Cannabis is a short day plant. That’s because the dark cycle dictates the pace of growth for photoperiod marijuana. There are thousands of blogs about lighting and a dearth concerning the dark cycle; so we’ve gone Darth Vader and invite you to join us on the dark side of sinsemilla.
When cannabis plants, like other green plants, are in the light—be it sunlight or artificial light—they are photosynthesising. This is how they convert light into energy and release oxygen. They are also respiring. That’s right, contrary to the misinformation circulating elsewhere, plants, like all other aerobic organisms, are respiring all the time. We stop when we die, and we die if we stop. Cannabis plants are just producing a surplus of oxygen during the daytime.
Only autoflowering seeds have a predetermined post-germination life cycle. The autoflowering trait is believed to be an adaptation to the almost continuous 24 hours of sunlight unique to Siberia. True autoflowering varieties will start to bloom after about 30 days of vegetative growth.
Currently trending is the new 6-2 alternative vegetative growth lighting schedule. Three of these light-dark cycles per 24-hour period means the cannabis plant receives the same total 18 hours of light and 6 hours of darkness as a conventional 18-6. Moreover, this is a viable option as photoperiod cannabis needs a continuous 12 hours of darkness to bloom. The thinking being, those brief 2-hour intervals of darkness give the plant a chance to rest and process CO₂ more effectively. Also, 6-2 avoids light saturation and is potentially a more effective light-dark cycle for photosynthesis.
Grow tents and grow rooms need to be checked for cracks and tears. Greenhouses can be covered to make sure nighttime is completely dark as long as it needs to be. It doesn’t take much to patch a hole or buy a light-proof tarp. But interruptions to the dark cycle during flowering could cost you a whole harvest.
Photoperiod cannabis is sensitive to changes in the hours of daylight it receives. In fact, photoperiod cannabis strains cannot transition from vegetative growth to flowering without long nights. 12 or more hours of darkness is the biological trigger for photoperiod cannabis to bloom. Outdoors, as the nights grow longer incrementally from the summer solstice onward, some strains can even begin flowering when receiving 14 hours of sunlight.
Photoperiod cannabis strains can essentially be kept in vegetative growth indefinitely, so long as they receive 14+ hours of light per day. The debate on what is the optimal light-dark schedule for vegging cannabis rages on. That being said, most indoor growers will agree that somewhere between 18–24 hours per day is perfect. Outdoor growers get started in spring/summer to make the most of the long days too.
The 24-0 schedule might speed up the vegetative growth process some. The downside is the higher power bills. 18-6 is more common because it’s a closer match for long summer days and a little cheaper. Higher success rates with cuttings on an 18-6 light-dark cycle than those receiving 24-0 is the only substantial difference we have discovered from our own experiments.
Interruptions to sunlight come in the form of clouds. Cannabis plants can handle this. But anything short of a pitch black dark cycle with no light pollution for the duration will suffice for photoperiod strains. Light leaking into the grow-op when the grow lights are off will stress plants and disrupt flowering. This can stress a female plant into an intersex plant. Street lighting can confuse outdoor photoperiod cannabis plants and prevent them from flowering. Only a green bulb can be used if you must tend to plants or enter the garden during the dark cycle.
The dark cycle is just as important as the light cycle. In this blog, we discuss what happens to cannabis when the lights are off.
Growing with a 12-12 photoperiod is a solution to space and resource problems. This method eliminates the vegetation phase of growth and forces the plant to go straight into flower from a seedling. Yields are lower than that of a regularly grown cannabis plant, but results are obtained much faster, with a few advantages.
There is a lesser demand for resources across the boards.
There are some haters of this method, but many love it. Those who hate on it often have not actually tried it. It is all about giving it a go and seeing what works for you. Even if you decide against it after trying it, it all helps expand your knowledge as a grower.
Growing this way still requires all the knowledge that would be needed to flower plants with any other method, and maintenance routines still remain unchanged. After diluted nutrients, while still young, treat your plants as you would during a normal bud cycle. However, flush more often, every ten days at most, so as to avoid salt build-up in the smaller pots.
Growing 12-12 is as simple as changing the timing on your light cycles, giving your plants equal amounts of day and night right from when they sprout. The plants will look different to a cannabis plant that goes through vegetative growth. Photosensitive hormones in cannabis make the highest point the largest cola. This method all but guarantees only main bud growth on every small plant. Essentially you will be growing a cola with a few short, budded side branches – with the plant basically being a bud in itself. Be sure to stake your plants.
12-12 simply refers to the hours of light and darkness a cannabis plant is exposed to – 12 of each. Normally, a cannabis plant is exposed to an 18-6 light cycle. This tells the cannabis plant conditions are good for growth, and it focuses on building up size and foliage. When light cycle is changed to 12-12 (either naturally or through human intervention), it tells the cannabis the seasons are changing, and it is time to flower. By forcing a 12-12 light period from the start, the cannabis plant goes directly into flowering, in a bid to reproduce. You are essentially tricking the plant into thinking the growing season is coming to an end, so it needs to produce flowers ASAP.
Everything to which you would pay attention in a normal grow remains unchanged and are still just as important. pH and water quality, nutrient mixing, pest control, grow medium conditions, EC and ppm all still play their major roles in the dankness and weight of your finished product.
Plants with less side branching and canopy spread need less space between them, increasing efficiency. As an example: 1x 15-litre pot produces one plant with a large volume and difficult maintenance issues in a cramped space. 4x 3.5-litre pots in the same sized space can produce just as much dried material with the benefit of being easier to rotate, so the whole plant gets 360-degree light. The entire crop is less hassle during maintenance as each plant is 100% accessible and physically easier to move about. There is no need for a separate sprouting and veg space or time wasted on 18-6 vegetation. The seeds can be sprouted under the 12-12 growing lights providing continual flowering plants.
You will experience only half the water consumption with less moisture loss due to evaporation, and a third less nutrients are used. CO₂ and electricity use including most peripherals are reduced by a staggering 650 grow hours annually.
How to force cannabis to flower from seed for quick, resinous yields using a 12-12 light cycle.