Domakihub Make Aerated Compost Tea: Free Liquid Fertiliser
Turn a bucket of finished compost into a potent, microbe-rich liquid feed in 24 hours — no chemicals required.
Reviewed by Domakihub garden pros · 2026-06-23 · 5 min read
Aerated compost tea (ACT) is one of the most cost-effective soil improvers available to anyone with a compost heap, a cheap aquarium pump, and a little patience. The video above walks through the entire process from start to finish; this article adds the precise steps, timings, and application tips you need to get consistent results. Whether you manage a private garden in Athens, a holiday villa in Crete, or the grounds of a small boutique hotel, ACT gives your plants a measurable boost without spending a euro on synthetic fertilisers.
What Makes Aerated Compost Tea Different
Most gardeners already know that compost improves soil, but simply watering with compost soaking in a bucket (known as passive or anaerobic compost tea) produces a flat, sometimes foul-smelling liquid that can harbour harmful bacteria. Aerated compost tea is different: a continuous stream of bubbles keeps the brew aerobic, which selectively multiplies beneficial fungi, bacteria, and protozoa rather than anaerobic pathogens.
The result is a liquid teeming with microorganisms that colonise your soil, break down organic matter more efficiently, suppress certain soil-borne diseases, and make locked-up nutrients available to plant roots. Scientific trials from Oregon State University and others have shown measurable improvements in plant growth and disease suppression when ACT is applied correctly — especially on sandy or depleted Mediterranean soils.
What You Need Before You Start
The equipment list is deliberately minimal: a 20-litre food-grade bucket, a small aquarium or pond air pump (at least 3–4 litres per minute output), a length of air hose, and a weighted air stone or simple diffuser. For the brew itself you need roughly 500 g of mature, dark finished compost (not fresh material) and a tablespoon of unsulfured molasses — the molasses feeds the bacteria and accelerates population growth. Dechlorinated water is essential: either let tap water sit uncovered for an hour, or use rainwater. Chlorinated water kills the very microbes you are trying to cultivate.
Sourcing mature compost is the one step that matters most. In Greece, well-aged olive or grape pomace compost is excellent if available; otherwise any dark, crumbly, earthy-smelling finished compost will work. Avoid immature or partially composted material, which can introduce weed seeds and undesirable organisms into the brew.
How to Brew Aerated Compost Tea: 5 Steps
- 1
Fill the bucket and set up aeration
Fill your 20-litre bucket with dechlorinated or rain water, leaving a few centimetres of headroom. Place the air stone or diffuser at the bottom of the bucket, connect it to the air hose, and run the hose up and over the rim to your air pump. Switch the pump on and confirm you have a vigorous rolling boil of bubbles across the base of the bucket — weak aeration produces an inferior and potentially unsafe brew.
- 2
Add compost and molasses
Add approximately 500 g of finished compost directly to the water — you can place it loosely in a mesh bag (an old onion net works well) to make straining easier later, or simply tip it in loose. Then add one level tablespoon of unsulfured molasses and stir briefly. The molasses dissolves quickly and gives the microbial population a sugar source to fuel rapid reproduction over the next 24 hours.
- 3
Brew for 24–36 hours, monitoring the foam
Leave the pump running continuously. Within a few hours you should see a light tan foam developing on the surface — this is a good sign of active aerobic microbial activity. If the brew smells like rich earth, everything is working. If it develops a sulphurous or sewage odour, your pump is underpowered or the compost was not mature; discard it and start again. Most brews reach peak microbial density between 24 and 36 hours; beyond 48 hours the food source is exhausted and populations begin to crash.
- 4
Strain and apply immediately
Once brewed, strain the liquid through a piece of hessian, shade cloth, or a paint strainer bag into a clean container or directly into a watering can. Apply the tea to your garden within 30 minutes of stopping aeration — once the bubbles stop, oxygen levels drop and the microbial balance shifts rapidly. Apply as a soil drench around the root zone of plants, or use a sprayer (with the nozzle tip removed to avoid blockages) for a foliar feed on leaves early in the morning.
- 5
Clean your equipment thoroughly
Rinse the bucket, air stone, and hose with clean water immediately after use. Residual organic matter left in the equipment becomes a breeding ground for the wrong organisms and will compromise your next batch. Allow everything to air-dry fully before storing. If you brew regularly — say once every two weeks during the growing season — a quick soak of the air stone in diluted white vinegar every few batches will keep it free-flowing and maintain good bubble distribution.
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FAQ
- Can I use ACT on potted plants and indoor herbs, or only on garden beds?
- ACT works well on potted plants and container herbs — apply it as a gentle soil drench, using roughly 200–300 ml per medium-sized pot. Avoid foliar spraying indoors where there is no airflow to dry the leaves quickly, as prolonged leaf wetness can encourage mildew. On balcony planters and terrace pots, a fortnightly ACT drench during spring and summer will noticeably improve vigour.
- Is aerated compost tea safe to use on vegetables I am about to harvest?
- For root vegetables and low-growing salad crops, stop foliar applications at least 48 hours before harvest and switch to soil drenches only from that point. While a well-made aerobic brew is very different from raw manure tea, good hygiene practice is sensible: wash all produce thoroughly before eating. For fruit trees, climbing vegetables, and anything where the edible part is not in contact with the soil, ACT can be applied freely throughout the season.
- I do not have a garden composter yet — can I use shop-bought compost?
- Yes, though quality varies widely. Look for mature organic compost from a reputable brand — dark, crumbly, and earthy-smelling with no visible undecomposed material. Avoid compost blended with peat or synthetic slow-release fertiliser pellets, as neither contributes to microbial diversity and the latter can skew the brew chemistry. If you are in Greece, look for certified organic compost from agricultural cooperatives, which tends to carry a richer native microbial community than imported products.