# How do I stop my plants from turning hermaphrodite?

> Prevent hermaphrodites by starting with well-bred genetics first, then removing the stresses that reveal weak plants. Choose lines with a published herm rate and plant count, keep the 12-hour dark period fully light-tight, hold canopy temperature under about 30 °C (86 °F), and avoid heavy pruning or drought in flower. A herm is mainly a breeding fault: cull any plant that herms and never breed from it.

- Canonical: https://genetixbay.com/knowledge/answers/how-to-prevent-hermaphrodites.html
- Topic: Diagnosis · Type: How-to
- Evidence: Supported · Status: Draft: awaiting expert review
- Full article: [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md)
- Also asked as: How do I prevent herms? | How to avoid nanners in flower | Stop my plants hermying | What causes cannabis to herm?
- 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

Start with sound genetics, then take away the stresses that reveal weak plants. Buy lines that publish a [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md) with a [plant count](https://genetixbay.com/knowledge/glossary/plant-count-limit.md), keep the 12-hour dark period fully light-tight, and keep the canopy under about 30 °C (86 °F). *House position*: [herms](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) are mainly breeder error, so cull any plant that herms and never breed from it. The stress triggers are *Supported*.

## Why

Genetics comes first. In [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), sex expression has a genetic basis and responds to selection [2], and genome-wide work has mapped [loci](https://genetixbay.com/knowledge/glossary/locus.md) tied to it [3]. A line built on repeated [selfing](https://genetixbay.com/knowledge/glossary/selfing.md), careless feminising or untested crosses carries the tendency into every pack.

Stress is the trigger. Research links interrupted darkness, altered [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md), low temperatures and certain chemicals to [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) on female plants [1]. Heat at the [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) stresses the plant as well [4]. A stable plant next to the same leak stays female, which is why GenetixBay reads stress as a test the plant either passes or fails.

Herms spread their own weakness. Pollen from a herm gives almost all female seed carrying the same tendency [1].

## The numbers

| Control | Target |
|---|---|
| Dark period in flower | 12 h (or 11 h on [13/11](https://genetixbay.com/knowledge/glossary/13-11.md)), uninterrupted, light-tight |
| Leak test | Nothing visible after 5–10 minutes with eyes adjusted |
| [Canopy temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) | Under about 30 °C (86 °F) |
| Herm onset to watch for | Week 4 of flower onwards [1] |
| Line standard | Published herm rate; under 2% needs about 150 plants to verify |

## What to do

1. Buy from breeders who publish tester herm rates with plant counts. Avoid lines of untested crosses of famous cuts.
2. Seal the leaks: zipper ends, duct ports, equipment [LEDs](https://genetixbay.com/knowledge/glossary/led.md). Use a timer you trust.
3. Don't open the tent in the dark period.
4. Keep leaf temperature down at the tops, and keep watering and feeding steady through flower.
5. Do heavy pruning in veg, not mid-flower.
6. Inspect bud interiors and nodes weekly from week 3–4 with a hand lens.
7. If a plant herms, bag it, remove it, record it and tell the breeder.

## Common mistakes

- Buying "free" or untested seed and blaming the tent.
- Keeping a herm clone because it smokes well.
- Running far past the [harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md).
- Calling late [bananas](https://genetixbay.com/knowledge/glossary/nanners.md) normal.

## Related

- Full article: [Hermaphrodite cannabis (bananas and nanners)](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md)
- Answers: [seeds in my buds](https://genetixbay.com/knowledge/answers/why-are-there-seeds-in-my-buds.md) · [can you smoke a hermie?](https://genetixbay.com/knowledge/answers/can-you-smoke-a-hermie.md) · [opening the tent at night](https://genetixbay.com/knowledge/answers/opening-tent-during-dark-period.md)
- Articles: [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) · [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md)
- Terms: [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md) · [herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md)

## Follow-up questions

**Can I stop a herm-prone strain from herming?** You can reduce, but not reliably stop, herming in a herm-prone cannabis line. A perfect environment removes the triggers, such as light leaks, heat and drought, but the tendency is in the genetics and can still show late in flower. GenetixBay's position is that herm-prone lines are mainly breeder error: grow them out once if you must, cull any herm, and replace the line.

**Do feminised seeds herm more than regular seeds?** Feminised seeds herm more only when they come from careless feminising, such as reversing an unproven female or using pollen from a stress herm. Well-made feminised seed from a female proven stable over several runs can be very stable. Ask for the herm rate and plant count from tester grows; GenetixBay disqualifies lines above 2% in tester grows.

**Does stress cause hermaphrodites?** Stress triggers hermaphrodite flowers in cannabis plants that are already susceptible; it does not make a well-bred female herm. Research links interrupted darkness, altered photoperiods, low temperatures and chemicals to male flowers on females, yet the same light leak leaves a stable clone beside it untouched. Fix the stress to protect the room, and cull the plant that failed the test.

## 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
2. Faux AM, Berhin A, Dauguet N, Bertin P. 2014. Sex chromosomes and quantitative sex expression in monoecious hemp (Cannabis sativa L.). Euphytica 196(2):183-197. https://doi.org/10.1007/s10681-013-1023-y
3. Petit J, Salentijn EMJ, Paulo MJ, Denneboom C, Trindade LM. 2020. Genetic architecture of flowering time and sex determination in hemp (Cannabis sativa L.): a genome-wide association study. Frontiers in Plant Science 11:569958. https://doi.org/10.3389/fpls.2020.569958
4. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x