Is 12-12 From Seed Worth It?

Updated Jun 07, 2020

by Nebula Haze

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.

This weed plant in a solo cup is already way to big and should be transplanted to a bigger pot ASAP

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!

This cannabis plant was given a light schedule of 12/12 from seed - although it looked pretty cool, it didn't end up yielding very much

 

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.

Sea of Green (SoG) setup

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)

Sea of Green example in the flowering stage

A few weeks of extra light, in the beginning, seems to achieve plants with longer and fatter buds (why was this plant defoliated?)

Cannabis plant growing with one main cola after being switched to 12/12 at around 3.5 weeks old from seed

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.

Example of a cannabis plant growing in coco coir - look at those huge buds!

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!

This micro marijuana plant was started as a clone and was forced to start flowering immediately.

 

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.

This auto-flowering cannabis plant has been flushed and is ready to harvest!

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.

This auto-flowering plant was 3 months old (from seed) and yielded about 2 ounces of bud

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)

Switch to 12/12 when plants are around this side in order to start a SoG (sea of green) style cannabis grow

SoG in Action – Make sure to fill the entire space under the grow light with plants and you will get a sea of buds!

Amazing example of well-trained cannabis plants - training your plants this way can increase your yields by up to 40%

Check out the Sea of Green tutorial

 


 

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