Unfortunately, about 50% of all regular (unfeminized) cannabis seeds are male (though this varies from strain to strain, and from environment to environment). Fortunately for small growers, you can purchase feminized (all-female) seeds so you don't have to worry about male plants if you don't want to. Learn more about buying seeds.
For an indoor grower, when a plant is about half the final size you want it to be, you should change it over to the "Flowering" stage. This is the stage when your plant starts growing buds.
In the wild, as the days get shorter and nights grow longer, a marijuana plant "realizes" that winter is coming and will start budding/flowering. It "knows" it's approaching the end of its life cycle so it frantically starts making buds in time before winter.
If you're growing a cannabis plant grown from a random seed ("bagseed"), unless you somehow have an auto-flowering seed, you will need to understand about cannabis life stages and how they are affected by light periods.
Marijuana plants have an internal process that allows them to detect how long they receive darkness each night. This is because they are a "photo-period" plant, specifically a "short-day" plant which means these plants start making flowers/buds when days start getting short.
Outdoor growers plant their seeds in Spring when the days are naturally longer. In the wild, cannabis seeds naturally germinate in the Spring.
I tend to set my timer to shine line from 8pm-8am. This gives me time to check on my plants at night when the lights first come on, and I can also check them quickly in the morning before I go to work. It also keeps things cooler since the lights go on at night.
This isn’t to say your plant will stop growing and only produce flower at this point. On average, plants will double in height after the begin the flowering stage both indoors and out. When growing outdoors, however, it’s extremely important plants aren’t exposed to light during the 12 hours they’re supposed to be in darkness. Even streetlights or floodlights can disrupt the flowering period. So, if you’ve got that neighbor who leaves on a floodlight all night that shines on your plants, you might want to see if they’d be willing to put it on a sensor.
If you’re growing outdoors, keep them inside on an 18/6 or 24/0 light schedule until all danger of frost and freezing temperatures are over and you can safely take them outside. Once they’re outside all you need to do is let nature do its thing as the sun rises and sets each day on its own.
When growing indoors, growers will typically put plants on a schedule of 12 hours of light and 12 hours of darkness (12/12) once plants have reached the desired size during the vegetative period. On average, growers veg indoor plants for 4-8 weeks under an 18/6 or 24/0 light period.
It’s important to keep in mind however that it’s not just your light schedule during veg that will ensure a bigger yield come harvest. Some strains, such as Jack Herer and Northern Lights , simply produce more weed. And if you’re growing inside and don’t have high ceilings and a well-maintained grow room, your plants aren’t likely to get as big as you’d like them to be. Big plants with big yields need plenty of space to grow.
Light Cycle for Outdoor Flowering Period
The key to growing indoor cannabis is mimicking what happens in nature. When grown outdoors, cannabis starts to produce flowers (buds) when the days begin to become shorter and they receive at least 12 hours of total darkness. All that’s needed to do this is to switch your light schedule from 18-24 hours of “sunlight” each day to 12 hours of light and 12 hours of darkness.
Being able to manipulate a plant’s light schedule makes it possible to achieve higher yields when it comes time to harvest. When plants are in the vegetative stage, the more light they receive the larger they will grow.
Whether you’re planning on growing indoors or outdoors, knowing the best light schedule to follow will help maximize your yield in the end. If you’re growing inside and height and space are not a big issue, letting your plants stay in the vegetative stage on an 18/6 or 24/0 light schedule for at least 60 days (8 weeks) is your best bet to grow the most bud.
Light Cycle for Indoor Flowering Period
If you are growing outdoors , it’s vital you keep your plants inside until all danger of freezing temperatures is over. The last thing you want is for a late-spring snowstorm or sudden drop to freezing temperature to kill your plants. Once all danger of a cold snap has passed, plants will remain in veg outdoors from late spring until late summer.
That being said, they also need plenty of light to reach their maximum potential. This is why some growers give their plants 24 hours of light each day. Stick with 18-24 hours of light during the vegetative stage and your plants will reach their maximum potential before it’s time to manipulate the light schedule to make them flower.