Cannabis plants are gendered, or for the botanically-inclined, dioecious. Female plants are particularly prized because they form buds that are rich in cannabinoid content. For most growers, maintaining a crop free of male plants is critical to ensuring that female buds are not pollinated.
Like all plants, however, cannabis has an inherent drive to procreate by propagating seeds. One way that the plant achieves this is by herming, when female plants become hermaphrodite to self-pollinate. The tendency to herm means that growers must take extra care to minimize any stressors that may cause the plant to perceive a threat and change its sex.
What is herming, and why does it happen?
Herming can occur when female plants experience conditions of environmental stress. “Female plants don't actually turn male, they become hermaphrodites,” says Bruce Perlowin, CEO of Hemp, Inc. and seasoned cannabis cultivator. “You have a female plant that develops both reproductive parts so it can pollinate itself.” A hermaphroditic plant, by definition, contains both female and male sex organs.
According to Perlowin, stress is the fundamental cause of hermaphroditic plants, or 'hermies.' “Some examples of stressors would be not enough water, too much water, not enough nutrients, or too much heat. It can happen at any time in the life cycle of a plant from a new plant to a very mature one,” explains Perlowin. The female plant will develop male flowers in response to stress, to ensure seeds are produced before the environmental trigger can kill the plant.
Other stressors that may incite female cannabis plants to become hermaphroditic include disruptions to the photoperiod, dramatic shifts in temperature, disease or pest infestations, the use of toxic pesticides, and physical damage from vigorous pruning.
Herming can also have a genetic component, with some growers viewing plants that are inclined to herm as genetically inferior.
“Herming can also definitely be a genetic problem, but it is not cultivar-specific,” says Perlowin. “You can get the same cultivars from different seed companies, and they will yield different results.” Reputable breeders are more likely to competently sort and select seeds from genetically robust plants with desirable traits.
How can growers prevent hermaphroditic plants?
The vast majority of cannabis growers cultivate the plant to produce sensimilla. Sensimilla refers to female cannabis buds that have not been pollinated by a male cannabis plant. Sensimilla is more potent than seeded cannabis as it contains greater concentrations of essential oils and psychoactive cannabinoids.
When female plants herm, or develop male flowers capable of disseminating pollen, the entire crop is at risk of pollination. Female flowers that have been fertilized by pollen will halt their development to produce seeds, limiting flower production.
Perlowin advises that growers who wish to prevent female cannabis plants from herming must be diligent throughout the plant's grow cycle. For starters, purchase seeds from a reputable company or trustworthy breeder that understands cannabis genetics. While potential environmental stressors must be monitored and minimized, growers should also examine their plants every day for any unusual growth.
“With hemp and cannabis, you have to walk your fields or monitor your plants every single day to ensure that there are no hermaphrodites or pollen on the plants, as it will affect the rest of your grow,” states Perlowin. “It is surprising how fast something can go wrong so it is important to watch closely. If you don't find these plants, you could be jeopardizing not only your crops, but also those of other growers.”
Finally, swiftly remove any male flowers that appear. If the plant has very few male flowers, those flowers can be removed, but the plant will need to be watched closely. Plants with many male flowers should be eliminated entirely.
“We found that it is better to remove the entire plant than cutting off the problematic branches,” explains Perlowin. “We do this by using a large plastic bag to cover the entire plant. Without shaking the plant, we move the bag down to the very bottom of the plant, seal it, cut the plant down at dirt level, then take it off the property.”
How can you tell a male plant from a female plant?
To a non-expert grower, all cannabis seeds look alike. The gender of cannabis plants becomes more readily apparent when the plant approaches the flowering period.
Author Robert Connell Clarke's book Marijuana Botany An Advanced Study: The Propagation and Breeding of Distinctive Cannabis presents clear instructions for differentiating male and female plants. The gender of a cannabis plant is located at the nodes along the main stem.
Male plants can be identified most easily when they begin flowering. The flowers initially appear as a curved claw shape, which soon differentiates into a flower bud containing five radial segments. As the flowers develop, pollen sacs emerge that almost look similar to small bunches of grapes. Eventually, the sepals of the pollen sacs will open to release the pollen.
"When you see a pollen sac, you will know that a female plant is turning male,” says Perlowin. “Oftentimes, you can tell before the pollen sack becomes a problem. You should examine the plant from the very bottom of the plant to the top. It is easy to spot when the pollen sacs are at the top of the plant, but be sure to examine if there are pollen sacs at the bottom.” Male plants additionally grow taller than female plants as they mature and have thicker stems and fewer leaves.
Female plants usually take several days longer than males to develop pistils or female sexual organs. The pistils look like small green seed pods and have white v-shaped stigmas, or thin hairs, which extend from them. Female plants are generally shorter, denser in foliage, and broader than their male counterparts.
Learn more about the parts of the cannabis plant.
Can you turn a male plant female?
The sex of a plant is determined by its genetics before germination even begins. With the sex genetically encoded, there is no way to make a male plant female, or a female plant male. There are techniques that can be used, however, to encourage a male plant to display female characteristics. These techniques require the use of chemicals, such as ethylene, to prompt a hormonal response from the plant.
Elevated levels of female hormones in male cannabis plants can trigger female flowering development. The technique is more effective when applied to male plants that have not yet formed mature flowers. It's also vital to bear in mind that many male marijuana plants are hermaphroditic plants, and distinguishing true males can be very difficult.
Can you clone a female from a male?
A true female cannabis plant cannot be cloned from a male plant. Cloning is a process that is used by breeders to make genetic copies of robust, healthy female plants, reducing the guesswork that sometimes accompanies cannabis cultivated from seed.
For growers who wish to grow female cannabis plants from seed, the availability of feminized seeds can significantly streamline the growing process. Feminized seeds occur as a result of inducing a female plant to herm, then fertilizing another female plant with the pollen. The pollen from the 'hermie' contains only female chromosomes, so that no true males can result from the seed.