Sexing Cannabis: Differences Between Male vs Female Plants

You’ve been growing vegetables in your backyard for years. So when you’re sick of paying big money for your weed, you figure it shouldn’t be a big deal to grow cannabis plants, too.

Sure, gardeners always have to pay attention to their crops’ peculiarities. Celery is more sensitive to temperature than any other vegetable; cucumbers are an insect infestation waiting to happen; unhappy cauliflower plants split into lots of small heads or turn brown.

But when you’re preparing to grow marijuana, you’ll have to deal with a question you’ve probably never dealt with before.

Is it a female or male plant?

Cannabis is one of the relatively-rare plant species that is dioecious, meaning the plants have distinguishable sexes. And determining your plants’ sexes as soon as possible is crucial to your grow.

It’s time for the “birds and bees” talk.

Cannabis Plants and Sex

About 90% of all flowering plants have both male and female sex organs. Those organs usually mature at different times, so the plants don’t end up inbreeding.

When a species is dioecious, male and female flowers are produced on different plants. Asparagus, papaya, and date palms are among the few familiar species that fall into that category — along with cannabis.

Weed plants can even turn out to be hermaphrodites, meaning they have both male and female organs and are able to pollinate themselves. That usually happens when the plants have experienced environmental stresses like light disruption, drastic temperature changes, or physical injury.

In the natural world, of course, both males and females are necessary for the continuation of a species. That’s certainly true in the weed world.

Male cannabis plants are crucial to any breeder’s cultivation program, not just because they’re male. They contain cannabinoids like THC and CBD (interestingly, primarily concentrated in the plants’ leaves). They contain terpenes that provide desirable traits like disease resistance. They provide potency, genetic diversity, and quality when bred.

Here’s the problem, though: growers don’t want male plants in their crops.

The Problems with Male Weed Plants

There are two reasons why including male cannabis plants in a grow is a very bad idea.

First, males don’t produce the trichome-laden flowers we associate with marijuana. Their leaves are great for making hash, concentrates, and edibles, but that’s not what most growers are after. They harvest and sell beautiful buds, and males don’t produce them.

Even more importantly, males obey their biological imperative. When they’re in a grow with female plants, they’ll pollinate the females — and fertilized female plants divert their energy to making seeds, not growing potent buds. There will be fewer flowers to harvest, and it will be significantly less potent.

In short, male plants (and hermaphrodites) can virtually destroy the value of a weed crop.

Commercial producers, and smart home growers, take pains to eliminate that possibility. They use feminized seeds or grow from female clones instead of using regular seeds. But even then, male plants can still sneak into a grow, and it’s crucial to remove them as soon as possible.

The sex of a plant becomes obvious during the flowering stage. Males produce pollen sacs that look like little balls near the base of their leaves. Females produce the sinsemilla (seedless buds) you want to see on your plants.

By that point, though, it may be too late. Males start releasing pollen a few weeks into flowering. Sexing your plants much earlier is the best way to ensure productive grow.

Early Signs of Male and Female Cannabis Plants

To separate males from females early in the growing cycle, you may have to become a detective just like the ones you see in old movies. That means using a magnifying glass or jeweler’s loupe to look for evidence if you’re doing your investigation early in the vegetative stage.

The evidence you’re searching for? The pre-flowers that grow on weed plants in the nodes of the plant. That’s the “V,” where stems branch out from the stalks. Pre-flowers are most often found toward the top of the plant, but some may grow lower.

Cannabis pre-flowers begin to grow between three and four weeks after germination on male plants and between the fourth and sixth week for females. They’re tiny, particularly at first, so you have to look carefully.

Male Plants in the Vegetative Stage

Let’s start with male pre-flowers. They’re immature pollen sacs, and when they first appear, they look much like a spade (the card suit, not the old SNL actor). Some may be rounder and look more like a tiny ball. Often, they appear at the end of a small stem.

Later in the vegetative stage, the sacs will grow in clusters without pistils (white hairs, sometimes called stigmas) emerging from them. That’s a sure sign that the plant should be immediately removed from the grow.

Female Plants in the Vegetative Stage

A couple of weeks after, male plants signal their sex, and female plants follow suit. Their pre-flowers (called bracts) look more like tiny cucumbers or pears (with a wide bottom), but what makes them distinctive and identifiable are the white pistils that grow out of them. They use the pistils to catch pollen when they’re in the flowering stage.

There will usually be one or two pistils, but it can take them a few days to appear after the pre-flower emerges. It’s worth the wait. That lets you be sure that you have a female plant that should remain in your crop.

How to Spot Hermaphrodites

Unfortunately, you can’t tell that a weed plant is a “hermie” until the flowering stage. Until then, they look like female plants.

Once your plants start to flower, pay close attention to the buds. You’re looking for round balls growing on the end of stalks right next to the female flowers; the round ones are male flowers, while the teardrop-shaped ones with pistils are female.

Late in the flowering stage, be on the lookout for small banana-shaped growths in the buds. These “nanners” are pollen sacs and are a flashing red light that the plant is about to be pollinated.

Plants with bananas should immediately be removed from the grow (although it’s already too late if the nanners have opened). Growers are split on whether hermies can be saved if they’re caught early; some cut off the affected branches, but that stress can force the rest of the plant to turn hermaphrodite.

The best approach is to remove hermies from your grow room or garden as soon as you discover them. Keeping them isn’t worth the risk.

Early Signs of a Male Plant: FAQ

Q: Are there any other early signs that a plant is male or female?
A: Some growers swear they can sex plants by looking at the green hairs (stipules) near pre-flower sites, which supposedly are pointier and cross each other on female plants. That’s not a given, though; the much safer route is to look for differences in the pre-flowers. If you want to be positive and have a little extra money to spend, you can submit plant leaves for chemical testing and get definitive answers on plants’ sexes and future potency.

Q: Can’t hermies have sex organs on different parts of the plant?
A: Yes. These so-called “true hermaphrodites” are much less common than the “mixed gender” hermies we’ve discussed, but they do exist. It’s always a good idea to keep checking your “females” throughout the grow to be sure they don’t unexpectedly turn into hermies.

References

Leite Montalvão, A. P., Kersten, B., Fladung, M., & Müller, N. A. (2021). The diversity and dynamics of sex determination in dioecious plants. Frontiers in Plant Science, 2280 [1].

Punja, Z. K., & Holmes, J. E. (2020). Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences–impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science, 718 [2].

Chandra, S., Lata, H., & ElSohly, M. A. (2020). Propagation of Cannabis for clinical research: An approach towards a modern herbal medicinal products development. Frontiers in Plant Science, 11, 958 [3].

Luo, Y., Pan, B. Z., Li, L., Yang, C. X., & Xu, Z. F. (2020). Developmental basis for flower sex determination and effects of cytokinin on sex determination in Plukenetia volubilis (Euphorbiaceae). Plant Reproduction, 33(1), 21-34 [4].