How to Make Compost Tea
Compost tea is a simple water extract made from mature garden compost and used promptly around plants. It is traditional, inexpensive and easy to try, but evidence that it consistently improves plant health or prevents disease is limited. Treat it as a mild supplement, not a replacement for sound soil care.
Start with fully mature, sweet-smelling garden compost. It should be dark, crumbly and free from obvious fresh scraps, rather than material still heating in the compost heap. Immature or foul-smelling compost can make an unpleasant brew and is better returned to the bin to finish rotting. Choose a clean bucket, watering can, sieve and water from a water butt if available. Clean equipment reduces the chance of introducing unwanted residues. Make only as much as you can use that day, because compost tea is not a long-storage product. This simple approach is sometimes called a compost extract; it avoids claims that a homemade brew is a reliable cure for plant problems.
Put a few handfuls of mature compost into the bucket and add water until the mixture is loose and easy to stir. Break up clumps with a clean stick, then leave it in a shaded place for several hours. Stir it regularly to keep the mixture moving and exposed to air. Do not seal the container or leave it in hot sun. A gentle, earthy smell is a good sign; a sour, rotten or sewage-like smell means discard the liquid onto the compost heap and start again with better-finished compost. Do not add sugar, milk, manure, fertiliser or other ingredients. They make the process less predictable and are unnecessary for a straightforward garden compost extract.
Strain the liquid through a sieve, old clean cloth or fine mesh into a watering can. Put the remaining solids back onto the compost heap or spread them thinly as mulch around established plants. Dilute the strained liquid generously with water until it resembles weak tea, then use it promptly. Apply it to damp soil around the base of established vegetables, fruit and ornamentals, rather than spraying it over leaves. Soil application is simpler and avoids presenting compost tea as a disease treatment. Avoid using it on seedlings, very young transplants, plants with damaged roots or edible leaves that are close to harvest. Plain water and well-made compost remain the priorities for these plants.
Choose a calm, mild day to apply the tea. Water the bed first if the soil is dry, since liquid poured onto dusty ground may run away from roots. Use the mixture around plants that are actively growing, such as established beans, courgettes, fruit bushes or flowering borders. Apply modestly across the root zone rather than soaking one small spot. Do not use compost tea instead of routine watering, mulching or feeding where these are needed. If rain is expected immediately, wait until after it has passed so the application is not rapidly diluted or washed beyond the root area. A weekly routine is unnecessary; occasional use alongside mature compost is sufficient for most gardens.
Keep expectations realistic. A compost tea may add a little soluble material from the compost, but results differ with the compost, water, weather, soil and plants involved. Research does not show consistent, reliable benefits from home-made compost tea, especially for claims about controlling diseases. Do not use it as a substitute for crop rotation, spacing plants well, removing diseased material, watering at soil level or maintaining healthy soil. If plants are yellow, wilting or failing, inspect for drainage, root congestion, weather damage and nutrient needs rather than relying on a brew. For recurring concerns, seek advice from the RHS or a local garden centre and take clear notes or photographs.
Make compost tea safely and keep the process tidy. Use only compost made from appropriate garden and kitchen plant waste, and do not use compost containing pet waste, meat, dairy products or unknown materials. Wash buckets, sieves and watering cans after use, especially if they are also used for harvesting. Use the brew on soil, not on leaves or crops you plan to pick soon, and never store it for another day. If your main aim is improving fertility, spread mature compost as a mulch instead; it delivers organic matter directly where soil organisms can use it. Compost tea is best regarded as an optional traditional extra, not an essential gardening task.
Frequently asked questions
How long should compost tea steep?
For a simple garden compost extract, several hours with regular stirring is enough. Use it on the same day. Longer standing can lead to unpleasant, low-oxygen conditions, particularly in warm weather. If the mixture smells sour or rotten, do not apply it to plants; add it to the compost heap and clean the container before trying again.
Can compost tea replace fertiliser?
No. Compost tea is variable and generally mild, so it is not a dependable substitute for fertiliser where a crop genuinely needs nutrients. Build fertility with mature garden compost, crop rotation and suitable feeding when needed. Use compost tea only as an optional supplement, and do not expect it to correct poor soil, drought or drainage problems.
Should I spray compost tea on leaves?
It is better to apply a simple home-made compost tea to the soil around established plants. Evidence for leaf spraying is limited, and it can leave residues on edible crops. Avoid using it on seedlings or leaves close to harvest. Good air circulation, sensible watering and prompt removal of diseased material are more reliable plant-care measures.
General guidance for UK home gardens and allotments. Conditions vary by region, soil and season; the RHS or a local garden centre can give site-specific advice. Page updated 19 Sep 2026.