# Herm threshold

> The herm threshold is GenetixBay's two-tier herm standard: a 10-plant screening grow with zero herms to be featured, then about 150 or more community-grown plants before a line can be Verified under 2% herm rate.

- Canonical: https://genetixbay.com/knowledge/glossary/herm-threshold.html
- Also written: 2% herm threshold, Verified under 2% herm rate, herm screening, herm rate threshold, hermaphrodite threshold, 2 percent herm rule, herm rate
- Glossary category: GenetixBay terms · Evidence: Supported
- 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"

The herm threshold is GenetixBay's standard for sex stability. It has two tiers, because a small test grow can catch a bad line but can't prove a good one.

## In practice

- **Tier 1, screening.** The breeder (or the Bay's testers) flowers a test grow of at least 10 plants. Any [herm](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), meaning any plant that shows [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) or bare [anthers](https://genetixbay.com/knowledge/glossary/anther.md) ([nanners](https://genetixbay.com/knowledge/glossary/nanners.md)), fails the line for [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md), [the Seed Club](https://genetixbay.com/knowledge/glossary/seed-club.md) and featuring. A line can be reworked and screened again.
- **Tier 2, verified.** Community grow reports on the line are pooled against its batch [GB-IDs](https://genetixbay.com/knowledge/glossary/gb-id.md). Only when they add up to about 150 plants or more, with few enough herms, can the line earn the label **"Verified under 2% herm rate"**. If the pooled rate rises above 2%, the line loses featuring until it's reworked.

Testers record each herm against the batch GB-ID with [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md) and the week of flower, so the rate is data, not hearsay.

## Why two tiers

Ten plants can't tell 2% from 10%. A line that herms 2% of the time shows zero herms in 10 plants about 82% of the time; a line that herms 10% of the time still shows zero about 35% of the time. So a clean 10-plant grow is a screen: it fails obvious problems, and it can't certify a low rate.

To certify, GenetixBay uses a one-sided 95% upper bound on the true herm rate (exact binomial, Clopper-Pearson). "Verified under 2%" means that bound is below 2%:

| Herms seen | Plants needed |
|---|---|
| 0 | 149 |
| 1 | 236 |
| 2 | 313 |

With zero herms the rule of thumb is the "rule of three": the 95% upper bound is about 3/n, so 3/150 = 2%. With one or more herms you need more plants.

## Units and formula

Herm rate (%) = intersex plants / plants flowered x 100. Verified when the one-sided 95% upper bound is under 2%; with zero herms in n plants that bound is 1 - 0.05^(1/n), which drops below 2% at n = 149.

## Myth check

"Some herms are just normal." GenetixBay position: intersex plants are mainly a breeding fault, revealed by stress, not normal behaviour. 5-10% herms in a commercial room means poor genetics. GenetixBay holds best breeding standards, "snobby, and proud of it". See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md), [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md).

## Related terms

[Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md), [Nanners](https://genetixbay.com/knowledge/glossary/nanners.md), [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md), [Seed Club](https://genetixbay.com/knowledge/glossary/seed-club.md), [Test grow](https://genetixbay.com/knowledge/glossary/test-grow.md)

## Read more

- [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md)
- [Seed germination testing and quality control for breeders](https://genetixbay.com/knowledge/breeding/seed-germination-testing-qc.md)

## Sources

1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718