Why "Feminised" Plants Still Make Pollen (The Science of Hermaphrodites)

Watch the episode · 4:14

You bought feminised seeds: no males, guaranteed. Then, in week five of flowering, you find pollen. A female plant growing male parts is called a hermaphrodite, and one can seed a whole room. But a 2020 study found something stranger: every seed it made was female.

Source · Punja & Holmes, Front. Plant Sci. (2020)

What a herm is ▶ 0:29

Cannabis is dioecious: males and females grow as separate plants. Females are XX and males are XY, as episode 1 explained, and normally each plant makes just one kind of flower.

A hermaphrodite is a female that also grows anthers, the pollen-making part of a male flower. Usually it is a few, tucked in among the pistils; rarely, whole clusters. Growers call them bananas.

Source · Punja & Holmes, Front. Plant Sci. (2020)

How common? ▶ 1:07

In that 2020 study, researchers watched three commercial strains. From around week four of flowering, anthers appeared on 5 to 10% of the plants.

And they were not duds. Under the microscope the anthers looked just like a male's, and the pollen germinated. The seeds they made sprouted at 90 to 95%. A herm is not a glitch: it is a working male, hiding inside a female.

Why it happens ▶ 1:36

Inside the plant it is a hormone tug of war. Ethylene pushes flowers towards female; gibberellins push them towards male. Whichever side pulls harder wins.

Source · Timoteo Junior & Oswald, Front. Plant Sci. (2024)

Research lists the stresses that can shift a plant's sex: temperature, photoperiod and light, nutrient deficiency, and physical damage. For indoor growers, the usual suspect is light leaking into the dark period.

Source · Flajšman et al., Front. Plant Sci. (2021)

Genetics matter too, and scientists are still hunting the genes. A 2025 preprint, not yet peer reviewed, mapped a region on the X chromosome called Monoecy1.

Source · Toscani et al., bioRxiv preprint (2025)

The twist: feminised seeds ▶ 2:25

Here is the twist: the feminised seeds in your pack were made by a hermaphrodite, on purpose. Breeders spray a chosen female with silver thiosulfate, which blocks ethylene. The tug of war tips, she grows male flowers, and her pollen carries only X chromosomes.

X from the mother, X from the pollen: every seed gets two X chromosomes, female almost every time.

Which explains that 2020 surprise. Seeds from accidental herms grew up female too. A herm is a feminised-seed factory nobody asked for.

There is a catch. Self-pollinating can carry a plant's weaknesses into its seeds, so careful breeders test the offspring, and check them for male flowers, before a line is released.

Source · Timoteo Junior & Oswald, Front. Plant Sci. (2024)

For growers ▶ 3:16

Check every plant weekly from around week four of flowering. Look deep in the buds, in among the pistils, for anthers. Keep the dark period truly dark, and keep stress low and steady. Prevention beats tweezers.

A herm is a female growing anthers; in one study 5 to 10% of plants did it. Hormones and stress tip the balance, and every feminised seed starts with a herm, made on purpose.