How to Sex Cannabis Plants: Reading Male and Female Pre-Flowers

To sex a cannabis plant, look at the pre-flowers that form at the nodes, where branches meet the main stem: males grow smooth little balls (pollen sacs), while females grow teardrop-shaped calyxes with fine white hairs (pistils). Plants that show both are hermaphrodites. Learning to spot all three is key to a successful grow, especially if you're a beginner, you're planning to breed strains, or you want to maximize the harvest from your female plants.

Getting to know the cannabis plant

Cannabis belongs to a small minority of plant species known as dioecious, which means individual plants are either male or female.

Male and female cannabis plants look identical during the seedling and vegetative stages. But once they start flowering, they reveal their sex. During flowering, females produce resinous buds loaded with cannabinoids, while males start producing little sacs full of pollen.

Female cannabis plants: why everyone wants them

Female plants are the main target for anyone growing just for personal use. That said, depending on their genetics, female plants can look very different from one another. Some stay small, with a dense canopy and plenty of side branches, while others top 3 m (10 ft), can produce massive harvests and look more like a tree than a regular garden plant.

But whatever their differences, all female plants have one thing in common: they produce female flowers. These flowers, commonly known as buds, are covered in tiny glandular structures called trichomes, which is where cannabinoids like THC and CBD are made.

Male plants, on the other hand, don't make female flowers. They make male flowers instead, which is why they're less valuable to growers who only want buds. Male flowers produce small pollen sacs that carry the genetic material needed to fertilize female flowers and make seeds. That makes males extremely important for breeding new cannabis strains.

What about male cannabis plants?

When it comes to male plants, keep in mind that male pollen sacs and female flowers develop in the same part of the plant. Both sprout from the nodes (where the branches meet the main stem). So when you notice some plants starting to form buds, the smart move, for the good of your whole grow, is to go looking for pollen sacs.

Hermaphrodite cannabis plants: what are they?

Cannabis plants need a certain amount of care, and even when you give yours all the love it needs, it doesn't always play by the rules of nature. Sometimes this dioecious species goes against the grain and develops both male and female reproductive organs on the same plant. These are known as hermaphrodites, or hermies. But why does it happen?

It's an unusual trait that can be caused by genetics, environment or both. Hermaphrodite plants produce both buds and pollen sacs, so they can pollinate and fertilize themselves.

Needless to say, if you want the best buds possible, you'll want to avoid this.

When can you tell if your plant is male or female?

Lucky for beginners, male pre-flowers show their telltale features before female ones do. That lets growers pull male plants out of the grow space well before the females start flowering. It's very common for males to reveal their sex about two weeks before females, with pre-flowers often showing up around the sixth week of the grow cycle.

How to identify male cannabis plants

First, to sex your plants, you need to find the pre-flowers, which, as we mentioned, are tiny structures that form at the nodes toward the end of the vegetative stage.

Once flowering starts, check your plants with a magnifying glass. Inspect a few nodes on each plant to see where they are in the flowering process. At this point you probably won't see any female flowers or pollen sacs yet. This is when you want to look for young pre-flowers, male or female: tiny structures that look alike at first glance but have unique features that set them apart.

Male pre-flowers are little balls that look like tiny green eggs: smooth, with no hairs or other distinctive marks. As flowering goes on, these sacs form bigger, denser clusters, and by then they're easy to spot with the naked eye. In general, pollen sacs start releasing their contents about 2-3 weeks after they form, so it's best to remove males as soon as you can.

How to identify female cannabis plants

Female pre-flowers also form at the nodes, and you can tell them apart by one very obvious feature: hairs. Female pre-flowers produce teardrop-shaped calyxes with fine hairs sticking out of the tip. These little hairs are called pistils, and they're the sexual organs of female cannabis flowers.

Pistils are designed to catch pollen so the flowers can be fertilized. They stick out of the flowers to grab pollen drifting through the air (cannabis is mainly wind-pollinated) or brushed on by pollen-covered insects.

Within a few weeks, these tiny pre-flowers swell into dense buds that start pumping out resin rich in cannabinoids and terpenes. If you've removed the males properly to prevent pollination, your female flowers will keep producing resin right up to the end of the grow cycle.