I have grown many Cannabis males to maturity to collect and freeze pollen, as well as to use them to pollinate females for cross breeding and seed production. I have also had females herm (hermaphrodites that are females that produce some male flowers) on me in large grows. Contrary to popular opinion, it is not the end of the world if you get males, or herms, or god forbid, seeds!
Sexing Cannabis plants can be difficult. Also they can flip sex on you, even if you have fem seeds or female cuttings. So you have to be observant of your plants. The best way to tell the difference is that the females will have a pair of fine white calyxes extending from their flowers, and males will not. Males will develop pods, or 'bananas', usually in clusters that will then hang from small stems. These flowers will then pop open and after a day or so the pollen will ripen and fall off. If you see any fluffy yellow pollen on the leaves of the male, that will have happened. One tiny male flower will have thousands of pollen granules which is enough to pollinate an entire female plant! So beware...
Males will only pollinate ripe and ready female flowers that the pollen comes into contact with. If the females are not flowering and ready to be pollinated, they will not be affected. Pollen is only viable for a few days at most. After that it dies. So pollen will not fertilize females flowers that open a week or more later. Males tend to mature earlier than females, so generally they can be spotted and pulled or removed before the females flower. If some females are pollinated, you will likely get some seeds, but only in the flower stems that are pollinated will the levels of THC drop. It will not affect the whole plant unless it is completely pollinated. Even if your females are pollinated and go to seed, all is not lost. We smoked weed for several millennia with seeds and got high. I also smoke male flowers to get high. Yes, they have THC in them, contrary to popular belief.
As to why some females flip to become males? Generally sex in Cannabis plants is determined when a seed is created after a female ovum is pollinated. However, that can be changed due to environmental and genetic factors. If you are growing from non-fem 'standard' seeds, you will get about a 50/50 male to female ratio of plants, so it is normal to get about half males and half females. If you are growing from fem seeds, you will likely still get a small number of males, even in ideal conditions (no matter what the seed company guarantees!). Generally the problem with fem seeds is that you are likely to get herms for genetic reasons. Herms tend to beget more herms. If you are growing from female cuttings (or fem seeds), you can still get them to flip sex to being males, or herms. The Dutch have done a lot of research on this and it seems to come down to a variety of stresses that can force females to turn male. Too much heat, too little water, variations in pH, changes in lighting, etc. can all affect and flip them. There are also chemicals that can flip females to males, as well as males to females. But they are not so easy to get ahold of.
Happy growing...
Sexing Cannabis plants can be difficult. Also they can flip sex on you, even if you have fem seeds or female cuttings. So you have to be observant of your plants. The best way to tell the difference is that the females will have a pair of fine white calyxes extending from their flowers, and males will not. Males will develop pods, or 'bananas', usually in clusters that will then hang from small stems. These flowers will then pop open and after a day or so the pollen will ripen and fall off. If you see any fluffy yellow pollen on the leaves of the male, that will have happened. One tiny male flower will have thousands of pollen granules which is enough to pollinate an entire female plant! So beware...
Males will only pollinate ripe and ready female flowers that the pollen comes into contact with. If the females are not flowering and ready to be pollinated, they will not be affected. Pollen is only viable for a few days at most. After that it dies. So pollen will not fertilize females flowers that open a week or more later. Males tend to mature earlier than females, so generally they can be spotted and pulled or removed before the females flower. If some females are pollinated, you will likely get some seeds, but only in the flower stems that are pollinated will the levels of THC drop. It will not affect the whole plant unless it is completely pollinated. Even if your females are pollinated and go to seed, all is not lost. We smoked weed for several millennia with seeds and got high. I also smoke male flowers to get high. Yes, they have THC in them, contrary to popular belief.
As to why some females flip to become males? Generally sex in Cannabis plants is determined when a seed is created after a female ovum is pollinated. However, that can be changed due to environmental and genetic factors. If you are growing from non-fem 'standard' seeds, you will get about a 50/50 male to female ratio of plants, so it is normal to get about half males and half females. If you are growing from fem seeds, you will likely still get a small number of males, even in ideal conditions (no matter what the seed company guarantees!). Generally the problem with fem seeds is that you are likely to get herms for genetic reasons. Herms tend to beget more herms. If you are growing from female cuttings (or fem seeds), you can still get them to flip sex to being males, or herms. The Dutch have done a lot of research on this and it seems to come down to a variety of stresses that can force females to turn male. Too much heat, too little water, variations in pH, changes in lighting, etc. can all affect and flip them. There are also chemicals that can flip females to males, as well as males to females. But they are not so easy to get ahold of.
Happy growing... 
