When To Switch To 12/12 Light Cycle?

(Last Updated On: November 14, 2021)

The first time you cultivate an indoor garden, light cycles are always an issue. It’s simple after you’ve mastered the fundamentals. One of the most significant components in ensuring the success of your plants is knowing when to switch from the vegetative to flowering stage.

Usually, growers switch to a 12/12 light cycle to transform their plants from the vegetative to the flowering phase. This switching initiates the growth of buds and forces flowering. So when a grower wants to eliminate the long-lasting vegetative stage and move faster to the flowering stage, he can use this 12/12 light cycle.

Switching too soon can result in a lower overall yield. Making the changeover too late, on the other hand, can result in overgrowth or scorched buds. So the decision of when to switch to 12/12 light cycle must be taken under a lot of consideration.

The 12 /12 Light Cycle

If you are a beginner, firstly, you should know what a 12/12 light cycle is. Most indoor growers use different types of light cycles as they lack natural light. The numbers here define how many hours one should keep the lights on and off. 12/12 light cycle means keeping the lights 12 hours on and 12 hours off.

The 12/12 light cycle strains the plants while also providing a few benefits to the gardener.

One is that it can transform the plants’ sex to female by forcing flowering. The growing period is extended by 7-9 weeks using the 12/12 lighting strategy. Additionally, the vegetative stage of growth is eliminated with this strategy. It may assist some growers in saving space and time.

Plants will begin to generate flowers as soon as they start to grow if you use a 12/12 lighting approach from the start. The illumination pattern mimics the conclusion of the growing season, fooling the plants into believing they must begin flowering right away.

When Should I Flip To 12/12?

Growing indoor plants is a lot of fun. An indoor grower’s delight is watching growth cycles progress from seed to full-blown bloom.

The transition from vegetative development to pre-flower bud creation, when delicate white pistils begin to emerge on the plant, is one of the most pleasurable stages for many.

A plant’s photoperiod, or the amount of light received each day, determines how quickly the plant grows. As the days grow shorter following the Summer Solstice, plants cultivated outside in natural light enter the flowering phase.

Indoor plants that receive plenty of light on an 18/6 or 24/0 cycle during veg time must be switched to a 12-12 cycle to trigger flowering.

Redirecting energy flow from increasing vegetative development to bud formation during reproduction occurs when daylight hours are reduced. This redirected energy provides nutrients to grow huge, thick trichome-rich blooms since a plant can store more carbohydrates during additional dark hours.

When To Switch To Flowering Light Cycle?

The 12/12 light cycle is known to be the flowering light cycle as it forces flowering. But it is very crucial to know the perfect timing to switch to the flowering cycle because wrong timing will affect your production.

Here are a few things that you should consider before you decide to make the switch.

Maximum Height Of The Plant

The amount of room available for your plants is the most crucial consideration. Plants will grow higher if they are left in a vegetative state for a long time. As a result, vegging your plants in a tight place for too long can cause them to overgrow.

Plants that grow too tall can possibly reach too close to lighting systems, causing damage. Plants should never be allowed to go closer than 30cm to the lights above them. This is merely a guess.

On the other hand, growers also run the risk of burning or frying their blooms if they let them go any nearer.


When transitioning to the flowering stage, the genetic variations between Indica and Sativa strains should be considered. That’s because Indicas and Sativas function differently during blooming.

As opposed to their Sativa cousins, Indica strains produce shorter, thicker, and bushier plants. During the flowering stage, they will typically acquire only 25–50 percent of their original height.

Sativas, on the other hand, are recognized for their height and capacity to continue growing taller during the flowering cycle. From the first day of blossoming until harvest, they have been noted to double in size.

Growing Methods

The switch can be affected by a variety of growth strategies, including the sea of green (SOG) method, the screen of green (ScrOG) method, super cropping, and lollipopping. Your flowering time will most likely vary depending on which strategy you use.

1.    Sea Of Green (SOG)

This strategy is based on plants blossoming early enough that just one huge bud is produced. SOG is most commonly used with Indica strains that are densely packed in the grow space.

Plants should be flowered after they reach a length of 15–30cm when employing this approach.

2.    Screen Of Green (ScrOG)

A mesh screen is placed horizontally over the plants in this manner. The screen is usually positioned 30–60cm above the plant’s base. As a result, it permits them to mature faster.

The ScrOG method requires plants to stay in a vegetative condition for several weeks longer than the SOG technique.

3.    Super Cropping

This strategy is intended to deliver massive harvests from a small number of plants. As a result, plants cultivated this way must spend more time in the vegetative phase.

Super cropping is the practice of bending top branches down to ensure more light to pass the plant’s lower portions. This maintains the plant’s height under control during the growing process, allowing for a more prolonged vegetative stage.

4.    Lollipopping

Plants’ lowest growth, which absorbs almost no light, is removed using the lollipop approach. Because plants require sunlight to thrive, these areas will generate smaller buds and deplete the plant’s energy, which could be spent otherwise.

The lower branches and bud sites can be removed so the plant can focus its energy on the top colas, which produce denser, thicker nugs. A height-based flowering switch is usually used in this manner.

Because they develop so much throughout the flowering cycle, Sativas are frequently switched when they reach 30–45cm. When Indicas reach a height of roughly 100cm, they are switched, allowing them to spend longer time in the vegetative condition.

Seeds Or Clones

The time of the transition will be affected by the planting method used for the growth. The plant’s root system will grow at a different rate depending on whether it is produced from seeds or clones. There may be challenges and complications during the flowering period if the plant has not formed a robust root system.

Clones can quickly become very tall, forcing farmers to switch to flowering solely based on plant height. Growers should, however, ensure that their clones have enough time to establish fully before flowering. Seedlings can flower considerably earlier, but keep in mind that it will take 2–3 weeks for them to do so.

Light Cycle For Weed

During the first two stages of plant growth, it’s critical to keep a close eye on your light cycles. You must maintain track of two stages: the vegetative stage and the flowering stage.

Vegetative Stage

Maintain a minimum of 18 hours of growing light for plants in the vegetative stage. However, if you’re one of those growers that want their plant to grow as big as possible, you can maintain it under 24-hour indoor lighting.

Indoor plants do not begin to flower until they have been exposed to 12 hours of continuous darkness. They will remain in the vegetative stage if this does not happen. You may keep your plants in this arrangement as long as they get about 13 hours of light every day.

Flowering Stage

The majority of growers who grow their plants indoors start at 12 hours of darkness after they have acquired the proper size and shape during their vegetative phase. Most growers prefer a 4-8 week indoor vegetative stage under a 24/0 or 18/6 light cycle.

You must mimic the natural development pattern of the plant to cultivate it properly indoors. When you grow plants outside, the days get shorter, and the plants need at least 12 hours of complete darkness to form buds.

Simply reduce your light consumption during the plant’s life cycle from 18 to 24 hours of excellent sunlight each day to 12 hours of light and 12 hours of darkness.

Best Light Cycle For Flowering Stage

Both indoor and outdoor growers follow a particular schedule of light cycles in the flowering stage. Here’s a basic rundown of how it differs based on whether you grow the plants indoors or outdoors.

For Outdoor Plants

When flowering photoperiodic plants outside, you must exercise extreme caution and forethought. As you may be aware, each season has its own cycle, which will decide how long your plant develops before flowering. To manage the light, you can use light deprivation techniques. This entails covering your plants with a dark sheet to keep light out.

Autoflowering plants do not require a vegetative stage and will grow and flower at the appropriate age. This makes them far more manageable to grow than photoperiodic plants.

An excellent suggestion is to see how much daylight you’ll have each month on the internet and plan your harvest appropriately. Your plants will then benefit from the extra hours of sunshine.

Even though auto-flowering plants can blossom all year, it can boost the quality and yield of your harvest by a little amount, and you can harvest outdoor plants early.

For Indoor Plants

On a 12/12 cycle, photoperiodic flowers blossom to their fullest potential. When growing indoors, follow the exact care instructions as you would outside. However, flowering indoors can be more convenient due to the lack of preparation required. Simply change your timer’s cycle from 18/6 to 12/12 once your plants reach their full potential.

Your plants may take a few weeks to enter the pre-flowering stage and exhibit signs of maturity, but you’ll soon see lovely buds emerging.

There isn’t much to do with auto-flowering plants. Vegetative light cycles cause them to flower as soon as the seed is sown. You will not have to change anything except the nutrient mix if you start them with an 18/6 cycle from the beginning. They will go through the complete cycle: seedling, vegetative and blooming stages.

If you’re an autoflower grower looking to try something new, you can experiment with alternative cycles like 18/6, 20/4, or 24/0.

Best Light Cycle For Veg

Plants in the vegetative phase need a lot of light because it’s what they utilize to photosynthesize and grow strong and healthy. Therefore the more light they get, the more and better they grow.

The most typical vegetative stage light cycle is 18/6. However, it can be any mix of light and darkness such as 20/4, 19/5, or 17/7 as long as they don’t get more than 12 hours of darkness each day, which will cause flowering.

Keep in mind that giving your plants less light can cause them to develop more slowly. So if you’re not sure, stick to the 18/6 light schedule and only offer them additional light (such as 20/4) if you’re sure your plant can handle it.

However, the most common light schedules for vegetating plants are 18 hours of light and 6 hours of darkness, or 20 hours of light and 4 hours of darkness.

Giving them more light does not always result in faster or more development. Doing so can hurt or stress your plant, causing them to become hermaphrodites or show other heat stress signs.

12/12 Light Cycle For Seed

When the plant is first planted, it gets 12 hours of light, followed by 12 hours of darkness, which gives the process its name. The strain will begin to flower after it has reached sexual maturity.

The outcomes of this method of growing will be plants with a smaller height than those grown in the usual way. This might be particularly appealing to individuals who have a very restricted growing space.

You can grow Sativa indoors with this strategy since you can control their growth a little. Some gardeners advise against using this method on Indica cultivars because they can get too tiny.

Furthermore, by giving the plants less light for fewer hours, you will save money on electricity and, in general, the harvest will be faster.

When To Change From 18/6 To 12/12?

The 18/6 schedule is the most popular among autoflower farmers because it offers adequate light for healthy plant growth, allows them to rest, and is relatively inexpensive. But indoor plants that receive plenty of light on an 18-6 or 24-0 cycle during the vegetative phase must be switched to a 12-12 cycle to start flowering.

When daylight hours are reduced, energy flow is shifted from growing plant development to bud forming during reproduction. Because a plant can store more carbs during hours of normal dark period, redirected energy now offers nutrients to build large, thick trichome-rich flowers.

So to trigger the early flowering stage to increase the production, you should change the light cycle from 18/6 to 12/12.

How Long After Switching To 12/12 Will I See Buds?

It could take anywhere from 7 to 12 weeks to flower, depending on the strain and genotype. So, if it’s more Indica, it’ll blossom faster. As for how quickly flowers form, it might take anything from two weeks to a month, depending on the strain and phenotype. However, they will go into flowering mode.

Another practical approach to speed up the flowering process is to place the plant in darkness for 24 hours. Depending on whatever nutrient line you choose, you will get more remarkable results with bloom boosters, base nutrient blends, sweeteners, and bud hardeners.

Frequently Asked Questions (FAQs)

When to switch to the 18/6 light cycle?

You should switch to an 18/6 light cycle if the plant is in the vegetative phase. It encourages the plant to increase production.

How do you switch to a 12-12 light cycle?

For best results, turn off the lights 12 hours before dark and turn them back on 12 hours before dawn. For the first two days, make sure the timers are set correctly by checking the grow room at the start and conclusion of each 12-hour cycle.

Can your plant have light 24 hours?

Yes, it can, particularly in the vegetative phase. That’s because the presence of more lights resulted in higher vegetative growth. However, as it re-vegetates throughout the blossoming stage, this could be a concern.

When should you induce flowering?

Once the clone has formed a robust root system, growers can move on to the flowering stage. In ideal circumstances, plants should be kept in the vegetative stage for 60 days. This time frame should allow the plant to maximize productivity while also acclimating to growing circumstances.

Final Words

To stay in the vegetative phase, plants require at least 13 hours of light per day, and just a few ‘long’ nights may be enough to initiate blossoming. Plants begin to blossom when they have at least 12 hours of “uninterrupted” darkness each night. This will have to continue till the harvest is complete. Flowering will be hampered even if darkness is interrupted for a short time.

Changing the light cycle following the vegetative stage to the flowering stage is a must for all plants. It determines the amount of cultivation. But to do so, you should have explicit knowledge about the timing. Otherwise, the result can be damaging.

So after a lot of research and discussion, we have come up with this detailed article on when to switch to 12/12 light cycle to answer all your questions regarding this. Apply the suggestions we have given, and hopefully, you will enjoy a good harvest!

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