There’s no real consensus on whether autos grow better under 18 or 24 hours of light, and we’ve seen growers achieve great results with both methods. To make up your mind, we recommend playing around with both variations and sticking to what works best for you.
Cannabis is a C3 plant, meaning it can absorb CO₂ for photosynthesis even during light hours. And since autoflowering plants have short vegetative phases and often grow shorter than photoperiod strains, you’ll typically want to give your autos at least 18 hours of light. This allows for robust growth, without overspending on energy. Your autos love light just as much as traditional photoperiod strains, they just don’t rely on it to begin bloom.
SOG is a great technique to try with autos because it takes advantage of the naturally smaller stature of these varieties. While every grower will have their own technique for SOG, most will grow between 4–16 plants per m², depending on how big they let each plant grow.
Growing autoflowering strains? In this article, we explore the ideal light schedule to help your autos produce the best possible harvests.
SOG, or sea of green, is a cannabis training technique that can produce some great harvests. Rather than getting your plants to grow as large as possible, SOG involves growing several smaller plants in close proximity to form a uniform canopy that maximises light exposure and space.
- 6500K blue light during veg: Blue light spectrums have been shown to encourage vegetative growth, helping cannabis plants grow short and stocky while minimising stretching.
- 2700K red light during flowering: Red light spectrums are ideal for bloom because they encourage budding and a little bit of stretch, encouraging your plants to produce big, dense flowers.
Some growers will even give their autos a full 24 hours of light, arguing that this helps maximise vegetative growth. Growers who stick to 18-hour light cycles, on the other hand, argue that this gives their plants a short “recovery” period that is essential for healthy growth.
Depending on the size of the particular strain you’re growing, we recommend using 7–10l pots and growing between 4–6 plants per m². This should make the most of your space and lighting while still providing your plants with enough airflow to avoid any mould issues. If you decide to grow more plants per m², remember to use smaller pots to control their size and avoid overcrowding your grow room.
As you might recall from science class, when you shine a light through a prism, it is broken up into different colour spectrums. Plants, which depend on light for photosynthesis, respond differently to these different spectrums. Like with a photoperiod cannabis strain, we recommend sticking to the following light spectrums:
Growing autos? Click here to learn all you need to know about the right light schedule for autoflowering cannabis strains.
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.
During the dark cycle, cannabis plants are not photosynthesising, and continue to respire at a constant rate; they do not just begin to respire when the lights go out. The Calvin Cycle, which is light-independent, processes all that stored up solar energy into carbohydrates. Roots are also respiring, so it’s very important to grow in well-aerated substrates. Take advantage of air pots to keep your medium oxygen-rich.
However, even if you grow a photoperiod strain from seed with a 12-12 schedule, it will take 3–4 weeks before buds begin to develop. Photoperiod cannabis is an annual plant. Marijuana can survive with as few as 8 hours per day, and flowering photoperiod plants can even be re-vegged. The switch can really be flipped back to vegetative growth with the resumption of longer days.
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.
12-12, the even split of 12 hours of light and 12 hours of darkness, only occurs naturally close to the equator. Indoor growers rely on timers to artificially dial in this light-dark cycle. During the day or lights-on period, two receptors, phytochrome red and phytochrome far-red, are in balance. In darkness, the far-red change into red. It’s the increase in red that triggers flowering. Many growers leave plants in complete darkness for 36 hours before commencing 12-12 to ensure a high phytochrome red ratio.
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.
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.
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.
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.