What is a photoperiod cannabis plant

Sunrise, sunset; the pattern of light and darkness affects us all. However, did you know it also guides the lives of some cannabis plants? Photoperiod plants have an internal clock that responds to the lengths of night and day helping them to time their flowering stage with the seasons.

In this article, we’ll shed some light (no pun intended) on what a photoperiod plant is, and how this built in mechanism influences their growth, flowering, and survival. We’ll also discuss various types of photoperiod cannabis plants and how this will affect your grow. 

What are photoperiod plants?

A photoperiod cannabis plant is a variety of cannabis that’s sensitive to light exposure. These plants rely on changes in the number of daylight hours to transition from the vegetative stage of growth to the flowering stage. 

Unlike autoflowering varieties that mature based on age, photoperiod cannabis plants need a specific number of hours in light and darkness to initiate the flowering process.

This is where the 12/12 and 18/6 light cycles come into play. During the vegetative stage you keep the lights on 18 hours of light and 6 hours of darkness to emulate the daylight hours of summertime. When you flip the lights to 12 hours of light and 12 hours of darkness you are telling the plant that winter is approaching. This triggers a survival mechanism in the plant which forces it to produce flowers before winter prevents it from doing so.

It’s this flexibility to control the plant’s life cycle that makes photoperiod strains the preferred choice for many growers.

Are all photoperiod plants feminized?

Not all photoperiod plants are feminized. Photoperiod plants can be either male, female, or hermaphrodite. The term “feminized” refers specifically to cannabis plants that have been bred to produce only female plants. 

This is achieved by subjecting a female plant to certain stress conditions, causing it to produce pollen. This pollen is then used to fertilize other females, which subsequently produce seeds that are virtually all female. 

However, this process is separate from photoperiod sensitivity. So while you can have feminized photoperiod cannabis plants, not all photoperiod plants are necessarily feminized.

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How long do photoperiod plants take to grow?

Photoperiod cannabis plants typically follow a longer growth cycle than their autoflowers. From seed to harvest, the timeframe can vary from 3 to 8 months, sometimes even longer. Their growth period is divided into two main phases: vegetative and flowering.

The vegetative phase, where the plant focuses on growing in size, can last anywhere from 2 to 3 months, depending on how big a grower wants the plant to become. Remember, bigger plants yield more. But, larger plants also demand more time and resources.

Transitioning to the flowering phase is triggered by changing the light cycle to simulate longer nights, typically a 12/12 light-to-dark ratio. The flowering stage then lasts 8 to 11 weeks on average, but can vary depending on the strain.

As you can see, the grower has control over the growth speed and size of photoperiod cannabis plants. If you are in a rush, you can shorted your vegetative stage down to 5 or 6 weeks simply by using the 18/6 light cycle for 5 to 6 weeks and then switching to a 12/12 light cycle to trigger the flowering stage.

Can you make a photoperiod plant grow faster?

While the growth cycle of photoperiod cannabis plants is guided by light exposure, there are ways that you can speed up their growth. You can also play with light cycles to make initiate flowering earlier. Although this won’t necessarily make them grow any faster, it will reduce the total growth time. Lets take a look at the ways that you can both speed up growth, and reduce growth time.

How to make a photoperiod grow faster

Keep your plants healthy and avoid stress

Maintaining optimal environmental conditions such as temperature, humidity, and lighting will support faster and healthier growth. Keeping the temperature between 70-85 degrees Fahrenheit and the humidity around 40-70% during the vegetative phase and 40-50% during flowering can be beneficial. Stress can stunt the growth of a cannabis plant and slow down the rate of maturity so keeping your plants happy and avoiding any stress will keep your schedule on track.

Get the nutrients right

Cannabis plants require a mix of macronutrients and micronutrients, with different ratios needed during the vegetative and flowering phases. By getting the nutrients right your plants will grow faster and bigger. The bigger your plant grows in the vegetative stage, the earlier you will be able to switch to the flowering stage.

Using plant training to speed up growth

Lastly, by using low and high stress training techniques to manipulate the growth pattern of your plant you can force it to produce a wider, flatter canopy structure. This allows the plant to absorb more light optimizing its energy consumption. The result is faster growth and bigger yields.

How to reduce the growth time of photoperiods

Once in the flowering stage there is a set number of weeks that a photoperiod plant needs for its flowers to mature, this is usually between 8 – 12 weeks. You can’t really speed up the flowering stage because if you harvest before your flowers have fully matured your bud will lack potency and flavor. You can identify the peak period of maturity by assessing the color of a plants trichomes.

The vegetative stage on the other hand can be sped up. There is no set length of time that a photoperiod should stay in the vegetative stage. Therefore if you want to cut down your grow time, you can simply manipulate the vegetative stage.

Let’s say you have a window of 12 weeks to grow your plant and you know it needs 8 weeks in the flowering stage. You can keep your light cycle on 18/6 for 4 weeks of vegetative growth and then flip the lights to 12/12 for the final 8 weeks of flowering growth. Your plants won’t be huge but if your goal is to grow from seed to harvest in 12 weeks this is how you can achieve it.

How long should you veg a photoperiod?

The length of the vegetative phase for a photoperiod cannabis plant is not fixed and largely depends on the grower’s preference.

Generally, indoor growers keep their photoperiod plants in the vegetative stage for 4 to 8 weeks, allowing the plants to develop a strong root system and a good amount of size. This period can be extended if you want larger plants, but keep in mind that cannabis plants typically double or even triple in size during the flowering phase, so you’ll need to ensure you have enough space.

Outdoor growers, on the other hand, are bound by the natural seasons. The plants usually start vegetating in spring and early summer and then begin flowering as the days start to get shorter, which is typically in late summer to early fall.

Remember, the goal during the vegetative phase is to create a strong and healthy plant that can support heavy, dense buds during the flowering stage. Rushing this phase might result in a weaker plant with smaller yields.

What are the pros and cons of growing photoperiods?

Growing photoperiod cannabis plants brings its share of advantages and challenges.


  1. Control Over Growth: Photoperiod plants allow you to control the length of the vegetative stage, meaning you can manipulate the plant’s size and yield based on the growth period and techniques employed.
  2. High Yields: Given the right conditions and care, photoperiod plants typically yield more than their auto-flowering counterparts because they have more time to grow and develop.
  3. Resilient: They’re generally more resilient to stress, making them ideal for training techniques like topping, pruning, and LST (Low Stress Training) that can enhance the yield.


  1. Longer Growth Cycle: Photoperiod plants take longer to grow, requiring more time and attention from the grower.
  2. Light Dependency: Their flowering is triggered by changes in light, meaning they require a specific light cycle to transition into the flowering stage. Any interruptions or mistakes in this cycle could potentially stress the plant.
  3. Male or Female: Unlike feminized seeds, photoperiod seeds can be either male or female. Unless you’re planning to breed, male plants are undesirable as they don’t produce buds and can pollinate females, leading to seedy buds.
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What are the stages of growth for a photoperiod?

Photoperiod cannabis plants go through distinct stages of growth, each with its unique characteristics and care requirements.

  1. Germination (1-2 weeks) : This is when your cannabis seeds sprout. Providing a warm, humid environment encourages the seeds to germinate.
  2. Seedling Stage (2-3 weeks): After sprouting, your plants enter the seedling phase, the most vulnerable stage. It’s crucial to maintain optimal light, temperature, and moisture during this time.
  3. Vegetative Stage (4-8 weeks): Here, the plant focuses on growing larger and developing a strong root system. The light cycle is usually set to 18 hours of light and 6 hours of darkness, and the plants require higher levels of nitrogen to support leaf and stem growth.
  4. Flowering Stage (8-11 weeks): Triggered by adjusting the light to a 12/12 cycle, the plants shift energy towards bud production. The nutrients are also shifted towards higher levels of phosphorus and potassium. It’s during this stage that female plants will produce the cannabis buds we all recognize.
  5. Harvest: Timing your harvest right is critical to the potency and flavor of your buds. Look for signs like the color of the pistils and the trichomes to determine the optimal harvest time.

By understanding these stages, you can effectively cater to your plant’s needs at each phase, ultimately leading to a successful and fruitful harvest.

Tips on how to grow a photoperiod strain

Growing a photoperiod cannabis strain can be a rewarding endeavor with the right approach. Here are some essential tips:

  1. Understand Light Cycles: Ensure you’re familiar with the light requirements of photoperiod plants. Typically, a 18/6 light-to-dark cycle is maintained during the vegetative stage, and switched to a 12/12 cycle to induce flowering.
  2. Optimize Environment: Aim for ideal temperature and humidity levels. A range of 70-85°F during the vegetative stage and slightly cooler during flowering works well. Humidity should be higher in the early stages and reduced during flowering to prevent mold.
  3. Nutrient Management: In the vegetative stage, focus on nitrogen-rich nutrients. In the flowering stage, switch to nutrients higher in phosphorus and potassium.
  4. Training Techniques: Apply plant training techniques like topping, low-stress training, or the Screen of Green method to control plant growth and increase yield.
  5. Monitor Plant Health: Regularly check for signs of pests, disease, heat stress or nutrient deficiencies. Prevention is easier than cure in growing cannabis.
  6. Patience is a Virtue: Photoperiod strains require a longer growing period than autoflowers. Patience is key to allow your plants to mature fully and yield a substantial harvest.

Remember, each strain may have unique requirements, so be sure to do your research and be responsive to your plant’s needs throughout the growth cycle.

Photoperiod cannabis FAQ

Are photoperiods more potent?

Potency in cannabis plants depends on multiple factors, including genetics, growing conditions, and harvest time. Photoperiod strains have the potential to be more potent than autoflowers, given their longer growth cycle allows for more time to develop and mature their cannabinoid content. 

However, the quality of cultivation plays a significant role, and a well-grown autoflower can certainly match a poorly grown photoperiod in terms of potency.

When should you top a photoperiod plant?

Topping a photoperiod plant is generally done during the vegetative stage, once the plant has developed 4-6 nodes. This is typically a few weeks into the vegetative phase. By topping the plant at this point, you’re allowing it time to recover and grow more branches before switching to the flowering phase. Remember to provide your plant with ample nutrients and water after topping, as the process can be stressful.

Do photoperiod plants yield more than autoflowers?

Yes, photoperiod plants typically yield more than autoflowers. This is primarily due to their extended vegetative stage, which allows for more time to grow and develop. They can also be manipulated through various training techniques to maximize yield. 

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Iris Sideris

Meet Iris, the ultimate cannabis connoisseur! With her green thumbs and a puff puff pass mentality, Iris loves sharing her stash of knowledge on all things cannabis. Whether you're a seasoned smoker or a newbie to the ganja game, Iris is the go-to source for all things 420.

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