What many growers don’t realize is that cannabis demands an uninterrupted dark cycle. Just as your good REM sleep would be interrupted if a light popped on at 2 a.m., cannabis doesn’t fare well when any light disturbs it during its dark “sleep” cycle. The moon and stars don’t bother cannabis, but any artificial light can stop its bud growth. In fact, light interrupting its dark cycles can make cannabis so stressed and irritable that it can lead to hermaphroditism. That can pollinate females and ruin your plants.
Cannabis growers know darkness is as important as light. You may not think of the principles of yin (dark) and yang (light) when planning your light deprivation schedule, but savvy growers understand the dual needs of cannabis. And whether your greenhouse sits in the Pacific Northwest under long summer days or in the hotter climes of the Central Valley, it’s essential to balance darkness and light for a maximum bud harvest.
Cannabis in the vegetative stage (when it is growing at a rapid pace) needs at least 13 hours of light per day. In fact, indoor growers commonly use an 18/6 light to dark ratio to encourage faster growth. (Note that most indoor growers vegetate their plants 4 – 8 weeks.)
Keep to Your Chosen Schedule
As a cultivated plant, cannabis still responds to light changes. Depending upon the strain you’re working with as well as your environmental demands, your light-to-dark ratio will vary a bit. If you’re new to the strain (or growing), talk to old hands about when to end the vegetative phase and trigger your plants’ flowering phase. That timing is critical to maximizing your yield. Here are some more specifics.
When you are ready for your cannabis plants to flower, a 12-hours of light and 12-hours of darkness schedule is standard. Nighttime provides darkness, keeping cannabis on somewhat of a natural clock. This is why indoor growers need to make a deliberate effort to not only create long, bright days but also emulate dark cycles for cannabis to grow large full buds.
If you decide on the classic 12/12 light dep schedule where you cover your plants at 7 p.m. and uncover them at 7 a.m., be consistent with that schedule. Keep in mind that this schedule requires adequate ventilation, so some growers will choose to uncover their plants at night once the sky is completely dark.
Why is Darkness So Important?
Cannabis is a photoperiodic plant that responds to seasonal changes in light. That means when the days grow shorter, the plant’s life cycle is nearing its end, and flowering occurs for reproduction. In nature, male cannabis sacs release pollen to pollinate female plants in blossom. The result is seeds, which allow the plant to produce the next generation.
Covering and uncovering your greenhouse on a set schedule, day in and day out can be extremely time and labor intensive. Pulling tarps is a lot of work, but using the right tools and products makes all the difference. To improve your harvest, you need to provide ample, reliable darkness for your cannabis, a good light deprivation cover and a tarp puller system will help you maintain your light deprivation schedule.
If a plant doesn’t get access to enough light at the surface, it stays in “root mode” and keeps growing taller without opening up its leaves
However, when it comes to red and far-red light as far as signals (not photosynthesis), it’s not the amount as much as the ratio of red to far-red that’s important to the plant! For the purposes of the plant and its response to light spectrum, red light is
There are new LED grow lights on the market that contain UVB, including this one which also contains light in the infrared spectrum. Although we know that UVB has an effect on cannabis, we don’t know exactly what changes, and whether it’s good, bad or a waste of time!
Plants keep track of days and nights using the ratio of red to far-red light
What if I can only pick one spectrum?
Blue light also has an effect on how stems and leaves tend to grow. Seedlings and plants given plenty of blue light tend to stay short, with short stems and squat growth. They tend to grow big leaves and spread them out.
Blue light also works together with red light to help the plant “know” whether it’s day or night time, and help set circadian rhythms. You may notice that cannabis plants start drooping right before the lights go off each day, and they start perking up right when lights come on. This is a way for the plant to save energy while it’s “sleeping.” Since the blue in the light helps it “know” the time schedule, it will prepare as best it can for lights-out and lights-on.
To grow cannabis successfully indoor, you need to mimic the natural growth pattern. When you grow your cannabis outdoor, they start to develop buds (flowers) as the days gets shorter, and they receive a minimum of 12 hours of complete darkness. To do this, just switch your light usage from 18 to 24 hours of good sunlight daily down to 12 hours of light and also of 12 hours of darkness for the cannabis life cycle.
For your plants to move from their vegetative stage to the flowering stage, they will need to be exposed to 12 or more hours of darkness each day to start flowering.
Also, it’s important to note that certain cannabis strains (like Northern Lights and Jack Herer, for example) grow higher yielding crops even without such manipulations.
Flowering Indoor Cannabis
Of course, the plants will not stop growing or developing flowers at this particular instance. On average, the plants start doubling up in height and shape after they begin the flowering stage — this is true for both indoor and outdoor plants. However, make sure your cannabis plants are NOT exposed to light during the 12 hours they are supposed to be in darkness. Take care: floodlights and even street lights can seriously disrupt the flowering period.
If you are growing your cannabis plant indoors and you do not have any issue with room height or space, then you should allow your plant to remain under 24/0 or 18/6 light schedule during the vegetative stage. This should last for 60 days, which is the best time to grow more flowers.
The Flowering Stage Light Cycle
Note that while in the vegetative stage, light is not the only means of growing large cannabis plants. If you are growing your plants indoors, you will need a well maintained grow room with a high ceiling.
Typically, most growers would start their cannabis plants indoors under lights before moving them outside to grow under the sun. Most growers would usually start either cutting clones or starting seeds during March or April, and would keep them under 18 to 24 hours of constant light before moving them outside in the early period of May or June.