Hermaphrodites and Sex Reversal in Cannabis – Causes, Detection, Prevention
Because almost all cultivation today uses feminized seed, the tent normally holds female plants. The hermaphrodite a grower meets is therefore nearly always the same case: a female plant that, under stress, additionally forms male anthers inside its flowers. This case decides between a clean harvest and a seeded mess – and it can be spotted early and largely prevented.
Intersex: the female flower with anthers
The practically relevant hermaphrodite is a predominantly female plant that forms individual anthers within its flower clusters – the notorious “nanners”. Behind it is a survival selfing: under perceived threat, the plant secures its own reproduction. The exact trigger mechanism is still not fully understood.
For growing, the consequence is what counts: if such a plant pollinates itself or its neighbours, energy goes into seeds instead of flower and resin – yield and quality drop. The genetics stay female: seeds from a selfing female flower yield almost only female offspring, around 95 % in practice.
Distinction from true sex reversal
To be kept apart from this is full sex reversal – a complete switch of the visible flower type, in principle possible in both directions. It rests on the plant’s sexual plasticity and is relevant above all to breeding and seed production, not to normal cultivation with feminized females. How cannabis sets its sex is covered under Sex Determination; the hormonal mechanism behind it in the article on the hormone Ethylene.
The main triggers
- Photoperiod disruption is regarded as the most critical factor: light leaks, faulty timers or power cuts during the dark period.
- Temperature outside the flowering optimum.
- Mechanical stress: broken branches, transplant shock, hard cut-backs or training at the wrong time.
- Light intensity and spectrum, nutrient extremes, irregular watering.
Whether a plant actually flips under such stress is partly heritable: the genetics set the threshold, the environment supplies the trigger. A variety with a confirmed predisposition to hermaphroditism has, however, not yet been catalogued – and feminized seed from unstable parent lines passes the risk on.
Detection: what and when
Symptoms typically appear around two weeks after the stress event; weeks 3 to 4 of flowering are considered the highest risk, and vigilance pays off until about week 7. Anthers show as small, smooth, ball- to egg-shaped pollen sacs a few millimetres across – clearly distinct from the female pistils, which stick out of the flowers as fine hairs.
Prevention
- Strict, uninterrupted dark period; seal light leaks consistently.
- Stable temperature, no sudden climate or light jumps.
- Avoid hard cut-backs and late defoliation in flower.
- Start from stable genetics and do not reuse labile individuals.