Cannabis plants are dioecious, meaning they typically develop as either male or female individuals. “Sexing” is the act of identifying the plant’s gender at an early stage to determine its role in cultivation. Most growers aim to isolate the female plants, which produce the cannabinoid-rich flower or bud, and remove the males. Male plants generate pollen sacs that, if allowed to mature, will fertilize the female flowers, causing them to produce seeds instead of potent, seedless buds (sinsemilla).
Timing the Reveal
Cannabis plants begin to reveal their sex during the pre-flowering phase, the intermediate period between the vegetative stage and full flowering. For indoor photoperiod strains, this transition is intentionally triggered by changing the light schedule to 12 hours of light and 12 hours of uninterrupted darkness. This shift in the photoperiod mimics the shorter days of late summer and autumn, signaling the plant to reproduce. The first visual signs of gender, called pre-flowers, typically appear at the plant’s nodes within one to three weeks after this light cycle change has been initiated. Male plants often display pre-flowers slightly earlier, sometimes showing signs as early as three to four weeks from germination, while female pre-flowers usually emerge between four and eight weeks.
Recognizing Male Pre-Flowers
The male pre-flower is designed to hold and release pollen, giving it a distinctive, easily identifiable appearance. These structures emerge at the nodes, the junctions where the leaf stems and side branches meet the main stalk. The male pre-flower appears as a small, smooth, ball-like sac, often resembling a tiny grape or olive atop a short stalk. These pollen sacs may appear individually at first, but they often develop in small, tight clusters as the plant matures. Growers sometimes describe the early shape as a small, round bulb lacking any extending hairs. Inspect the upper nodes, as pre-flowers tend to appear there first.
The moment a male pre-flower is identified, the plant must be immediately removed from the growing area to prevent accidental pollination. A single male plant can release enough pollen to contaminate an entire crop, causing female plants to produce seeds. Removing males ensures the remaining female plants focus their resources entirely on developing resinous, unpollinated flowers.
Recognizing Female Pre-Flowers
Female pre-flowers signify a bud-producing plant, which is the desired outcome for most growers. Like male structures, these pre-flowers emerge at the nodes along the main stem and branches. The female pre-flower is a small, teardrop or pear-shaped structure. This structure is a small calyx, and the definitive sign of a female plant is the emergence of one or two fine, wispy hairs from the tip.
These hairs are technically called stigmas, though they are commonly referred to as pistils. The stigmas are typically white or transparent and are the receptive organs meant to catch airborne pollen. The presence of these delicate pistils confirms the plant is female and should be retained to produce dense, cannabinoid-rich flowers.
What to Do About Hermaphroditism
Hermaphroditism, often called “hermie,” occurs when a single cannabis plant develops both male pollen sacs and female pistils. This condition can be caused by either a genetic predisposition within the strain or severe environmental stress. Common stressors that can trigger this response include light leaks during the dark period, extreme temperature fluctuations, or nutrient imbalances.
Growers must vigilantly inspect female plants, particularly during the middle to late flowering stage, for any unusual male structures. One visual sign is the emergence of small, yellow or pale green, banana-like growths, which are exposed stamens, colloquially called “nanners.” These stamens can shed pollen immediately upon emergence, making them a serious threat to the crop. If only a few male parts are found, they can sometimes be carefully removed with tweezers before they release pollen. However, if the plant shows widespread male flower development, it is safest to immediately remove and discard the entire plant to prevent seeding the rest of the garden.