How much do Cannabis Plants stretch during 12/12 Light Cycle? (2024)

What you need to know:

When you switch to 12/12 light cycle, your plants will stretch
Stretching continues through the first 2-3 weeks of flower cycle
Your plants will double or triple in height
Your must get this under control or there will be harsh consequences
Use trellis netting to control the height
Defoliate early in flower to control the bush

Read on for in-depth instructions….

Welcome to the art and science of Cultivating Cannabis indoors

If you are new to growing cannabis, then welcome to the club! Those of us that grow weed are a small, but growing, community around the world that love the herb. Some of us grow commercially, some us of are caregivers, some of us are average Joes and Janes who grow at home. What we all have in common is a love for the herb.

Growing cannabis used to be extremely underground due to the criminal penalties and harsh consequences of getting caught. Therefore, knowledge and information was shared only in really small circles. With the increasing acceptance and legalization of cannabis, in the United States and around the world, more and more people are getting into cannabis, and more and more professionals are opening up and sharing information.

Which is exactly what we want to do here at Smokey Okies Cannabis. We want to share what we have learned so you can save yourself from making the same mistakes that we did when we first got started in the cultivation game.

In this article, we will address the question of how quickly and how much your plants will stretch when you change the light cycle to a 12/12 flowering cycle.

The difference between Vegetative and Flowering Light Cycles

As we explain in our series How to Grow Indoors, cannabis is a photo period plant, with two distinct phases of growth: the vegetative phase, and the flowering phase.

During the vegetative phase, the grower provides much more light than darkness, such as 18 hours of light, and six hours of darkness. There are many variations, such as 20/4, or keeping the lights on 24 hours a day.

With all of this light, the plants grow, but remain immature. This excessive amount of light will not allow the plants to bud, to develop the “fruit,” i.e. the nugs that we cherish.

This extra recovery time from 12/12 light cycle causes the Post-Veg Stretch, where plants will double or triple in Height.

This is what you need to know: after you have “flipped” you plants from veg to flower (by switching the light cycle to 12/12), you plants will shoot up in height. Do not be surprised to see impressive growth after 4 or 5 days.

Not only will they have growth spurt that makes them taller, they will also bush out, with the number of fan leaves multiplying like crazy. By the second week, the plant can become wild and crazy if not tamed.

In the first 2-3 weeks, you plants will double, and eventually triple, in height, though this ultimately depends on the cultivar itself. Some strains are known for stretching into pure vines, while others will bush out and just get hairy. Many do a combination of both.

Both Sativa and Indica plants stretch during the first three weeks of 12/12 light cycle

Here is another hint: beware of the myth of sativa vs. indica growth characteristics. If you’re not familiar, the old tale goes like this: sativa plants grow tall, with long intervals between node spacing, and skinny fan leaves, while indica plants grow in a short, bushy pattern.

While both of these growth patterns absolutely exist, they are not limited to these distinct categories of sativa and indica. You will find that a strain that is supposed to be indica dominant may grow extremely tall and vice versa. So know that these patterns exist, but beware that thinking that your plant will automatically be one or the other based on the categorization of its lineage as a sativa or indica.

Regardless of the lineage, it is guaranteed that your plant will stretch during the initial switch to flower, even though the amount of stretching may vary strain to strain.

Now that you are aware that your plant will at least double in height during the first two weeks, what else do you need to know to ensure a good outcome?

You must control the stretch and the over-growth to increase yield potential and avoid problems later in flower

There are several reasons why it is important that you take control of the situation immediately. One, you do not want your plants growing into your lights. Two, you do not want overgrowth to prevent light penetration through the canopy. And finally, you want to control the thickness of the bush to prevent other problems with mold and mildew potential.

There are ways you can control and tame this plant all while it continues to grow and stretch like crazy.

The best tool to use for this is trellis netting, although you can use bamboo sticks or other stakes and attempt to tie the plant down.

But with trellis netting, you can weave the vine through the netting and achieve the most desired method of indoor flowering, which is to create a Screen Of Green (SCROG). Why, you may ask?

When flowering cannabis indoors, you want to create a horizontal canopy to increase your yield.

Your plants are stretching, and that is a healthy sign, but you must control the situation or it will control you. Unless you want minimal yield, you cannot let them grow tall and skinny. You must train them to grow wide, horizontally, and there are several ways to do this.

Prepare your plants during the vegetative phase

First, it all starts in veg. During veg, you should top your plants. Topping causes the plant to fork. Topping can be done multiple times in veg which will divide long branches and start the process of training your plant to grow horizontally instead of just straight up.

Continue your training during the flowering stage

Next, you take that topped plant into flower, and as those vines stretch, you tuck them back under the trellis. Imagine a tall, skinny branch, that is sticking straight up vertically. Imagine laying that branch down, by grabbing the very top, and pulling down sideways and tucking it several squares away from the square it is originating from.

The top of that branch is now pointing sideways… at this very moment. Come back in a few days and it will be pointing up, wanting to stretch vertically from the square it is in. What’s more, further down the branch, nodes that would never have gotten any attention are now on top of the squares, and are pointing up as well.

Each of these nodes now has the potential to be a separate cola. By simply laying over a single branch, you created three or four new colas. Imagine if you do this with multiple branches. Do you see the value in Topping your plants during veg?

By weaving the vines through the trellis, you are able to create a wide canopy, which will greatly increase your yield, as opposed to growing a tall, skinny plant.

Take control of the stretching to increase your yield at Harvest Time

When you increase the square feet of your canopy, you maximize your yield with the existing light. This is very important as you are not increasing energy expenditure. You are making use of light that is already there! This can and should be done whether you are growing on tables in a room, or inside a grow tent.

In addition to using trellis to create a wide canopy, you must also defoliate your plant. This will help you achieve a better outcome for several reasons.

Defoliate early in flower to maximize light penetration and remove plant material that has zero potential to become dense bud.

Along with the stretching that occurs early in flower, you plants will bush out and be consumed in fan leaves and plant material.

Do not be fooled into thinking that every node and top that appears will yield smokable flower for your enjoyment. Quite to the contrary, most of those little nodes below the top half of the plant will struggle to fully develop. Those that do will amount to fluffy larf, will weigh nothing on a scale, and will lack the qualities of fully developed and mature buds that make up the larger colas near the top.

What’s more, is that this messy bush, which is preventing light penetration anyway, has the potential to restrict airflow, and can contribute to conditions that support mold and mildew.

It is best to simply remove it all by defoliating your plant.

We have found a best practice in performing a heavy defoliation of the entire plant in Week 2 and Week 4 of Flower. Additionally, we also remove all of the small branches that are in the bottom half. These will never amount to anything, and they merely suck energy from the upper half of the plant.

By removing all of the inner fan leaves, you open up the canopy for new growth, new branches that can then poke through the canopy and become colas. You also allow light to penetrate and grow the nodes that are just below the surface of the canopy.

You shave everything off down below, and you have now set yourself up for success in maximizing the yield of your plant during the second half of flower.

If you’re interested in learning more about growing indoors, be sure to check out our blog. Don’t forget to subscribe to our newsletter.