# Bloom booster

> A bloom booster is a high-phosphorus, high-potassium additive sold for flowering; cannabis trials show a P plateau, so past moderate levels it adds cost and runoff, not yield.

- Canonical: https://genetixbay.com/knowledge/glossary/bloom-booster.html
- Also written: bloom boosters, PK booster, PK boost, flower booster, bud booster, high-P booster
- Glossary category: Nutrients · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

A bloom booster is a supplement, usually high in phosphorus and potassium and often based on [monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md), sold to be added to a base feed during flowering. Labels such as 0-50-30 or "PK 13-14" are typical. Some products also contain sugars, amino acids or plant extracts.

## In practice

A complete base feed already supplies enough phosphorus for flowering cannabis. Independent trials by Shiponi and Bernstein, Westmoreland and Bugbee, and Hershkowitz, Westmoreland and Bugbee found yield and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) plateau at moderate root-zone P, roughly 25-60 mg/L (ppm). Above that, extra P mostly leaves in the [runoff](https://genetixbay.com/knowledge/glossary/runoff.md), and can tie up [zinc](https://genetixbay.com/knowledge/glossary/zinc.md), iron and [copper](https://genetixbay.com/knowledge/glossary/copper.md). Excess K from the same bottle can suppress calcium and magnesium.

## Don't confuse with

- **Bloom base**: a complete flowering feed, not an add-on.
- **Plant growth regulators**: some historic "boosters" contained them; a separate concern.

## Myth check

"More phosphorus in flower means bigger buds" is not supported: there is a plateau (Evidence: Established; GenetixBay house position agrees with the trials). See [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md).

## Related terms

[Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md), [N-P-K ratio](https://genetixbay.com/knowledge/glossary/npk-ratio.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), [Feed chart](https://genetixbay.com/knowledge/glossary/feed-chart.md)

## Read more

- ["Bloom boosters" for cannabis: what's real and what's marketing](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md)
- [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md)

## Sources

1. Westmoreland FM, Bugbee B. 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652
2. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985
3. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323