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Weed Plant Stages and the Best Light Cycle for Weed

weed plant stages

What’s the most significant factor that plays a make-or-break role in the growth and final yield of cannabis crops? You guessed it right; it’s none other than light.

Read the following guide to learn about the weed plant stages if you want to master the science of growing premium-quality cannabis and better yield.

As a grower, you must understand the cannabis growth processes, corresponding photoperiods, and environmental and nutritional needs. Whether you grow cannabis plants indoors or outdoors, the proper use of lighting allows for maximizing crop yield and quality.


Cannabis Light Cycles Basics

Don’t take cannabis similar to other plants; instead, it’s a photoperiod plant. Hence, the received amount of light determines when the cannabis plants start flowering during the life cycle.

So, what does the light cycle for weed essentially mean? In simple terms, it’s the fraction of the total time when the light is on over the entire duration when the light is off.

For example, 18/6 means the marijuana plants are exposed to light for 18 hours while there isn’t light exposure for six hours. Similarly, 12/12 means the light is on for 12 hours while the plants spend the next 12 hours in darkness.

At this point, you must be wondering why it is essential to understand different light schedules and female weed plant stages. It’s because all plants require exposure to light to photosynthesize. The plants use sunlight to synthesize the nutrients from carbon dioxide and water.

However, in the case of photoperiod plants such as cannabis, the growers should limit the light exposure to 12 hours during the flowering stages.

As a result, it leads to a lot of confusion among the growers, especially the beginners, regarding selecting a suitable light cycle for different cannabis growth stages. Therefore, keep reading to learn about the plants’ processes and the respective light cycle to enhance the final yield.


Understanding Cannabis Plants Processes

Until now, we have established a basic understanding of the role artificial or natural light plays in boosting cannabis plants’ growth. Furthermore, marijuana plants undergo different stages as they grow, requiring different nutrients, water, and, most importantly, the amount of light.

Once you comprehend the cannabis growth stages and their total duration, you’ll ensure the desired growth and development for better yield. For example, a cannabis seed usually takes ten to 32 weeks, translating to three to eight months to become a complete plant.

Similarly, it’s also essential to understand when to grow marijuana. For example, outdoor growers receive the seeds between February and April in the Northern Hemisphere. Next, they sow the seeds by the end of April.

Since the seedlings are delicate, some growers sow them in a controlled environment indoors before transferring them to an outdoor environment. Alternatively, you can have a grace period of a month if you don’t buy seeds and grow clones or autoflowers.

You should remember that your cannabis plants should be outdoors by the end of June. Lastly, the harvest usually happens between September and November, depending on the local weather climate.

On the other hand, there isn’t any time restriction while growing indoors. However, you need to invest in proper heaters, fans, and ACs to facilitate the cannabis growth stages.


Photosynthesis and Cannabis Plants

Let’s discuss how light affects the photosynthesis process in marijuana plants. As the name suggests, photosynthesis comprises the following two primary steps:

  • Light-dependent cycle
  • The light-independent cycle, also known as the Calvin cycle


For example, plants use light and water during the light-dependent cycle to form energy in the form of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH).

What happens is that this created energy further steers the synthesis of carbohydrates in the following Calvin cycle. It’s light-independent as it isn’t directly linked to light exposure; instead, it uses the energy generated in the first light-dependent cycle. Finally, in the second stage, the plants use the carbon dioxide from the air to create carbohydrates.


light cycle for weed


Seed Germination 16/8 (3-10 Days)

During the germination phase, it’s vital to fulfill the following conditions for the cannabis seeds:

  • Warm temperature
  • Humidity
  • Air
  • Water


Hence, place the cannabis seeds in a damped napkin in a closed jar. Next, you can place the jar in a dark and warm place.

The cannabis plant focuses all its energy on developing a root system during the germination cycle. Once you see the first white taproot, you can place the seeds in the growing medium, such as soil or coco, in a pot.

Here, you need an optimal cannabis light cycle of 18/6, translating to 18 hours of light and six hours of darkness.

Some growers experiment with the marijuana light cycle by changing it to 20/4 or even 24/0. However, it certainly increases your electricity bill by running the lights, AC, and fans on all day long. Nonetheless, 18/6 is the optimal light cycle for weed if you don’t want to experiment or incur higher electricity costs.

Here, the initial root development happens when you’ll finally able to see the first two rounded cotyledon leaves. Congratulations, you can now proceed toward the seedling phase.


Cannabis Seedling Stage 16/08 (2-3 Weeks)

It’s important to understand that the seedlings don’t require intense or bright light to grow—all you need to ensure a safe distance between the bulb and marijuana plants. If you place the bulb away for the plant, it will stretch; however, placing the light closer can burn the plant.

As a general rule, you can use a LED and place it at a distance of 24 to 30 inches from the seedling.

Additionally, you need to be extra careful about the proper growth of the Cannabis seedlings by ensuring the following factors:

  • The temperature should be warm, ranging from 22C to 27C degrees.
  • 65 to 80 percent relative humidity.
  • It’s better to opt for low light intensity or preferably blue spectrum light.
  • A photoperiod of 16 hours of light exposure and eight hours of darkness.
  • A pH level between six and seven.


After germination, you can place the seedling in a small pot to facilitate excess water drainage. One of the most significant advantages of keeping the seedlings in a small pot is to ensure root development and strengthening. You can plant the seedlings in the final container after a few days.

Additionally, you need to start with a relatively low dosage of nutrients and gradually increase the amount. Lastly, you shouldn’t overwater or drown the baby marijuana plants; instead, limit the watering and implement a proper drainage mechanism.

After the appearance of the cotyledons, the cannabis seeds produce serrated leaves. Furthermore, new leaflets and leaves grow from the seedlings until you see digitated leaves with serrated borders. These leaves are essentially cannabis fan leaves.

The appearance of the fan leaves marks the beginning of the vegetation stage. The seedling stage usually takes up to three weeks to complete.


Vegetative Stage 18/6 (3- 16 Weeks)

The primary purpose of the vegetative stage is the root system development and strengthening of the main stem of the cannabis plant. Moreover, the stems and the leaves begin to grow taller and larger in this phase.

However, the weed plants don’t produce any buds in this phase; hence, you’ll have complete control over the size and shape of the plants. The plant grows out of the foliage to gather more light and convert it into useful energy.

In addition to photosynthesis, you should also understand another process, known as phototropism. This process informs the marijuana plants about the direction of the incoming light. As a result, the plants grow in such a way as to orient themselves toward the light.

Hence, the plants stretch and grow taller in search of a light source. Therefore, you can manipulate light in the veg stage to enhance the plant’s growth and yield. That’s why cannabis plants require 18 hours of exposure to light, with six hours in darkness, also known as the 18/6 cannabis light schedule.

In the vegetative stage, marijuana plants grow in size and height under the right conditions. You should know that marijuana plants don’t develop flowers unless they receive 12 hours of darkness; else, they’ll remain in the vegetative stage.

Depending on the strain type, some small cannabis plants can begin the flowering period from the fourth week of the vegetative stage.

Your primary goal should be to give more vegetative time allowing the female plants to get bigger and taller before switching the light time to 12/12 in the flowering phase.


Indoor Vegetative Cycle

In this stage of growing cannabis indoors, you should use full-spectrum lights, such as LED grow lights, to ensure a healthy life cycle.

On the contrary, you shouldn’t use high-pressure sodium (HPS) lamps as they contain only three to four percent blue light. However, the desired amount of blue light is 12 percent at least to facilitate the proper marijuana plant’s growth.

Growing cannabis plants indoors, you can use automated timers, especially during the vegetative stage. As a result, you can manage the cannabis light schedule accurately and consistently.


Outdoor Vegetative Cycle

Usually, the growers keep the marijuana plants indoors before moving them outside for direct sunlight. For example, the growers keep the seeds or the clones under 16 to 18 hours of continuous light indoors during March or April. Later, they move the cannabis plants outdoors at the beginning of May or June.

This way, you can keep the delicate marijuana plants indoors to prevent the danger of frost, sudden temperature drops, or late spring snowfall.


Summary of Vegetative Stage

You must ensure the following conditions are met in the vegetative growth:

  • A warm temperature between 22C to 26C degrees.
  • The humidity levels should remain between 40 and 60 percent.
  • You can opt for increased light intensity, such as blue spectrum.
  • Proper airflow and ventilation allow the plants to extract carbon dioxide.
  • The pH levels should remain between six and seven.
  • 18 hours of light exposure and six hours of darkness period.
  • Set a feeding schedule and stay consistent with it.
  • Don’t overwater the plants and ensure proper drainage.


Many growers opt for 16/8, which leads to slower vegetative growth as the light intake is lesser. Alternatively, some growers use a lighting schedule of 20/4, resulting in their light exposure and a higher electricity bill.

You can also experiment to find the right amount of light for a particular female cannabis plant you are growing. Nonetheless, 18/6 is the optimal cannabis light schedule for vegetative growth.


Flowering Stage 12/12 (8-11weeks)

(Initiation, Mid-Flowering, Late-Flowering/Ripening)

It’s the final stage of the marijuana plant life cycle, where you need to switch to a photoperiod of 12 hours of light and 12 hours of uninterrupted darkness to begin the flowering period. This stage lasts for eight to 12 weeks with a regular 12/12 light schedule.

However, if the light is less than 12 hours, the bud production will be severely affected. On the contrary, more than 12 hours of light intake reverses the plant to the vegetative stage, or at worse, the plants become hermaphrodites, producing both female and male plants.

The hermaphrodite cannabis plant has the tendency to pollinate the rest of the crop, thus depriving you of unpollinated buds called sinsemilla with higher THC content.

Moreover, you also need to ensure the following factors during the flowering stage:

  • Warm temperature between 18C to 26C degrees.
  • The humidity levels should remain between 40 to 50 percent.
  • You need to select a higher light intensity, such as red spectrum light.
  • It’s vital to ensure a higher dosage of nutrients.
  • You must maintain pH levels between six and seven.
  • Water the plants as required.


In addition to that, you must shift the plants to the final larger pot before beginning the flowering stage.


Total Duration

The total duration of the flowering stage primarily depends on the strain type ranging from eight to 11 weeks.

Generally speaking, the flowering stage of the Indica strain lasts eight weeks and may go up to ten weeks. Similarly, the Sativa strains take around ten to 12 weeks, while the hybrid strains take six to ten weeks for complete development.


Indoor Flowering Stage

If you are growing marijuana plants indoors, you can either use full-spectrum LED lights or HPS lamps that offer a higher amount of photonic energy required for the development of buds.

Furthermore, you can sub-categorize the flowering cycle into three stages – initiation, mid-flowering, and late-flowering.



This sub-cycle lasts from one to three weeks during which the plants stretch and grow in size and length. Furthermore, the female weed plants produce the pre-flowers whose pistils resemble white hairs.

At the end of the third and final week, you’ll see the bud sites in the plant nodes, the area where the branches and the primary stem meet.

After two to three weeks, you’ll also be able to see the sex of the plants. It’s essential to remove the male marijuana plants after identifying them correctly.



The mid-flowering phases last from week fourth to fifth, where the buds grow in size while their pistils darken in color.



The buds begin to gain weight during the last weeks of the flowering stage. When you touch the buds, you’ll find them sticky and smelly. Hence, it’s a clear sign that you’ll harvest the cannabis crop very soon.

The pistils begin to show brown, cream, and white colors. Furthermore, the trichomes cover the pistils as they curl inwards. Lastly, you also need to focus on the changing colors of the trichomes as you can get an indication about when to harvest the flowering plants.



It’s a process of watering plants without adding any nutrients. This way, you can flush and remove the excess salt from the roots. Ideally, you need to perform flushing one or two weeks prior to harvesting.

On the contrary, the buds can develop a strong flavor and bad smell if you don’t flush them. As a result, the weed feels extremely harsh on the throat while smoking.


When to Harvest Cannabis Plant

The buds began to flatten around the eighth week of the flowering cycle. Furthermore, you can see that pistils and trichomes become mature and change their colors.

As a rule of thumb, the plants are ready for harvesting when the trichomes become transparent to milk color, while five to ten percent show amber color.


Scheduling Your Light Cycles for Better Yields

Let’s summarise the guide with the following bullet points:

  • The seed germination lasts for three to ten days and requires a light cycle of 16/8 with 16 hours of exposure to light.
  • The seedling stage lasts for two to three weeks with a light schedule of 16/8.
  • A cannabis female plant grows maximum in the cannabis vegetative stage, requiring a light schedule of 18/6. This stage lasts three to 16 weeks, depending on the strain type.
  • The flowering stage comprises initiation, mid-flowering, and ripening. Lastly, the best light cycle for the flowering stage is 12/12, while the process lasts for eight to 11 weeks.


Light Cycles for Auto-Flowering Plants

Autoflowering plants are produced as a result of crossbreeding cannabis with a day-neutral plant. As a result, the flowers no longer depend on the light and dark period; instead, they are based solely on time.

Furthermore, auto-flowering plants don’t require a photoperiod for transition into the flowering stage. Hence, the cannabis vegetative stage lasts around four weeks, and later the cycle automatically shifts to the flowering cycle.

The optimal light schedule for autoflowering cannabis is 18/6 to maximize the final yield at the cost of electricity. On the other hand, the 12/12 light cycle for weed minimizes the light exposure leading to lower yield.


Cannabis growth stages


Closing with the Weed Plant Stages and the Light Cycles

The key takeaway of the above guide is to utilize light schedules to ensure a successful flowering and better harvest.

All the female weed plant stages, including seedling, vegetative, and flowering, have different light requirements. The seedlings don’t require much light, while the vegetative plants require 18 hours of light. Lastly, weed plants need uninterrupted darkness for 12 hours to produce buds.

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