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, meaning any plant that shows male flowers or bare anthers (nanners), fails the line for Bay Lines, the Seed Club 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. 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 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, breeders vs pollen chuckers and Mythbusters.
