12-12 From Seed – Flowering Plants Early
The term “12-12” means you’re giving your cannabis plants 12 hours of darkness, and 12 hours of light every day. “12-12 from seed” mean you’re giving a cannabis plant a 12-12 light schedule from a very young age to force it to flower early (make buds).
Some growers are attracted to the idea of 12-12 from seed, because it means that harvest will come sooner. How long does it take to grow a plant from seed to harvest?
But does the 12-12 from seed technique work to give you a faster harvest, and if so, what are the results?
I have changed cannabis plants over to the flowering stage from seed, but no matter what the light schedule, plants don’t start flowering (making buds) until they are about 3 weeks old. Initiating a 12-12 light schedule at 3 weeks old from seed is as early as I’d recommend for this technique, if you choose to use it.
“12-12 From Seed” is a misnomer if you’re trying to force your cannabis to flower early – 3 weeks from seed is the earliest time a plant can start flowering after the switch to 12-12
Make sure to let your young marijuana plants get a minimum 2-3 weeks in the vegetative stage before changing them over to flowering. Your plants will be healthier and will start flowering at the same time as if you started 12-12 from when they first sprout.
Giving a 12-12 shedule when a cannabis plant is younger than that will not work to make the cannabis start flowering – a cannabis plant will only grow vegetatively for the first few weeks of life, and giving them less light will only cause them to grow more slowly.
Some strains of cannabis will naturally start flowering after about 3 weeks, and you don’t need to do anything with light schedules to cause that to happen. These strains are known as “autoflowering” or “Ruderalis” strains.
Many Growers Who Want To Force Cannabis Plants to Flower at a Young Age May Be Interested in Auto-Flowering Strains – No Need for 12-12 and Often Much Better Yields!
I have grown a few plants from seed to harvest just in a solo cup container. I was able to do this by flowering a plant from a young age – giving the plant 12-12 lighting when it was only 3 weeks old (pictured here).
These solo cup plants were able to survive their entire lives in a small container. I wouldn’t recommend a solo cup because they tip over easily, and plants are prone to nutrient and root problems once the flowering stage begins (the root space is just way too small, even when doing 12-12 from seed or using an auto-flowering stage).
But it’s possible.
The downsides… When your cannabis is kept in a too-small container, you will notice that you have to water your plant much more often than if you kept your plant in a big pot. As time goes on, plants are also more likely to suffer from nutrient problems and root problems because the roots aren’t being give enough room to spread out. When plants become root-bound this way, there’s not much you can do about this besides transplanting your plants into a bigger container.
While I wouldn’t recommend 12-12 from seed, and no longer ever use this technique myself, there are growers who are going to do it anyway.
For those growers who still want to use 12-12 from seed despite the warnings here…
If you are set on keeping potted cannabis plants in small containers for their whole lives, the smallest container you should try is a 1-gallon or 2-gallon container, like the pots pictured here.
Keeping plants in tiny containers may be important when growing in a very space-limited grow space, such as growing in a space bucket for stealth reasons.
There are powerful cannabis growth control techniques that will also allow you to grow high-producing plants, while keeping them short.
But like this extreme girl to the right (less than a foot tall and grown under CFLs), I’ve experimented starting the plants on 12/12 from seed to keep plants REALLY small.
When forcing your cannabis to flower early, plants will stay small and spend almost all their energy on producing flowers/buds on what few stems they have, instead of growing tall or making more colas/nodes.
Some people say that cannabis that is forced to flower too early will not make any buds, but that’s not true. The plant pictured here produced 0.75 ounces of bud after drying. So while 12-12 from seed may not be optimal, it does work.
The problems I’ve had with forcing cannabis to flower early is that since the plant is much smaller, you get smaller yields, but you’re still basically spending about the same amount of time to grow the plant as if you’d grown it bigger.
Compared to 12-12 from seed, growing an auto-flowering strain will generally give you bigger yields for the time, and will be less trouble
With such small plants, you don’t have the time to train your plant, which gives you much greater control over the final shape and size of your plant, improving yields without adding much time.
The other disadvantage to overly small plants is their inability to recover well from problems: you have fewer leaves as a ‘buffer’ so the plant can’t bounce back when something goes wrong such as a pest attack. In a too-small container, as roots get more root-bound, cannabis plants have a harder time using nutrients efficiently, and may start showing nutrient problems.
Growing extremely tiny marijuana plants is fun, but honestly you’ll get the biggest yields by instead investing a little more time in the vegetative stage to train your plant to grow into the exact shape you want. Or just grow an auto-flowering strain.
Auto-Flowering Strains – A better way to force plants to flower early
Plant Training Techniques – Make your plants grow how you want
Learn About Grow Lights – Which is best for your setup?
Learn what it means to give your plants "12-12 from seed" to force them to start making buds early.
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!