hottest part of the day. Nothing needs to be watered in afterwards.
Treat it as an experiment, because that is what it is
Given the evidence, the honest way to use compost tea is to test it rather than adopt it. Apply to a defined section of lawn, leave a comparable section untreated, and look at the two areas across a season. If you cannot see a difference, you have learned something the marketing will not tell you — and it will match what Maryland found.
The Better Use of the Same Compost
Shot: A thin layer of dark compost being raked evenly across an established lawn.
Alt text: Compost being topdressed and raked level across established turf.
Everything the tea is claimed to do, the compost itself does with better support. Topdressing adds organic matter, improves soil structure and water-holding capacity, stimulates microbial activity, and feeds the soil biology an organic fertility programme depends on.
| Approach | Evidence on turf | What you get |
|---|---|---|
| Quarter-inch compost topdressing | Well documented as a practice | Organic matter, structure, moisture retention, biological activity |
| Compost tea | Little effect on turf growth in Maryland testing | Microbes and soluble nutrients — without the organic matter |
| Returning clippings | Well established | Up to around 30% of the lawn's seasonal nitrogen need, for free |
Brewing compost into a liquid removes the organic matter, which is the component with the strongest evidence behind it. Rates, depths and timing for topdressing are in our organic fertilizer guide, and the wider programme is set out in the organic lawn care guide.
Common Questions
Before You Begin
If the goal is better soil, spread the compost. A quarter-inch topdressing costs the same material, takes an afternoon rather than a weekend, and has actual research behind it.
If the goal is trying compost tea because you want to see for yourself, do it non-aerated and unsweetened, use it fresh, and set aside an untreated strip to compare against. That is the version with the lowest risk and the most honest chance of telling you something. What it will not do is feed the lawn, cure disease, or replace the practices that carry an organic programme.
About the Author
Jack is a lawn care researcher and former landscaping crew lead with 20+ years working transition-zone turf. He writes every guide here from university extension publications and turfgrass research rather than product marketing — after learning the hard way that most of what gets passed around on job sites is backwards.
Have a question or topic suggestion? Get in touch.
Sources and further reading
- University of Maryland Extension — Organic Lawn Care and Supporting Pollinators (the turfgrass testing facility result, and the definition of aerated compost tea)
- Ohio State University Extension — Natural Organic Lawn Care (HYG-4031) (compost topdressing practice, clippings supplying seasonal nitrogen, and the absence of useful organic fungicides)
- University of New Hampshire Extension — Organic Turf: Frequently Asked Questions (organic matter targets, topdressing depth, and compost source cautions)
Compost quality and source vary enormously, and that variation is central to the safety question here. If you are unsure about a compost source, your county extension office can advise. How we research and review guides is set out in our editorial policy.