Marijuana plant anatomy and physiology

The cannabis plant has several structures, many of which we can find on any ordinary flowering plant species. Cannabis grows on long skinny stems with its large, iconic fan leaves extending out from areas called nodes.

Cannabis really stands out in its flowers—or buds—where unique and intricate formations occur: fiery orange hairs, sugary crystals, and chunky buds enveloped by tiny leaves.

Cannabis is a dioecious plant, meaning it can be male or female, and the male and female reproductive organs appear on different plants. What’s in your stash jar now are the flowers of a female marijuana plant.

Female plants produce the resin-secreting flower that is trimmed down into the buds you smoke, and males produce pollen sacs near the base of the leaves. Male plants pollinate females to initiate seed production, but the buds we consume come from seedless female plants—these are called “sinsemilla,” meaning “seedless.” 

Growers can ensure the sex of their plants by growing clones or the genetically identical clippings from a parent strain. Feminized seeds are also made available through a special breeding process.

Female marijuana plants

Females are the prizes of cannabis plants—they are the ones that grow the buds that we all know and love. Anytime you see a picture of a cannabis plant with buds, you are looking at a female plant.

Female cannabis plants receive pollen from males to produce seeds, which will carry on the genetics of both plants to the next generation.

However, cannabis is primarily cultivated for buds, not seeds, so the practice of growing sinsemilla, or “seedless” cannabis, is prevalent today: Females and males are grown separately, or males are even discarded, to prevent pollination. This allows female plants to focus their energies on bud production instead of seed production.

Males and females are usually only pollinated when crossbreeding plants or creating new strains.

Male marijuana plants

Male cannabis plants grow pollen sacs instead of buds. Male plants are usually discarded because you don’t want them to pollinate the females, which will produce seeds—no one wants to smoke buds with seeds in it. 

Males are important in the breeding process, but that is generally best left to expert breeders. When pollinating females, males provide half of the genetic makeup inherited by seeds.

Because of this, it’s important to look into the genetics of the male plants. Their shape, rate of growth, pest and mold resistance, and climate resilience can all be passed on to increase the quality of future generations.

Male plants can also be used for:

• Hemp fiber—males produce a softer material, while females produce a coarser, stronger fiber. The soft fiber from males is more desirable for products like clothing, tablecloths, and other household items.
• Concentrate production—males do have some THC and can be psychoactive, but much less so than females. Small amounts of cannabinoids can be found in the leaves, stems, and sacs, which can be extracted to produce hash and other oils.

PRO TIPS FOR A BETTER HARVEST

Guiding cannabis plants through their flowering phase can be intimidating, especially for rookie growers. Follow these simple tips to ensure you always end up with a great harvest:

• Most growers identify the sex of their plants in the final week of vegging or the early weeks of flowering. Remember, males develop pollen sacs that look like small balls, and need to be culled or separated from your females if you want to avoid them getting pollinated. Also, keep an eye on your female plants as they flower to catch any hermaphrodites. While it’s not common, some cannabis plants may develop both female and male flowers, while others may develop stamen (colloquially known as “bananas”) as a final attempt to create seeds in response to heavy stress.
• If you’re an indoor grower, you have the advantage of controlling when your plants start to flower. Make sure to use this to your advantage and only ever flip your plants to flowering when they’re 100% healthy. You don’t want to be correcting nutrient deficiencies or fighting pests and diseases while your plants are budding. If you’re growing outdoors, you have less control over when your plants start to flower. Instead, you’ll want to pay close attention to the calendar and fix any issues before the end of summer.
• Flowering plants require different humidity levels and temperatures than vegging plants. Rather than changing the temperature, humidity, and light cycle at the same time, we recommend gradually changing the temperature and humidity over two days, then letting your plants grow accustomed to these changes by leaving them in veg for just a few extra days before flipping your lights.
• Before flowering, make sure to train and trim your cannabis plants a bit to allow as much light as possible to reach its bud sites. Now, every grower has their own approach to trimming, but we like Kyle Kushman’s recommendation: “If the tip of a branch doesn’t break at least 50% of the height of the plant, it’s gone”. The idea here is to help your plant concentrate its energy only on the bud sites that’ll produce the best product.
• Also, remember to always trim yellow or dead foliage during flowering. While your plants should stay lush and green up until about week four, some of their foliage will stop thriving as they devote more energy to bud production. This is completely normal, and you can safely remove any leaves that turn yellow or dry out completely.

Flowering cannabis plants like daytime temperatures of 20–23°C and nighttime temperatures of around 15–18°C. Make sure to watch out for sudden drops or spikes in temperature when you turn your lights on/off. Sudden drops can shock your plants, while sudden rises can cause condensation to form on the surfaces of your buds, leading to bud rot.

Supplementing with CO₂ during the bloom phase can enhance growth and yield. If you can, aim to keep CO₂ levels at 1,000–1,200ppm during flowering.

You can’t compensate for nutrient burn during flowering. Make sure to follow a strict feeding calendar and remember to stop feeding two weeks before harvest and flush your plants.