Short answer
Not reliably. Compost tea carries too little nutrition to feed cannabis, and its disease-suppression effects vary from trial to trial with no dependable recipe [1]. No controlled cannabis trials exist. It is harmless on living soil if brewed cleanly and used fresh, but it is not a substitute for amendments. Contested.
Why
Compost tea is a water extract of compost, brewed with or without aeration. It is dilute: whatever nutrients it carries are a small fraction of a flowering plant's demand.
The disease claims are mixed. A major review found that some teas suppressed some plant diseases, but results depended on compost, brewing method, crop and pathogen, and no single recipe worked across systems [1].
Food safety matters. When commercial nutrient supplements were added to brewing tea, E. coli O157:H7, Salmonella and faecal coliforms grew by 1–4 log units (10- to 10,000-fold) [2]. That is a strong reason never to spray tea on flowers.
The microbes are fragile. Chloramine in tap water doesn't gas off on standing; long-contact carbon or ascorbic acid removes it [3].
The house position on sugar applies: molasses feeds microbes, not the plant.
The numbers
| Factor | Grower practice |
|---|---|
| Brew time, aerated | 24–36 h |
| Water | Dechlorinated, chloramine removed |
| Use within | ~4 h of brewing |
| Where | Soil surface or drench only |
| Flowers | Never |
What to do
- Build the soil first: compost, castings and top-dresses do the feeding.
- If you brew, use clean equipment and dechlorinated water.
- Skip or minimise sugary and protein-rich supplements.
- Apply as a soil drench soon after brewing.
- Judge it on your own side-by-side plants, not on promises.
Common mistakes
- Treating tea as the plant's feed.
- Spraying tea on buds in flower.
- Brewing with chloraminated tap water.
- Leaving tea standing for days, then using it.
Related
- Full article: Living soil
- Answers: mycorrhizae · super soil
- Articles: water quality and chloramine
- Terms: compost tea · living soil
