Cannabis Light Schedules For Vegetative & Flowering Stages

Cannabis Light Schedules For Vegetative & Flowering Stages
July 17, 2019

Cultivating cannabis is a costly and challenging process. But, when done right, the reward of fragrant and flavorful flowers more than makes up for the time and money invested. On the other hand, charging head first into the practice without proper research will lead to a less than ideal harvest. Hence, in-depth insight into the aspects of growing high-yielding strains must be observed.

One such aspect is the light schedules for proper cannabis cultivation. Light cycles for weed differ for different strains, location, and growth stages. Thus, it is crucial to differentiate between the amount of light and darkness a plant needs. If handled correctly, a bountiful harvest will most likely be on the horizon.

The Science Behind Light Schedules

Cannabis Plant Under LED Light

Plants rely on light for their food and sustenance. Hence, detecting light is crucial to their survival. It is the job of Phytochromes, the blue-green pigments found in plants that act as light detectors. During a flora’s growth period, these photoreceptors are found in high concentrations but are less apparent during nutrient acquisition.

Compared to other pigments found in plants, Phytochromes are minuscule. Typically, the only way to observe it is through a spectrograph, an instrument that separates light by its wavelength. However, regardless of its size, these light receptors hold an essential role in a plant’s overall growth and development.

Apart from detecting light, Phytochromes are responsible for inducing seed germination, leaf expansion as well as regulating the flora’s circadian rhythm for both its vegetative and flowering phase. As such, these receptors are often manipulated to control growth and inhibit over-blooming or early harvests in cannabis cultivation.

Red To Far-Red Ratio

Cannabis has two central light receptors: Phytochrome Red and Phytochrome Far-Red. The plant switches between the two depending on light conditions or the ratio of red light to far-red light (R:FR) it detects.

Red, orange, yellow, green, blue, indigo, and violet are the seven varying colors the sun emits. The hues on the far end of the spectrum are called the Far-Red lights. These tones play a pivotal role in the health and growth of the plants. Meanwhile, the red light allows floras to grow strong, colorful, and to produce fruits and flowers.

Apart from the mentioned out-turns, every color induces other effects from the plant that can encourage development and an enormous yield. To get the preferred response, though, understanding the light spectrum is not enough. The knowledge must also be applied with the right balance of Phytochrome Red and Phytochrome Far-Red are at the right time and duration.

Light Schedules To Ensure High Yield

A proper amount of light is essential in cultivating high-yielding strains. Without a precise schedule, cannabis plants will not grow to their full potential. Hence, it is imperative that floras receive the correct light cycle per growing stage.

Cannabis has two main phases of growth. During the vegetative stage, the stems and leaves develop. Then, the plant enters the flowering period that commences the buds to bloom.

Photoperiod Strains

Photoperiod refers to the amount of light given to an organism within a 24-hour time frame. Such strains are called “long night” or “short day” plants. In cultivation, this means that it must be given extended periods of darkness to induce flowering.


There is an inherent advantage to growing indoors. Unlike in the outdoors, environmental factors such as temperature and lighting can be easily managed. In this regard, controlling the light schedule is much simpler than working with outside conditions.

Cannabis Indoor Controled Environment

Vegetative Phase

During the vegetative stage, indoor cultivation is much favored. It ensures that the preferred growth of the plant is achieved by merely manipulating the hours of light.

For a flora to attain its maximum potential, it must be exposed to 18 (18/6) or 24 (24/0) hours of light for 4 to 8 weeks. The long periods of illumination allow the plant to grow as huge as possible. Also, a controlled setup affords to extend the phase for as long as desired by just maintaining at least 13 hours of incessant light exposure.

Do note, however, that prolonged vegetating will cause the cannabis to increase in size continuously. Hence, extending is only appropriate for grow areas with ample vertical space and is not ideal for keeping variants compact.

Flowering Phase

Typically, once the cannabis reaches a suitable size, the budding stage is induced. To do this, the nearing of winter must be mimicked by extending the length of darkness to 12 hours. Otherwise, the plant will stay in the vegetative phase. Moreover, such pattern must be followed religiously until harvest rolls around or the plant may go back to vegetating.


Growing in the outdoors puts a plant at the mercy of nature. Ergo, it is imperative to avoid erratic or extreme temperatures and to keep an eye for any weather changes. For a successful open-air cannabis cultivation, staying alert and timing is of the essence.

Cannabis Cultivation

Vegetative Phase

In general, most start the vegetative phase indoors around March or April to ensure that the plant develops to the preferred size without natural delays. Then, move it outdoors by the time May or June rolls around. Such a technique allows the flora to develop appropriately and be robust enough to face the whims of the outside world.

If growing in optimal settings, putting the flora outdoors during the vegetative phase is fine although still extremely risky. However, it must be moved indoors urgently in case of any temperature drop.

Flowering Phase

When placed outdoors, cannabis will enter the flowering phase without assistance. It does not mean, though, that the plant will reach harvest without supervision. Proper maintenance and care must still be exercised. For instance, a streetlight or porch light can easily disrupt their crucial 12-hour darkness period. If this happens, the plant is likely to deviate from flowering and go back into the vegetative stage.

Auto-Flowering Strains

Auto-flowering strains are bred from a subspecies of cannabis called ruderalis. Plants from this category do not depend on light cycle to induce flowering. Additionally, it has a relatively shorter vegetative phase (2-4 weeks) compared to photoperiod strains (4-8 weeks).

24-Hour Lighting

Autoflowering strains do not need darkness to finish vegetating or flowering. Some argue that a 24-hour light schedule is ideal for these plants as a full day of photosynthesizing means more energy to create food. And, more food for the flora creates fatter buds.

18-Hour Lighting

While many use the 24-hour light schedule, it is not without flaws. Not only does it rack up electricity bill, but it also does not give the plant enough time to rest. Additionally, using such a method in a dry or warm climate area will increase the heat in grow room or box. Besides, the increase in yield is not much. Thus, using an 18-hour approach will allow for recuperation, lower energy bill, and cooler temperatures.

Achieving High-Yielding Strains With Lighting

Cannabis growth is dependent on the amount of light it is exposed to in each stage. Hence, going forth with a limited understanding of light schedules will result in an early harvest or, worse, a dead plant. It is imperative to know the proper application of light and darkness in cultivating the plant. Only then will cultivation result to a high yield.

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