# Does compost tea work for cannabis?

> Compost tea is not a meaningful fertiliser for cannabis, and its disease-control effects are inconsistent. Reviews found some teas suppressed some diseases in some trials, with no reliable recipe, and there are no controlled cannabis trials. Adding molasses, kelp or fish to brew grew E. coli and Salmonella 10- to 10,000-fold in one study. If you use it, apply it to living soil, not flowers, within hours of brewing.

- Canonical: https://genetixbay.com/knowledge/answers/does-compost-tea-work.html
- Topic: Nutrients · Type: How-to
- Evidence: Contested · Status: Draft: awaiting expert review
- Full article: [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md)
- Also asked as: Does aerated compost tea work? | Is ACT good for weed plants? | What are the benefits of compost tea? | Does compost tea feed the plant? | Should I add molasses to compost tea?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

Not reliably. [Compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) 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](https://genetixbay.com/knowledge/glossary/living-soil.md) 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](https://genetixbay.com/knowledge/glossary/chloramine.md) in [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) doesn't gas off on standing; long-contact carbon or ascorbic acid removes it [3].

The house position on sugar applies: [molasses](https://genetixbay.com/knowledge/glossary/molasses.md) 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

1. Build the soil first: compost, castings and [top-dresses](https://genetixbay.com/knowledge/glossary/top-dressing.md) do the feeding.
2. If you brew, use clean equipment and dechlorinated water.
3. Skip or minimise sugary and protein-rich supplements.
4. Apply as a soil drench soon after brewing.
5. 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](https://genetixbay.com/knowledge/systems/living-soil.md)
- Answers: [mycorrhizae](https://genetixbay.com/knowledge/answers/do-mycorrhizae-help.md) · [super soil](https://genetixbay.com/knowledge/answers/what-is-super-soil.md)
- Articles: [water quality and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md)
- Terms: [compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) · [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md)

## Follow-up questions

**Does compost tea add nutrients?** Compost tea adds very little nutrition. It is a dilute water extract of compost, so it carries small amounts of soluble nitrogen, potassium and other ions, far below what a flowering cannabis plant needs. Its value, if any, is biological. Feed living soil with top-dressed amendments and compost itself, and treat tea as optional.

**Is it safe to spray compost tea on buds?** No, do not spray compost tea on cannabis buds. Teas can carry and grow human pathogens: in one study, nutrient supplements added to brewing compost tea made E. coli and Salmonella multiply by 1 to 4 log units. Wet flowers also invite bud rot. Keep teas to the soil, and never to flowers people will smoke or eat.

**Should I add molasses to compost tea?** Molasses in compost tea feeds the microbes in the brew, not the plant, which makes its own sugars by photosynthesis. It speeds microbial growth, including unwanted bacteria, and drains dissolved oxygen faster. If you brew tea, keep any sugar small, aerate well, use dechlorinated water and apply the tea within a few hours.

## Sources

1. Scheuerell S, Mahaffee W, 2002. Compost tea: principles and prospects for plant disease control. Compost Science & Utilization 10(4):313-338. https://doi.org/10.1080/1065657X.2002.10702095
2. Ingram DT, Millner PD, 2007. Factors affecting compost tea as a potential source of Escherichia coli and Salmonella on fresh produce. Journal of Food Protection 70(4):828-834. https://doi.org/10.4315/0362-028X-70.4.828
3. Water Quality Association, 2014. Chloramine fact sheet. https://wqa.org/wp-content/uploads/2022/09/2014_Chloramine.pdf