The Perfect Light Schedules For Autoflowering Cannabis
Growing autoflowering strains? In this article, we explore the ideal light schedule to help your autos produce the best possible harvests.
WHAT’S THE BEST LIGHT SCHEDULE FOR AUTOFLOWERING CANNABIS?
Autoflowering cannabis strains flower based on age, rather than a change to their light cycle. Nonetheless, providing your autos with the right amount of light remains crucial to ensuring the best possible harvest. Read on to learn all there is to know about lighting for autoflowering cannabis strains.
18/6 LIGHT CYCLE
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.
24HR LIGHT CYCLE
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.
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.
WHAT ABOUT A 12/12 LIGHT CYCLE?
Some growers still decide to keep their autos under a 12/12 light cycle during flowering. And that’s fine, as autos grown in these conditions can still produce a fair harvest. Just remember that the buds you harvest under a 12hr light cycle will be noticeably smaller than what you’d get under a 18–24hr cycle. Some reasons you might consider keeping your autos under 12/12 include:
- Heat concerns: If you live in a very hot climate, you might want to turn your grow lights off during the day to avoid overheating your grow room. In that case, growing your autos under a 12/12 light cycle—with lights on during the night—might be your best bet to avoid causing your plants heat stress.
- Growing autos alongside photoperiod strains: If you’re growing autos alongside feminized photoperiod strains, you’ll likely have to place your autos in the same room as your flowering feminized plants, meaning your autos will only get 12 hours of light per day.
- To save money: Running grow lights for 18–24 hours over a few months can get very expensive. If you want to grow autos on a tight budget, you might want to use a 12hr light cycle instead.
PERFORMING SOG WITH AUTOFLOWERS
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.
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.
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.
A NOTE ON LIGHT SPECTRUM
Using the right light spectrum is super important when growing any type of cannabis plant, including autos. Because autoflowering plants have such short life cycles, you really want to maximise the quality of light, nutrients, and soil you give them.
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:
- 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.
EXTRA TIPS FOR GROWING GREAT AUTOS
If you’re new to the world of autoflowers, follow these simple tips for a better harvest:
- Pick a high-yielding auto: Not all autoflowers are made equal, so be sure to pick a high-yielding strain if harvest size is important to you.
- Plant in your final container: Up-potting cannabis plants always causes stress. Since autoflowers can go from seed to harvest in as little as 8 weeks, it’s best to avoid this kind of stress and always plant your seeds straight into their final pots.
- Use an airy growing medium: This helps stimulate root and foliage growth.
- Use LST: If you want to train your autoflowering cannabis plants, only use low-stress techniques. High-stress techniques like fimming, topping, and supercropping will end up doing more harm than good.
Growing autos? Click here to learn all you need to know about the right light schedule for autoflowering cannabis strains.
Is 12-12 From Seed Worth It?
Will 12/12 from seed give you huge yields? In a word, no… but there are benefits to initiating the flowering stage as soon as possible. Giving a 12/12 light schedule from seed is a great way to create tiny “bud stick” plants, which may be perfect for a small stealthy garden. When modified slightly, the same basic technique can create bigger plants and bigger yields while adding little to no extra time before harvest. And then there is the matter of genetics. Certain strains give better results than others.
The “12 /12 from seed” technique aims to initiate the flowering stage immediately after germination. Learn about cannabis light schedules.
This creates small “bud stick” plants that are typically ready to harvest in 3-4 months. Check out this beautiful example of “12/12 from seed” by Fuel.
If you haven’t heard this term before, “12/12 from seed” means giving your cannabis seedling 12 hours of light and 12 hours of dark each day from the moment of germination. Providing a 12/12 light schedule initiates the flowering stage and causes cannabis plants to start making buds. The idea of this technique is to get seedlings to start flowering as quickly as possible to reduce the time to harvest. Once a plant has started flowering, most strains are ready to harvest within 12 weeks. The sooner you get a plant to start flowering, the sooner you get to harvest.
There’s just one major problem… 12/12 from seed often causes stunted growth and small yields. This results in yields that are often less than 1 ounce per plant, even under strong grow lights.
This seedling took nearly 4 months from seed to harvest under about 150W of fluorescent lights and yielded only 1/2 of an ounce.
I think it looks kind of cool, but 1/2 ounces is not a great harvest after waiting so long. I’ve found you can tweak the light schedule to double or triple your total yield per plant without necessarily increasing time-to-harvest or plant height. More on that below!
12/12 from Seed – What You Need to Know
Something that’s a bit confusing about 12/12 from seed is it seems like seedlings should start flowering immediately. They don’t. I’ve found that photoperiod seedlings won’t start flowering until they’re 3-4 weeks old no matter the light schedule. That means your harvest won’t come any sooner if you initiate 12/12 before seedlings are 3 weeks old. When you give the plant 3-4 weeks of 18+ hours a day, THEN switch to 12/12, you often get better results because plants are quite bigger when buds start forming, without adding much (if any) time to harvest.
Most seedlings won’t make buds until they’re at least 3 weeks old from germination. There’s nothing you could do to get this little seedling to start flowering.
You often get better yields by giving plants 18+ hours of light a day for the first 3-4 weeks. These plants got 18/6 until they reached this size.
I started the 12/12 light schedule right after the above picture. They ended up yielding a lot more than my plants that were given 12/12 from seed in the same setup. Yet they didn’t get much taller or take longer to harvest.
Here are those same plants a month later after they started making buds (plants double or triple in height after the switch to 12/12, especially young plants)
A few weeks of extra light, in the beginning, seems to achieve plants with longer and fatter buds (why was this plant defoliated?)
Plants reward you for giving them a little more time to grow. For example, a solid 4 weeks of 18/6 before 12/12 creates plants that are ready to harvest around the same time as a plant given 12/12 from seed (3-4 months, depending on the strain), but significantly bigger yields.
If you’re worried about plants getting too big, you can gain complete control of plant shape by topping and bending plants to stay flat when they’re young. This increases the amount of bud produced without raising the overall height.
Many people who give 12/12 from seed have chosen this technique to ensure plants stay as small as possible. That’s why it’s common to see these plants in very small pots (like solo cups). Just like with bonsai trees, restricting root space is an effective way to reduce overall plant size. Plants kept in solo cups rarely get bigger than one long bud stick, especially when given 12/12 from seed.
Restricting root size reduces plant size dramatically, especially when combined with 12/12 from seed. Look how big this plant is in relation to the lighter!
12/12 From Clone – When You Want TINY Plants
If you want to grow the absolute smallest plant possible, “12/12 from clone” may be a better choice than 12/12 from seed. A clone is a piece of a bigger plant that was removed and forced to grow roots. Since a clone is technically the same “age” as its mother plant, it’s pretty much a mini mature plant as opposed to a seedling. Because they’re already mature, clones start flowering almost immediately after getting 12/12. That can result in some REALLY small plants at harvest.
Unlike seedlings, clones will start flowering almost immediately after getting 12/12. If you start with small clones in miniature pots, you end up with short buds on sticks at harvest.
These “12/12 from clone” plants are cute and fun! Though not necessarily the most productive when it comes to actual yields.
Auto-Flowering Strains – When Time is of the Essence
Some growers want to use 12/12 from seed to get to harvest as soon as possible, but it’s not actually the best option for a quick harvest. If you’d like to be able to harvest plants even sooner than 3 months, consider giving autoflowering plants a try. Most autoflowering strains are ready to harvest just 2-3 months from germination. That’s less time than almost any photoperiod plant will take, no matter what light schedule you provide. Even better, autoflowering plants on average yield 1-2 ounces each (more if you care for them well), which is better yields than most “12/12 from seed” plants.
The “modern” version of 12/12 from seed is simply using an autoflowering strain. They don’t need special light schedules and are ready to harvest in just 2-3 months from germination.
Autoflowering plants are typically given 18-24 hours of light a day their whole life, which allows them to get bigger in less time than plants under a 12/12 schedule.
Auto-flowering strains are ready in 2-3 months from seed, and yield an average of 1-2 ounces/plant. You can yield even more with low stress training (LST) and great care.
Use “Sea of Green” (SoG) to Maximize Photoperiod Yields
If you want to grow photoperiod strains (or can’t get your hands on autoflowering seeds) but still want to produce big yields as fast as possible, the “Sea of Green” grow style may be a good option. Sea of Green is simply the idea of growing many small plants instead of just a few bigger plants. It works great for photoperiod strains to produce a quick harvest and great yields. It’s kind of halfway between “12/12 from seed” and a typical grow.
For this grow style, growers usually switch to 12/12 when plants are 4-6 weeks old. Since adding a little extra time to the vegetative stage often increases yields, you need to find a balance between getting to harvest as quickly as possible versus harvesting the biggest yields.
For SoG, wait to switch to 12/12 until plants are about this size or a little bigger (note: young plants like this can and will double or triple in height after the switch to 12/12)
SoG in Action – Make sure to fill the entire space under the grow light with plants and you will get a sea of buds!
12/12 from seed has a big problem. Learn about a better alternative called "Sea of Green" that gives you bigger yields in the same amount of time!