The Vegetative Phase Of Cannabis Cultivation

The Vegetative Phase Of Cannabis Cultivation

Steven Voser
Steven Voser

The vegetative phase in cannabis plants’ life cycle is vital as plants use it to prepare for an optimal flowering period. When caring for your plants there are several factors to consider during that stage, such as light cycle, watering, nutrients, and more, so every grower should have a good idea of how to respond to their plants’ needs so they can thrive. Use the guide below to discover the intricacies of the vegetative phase of the cannabis life cycle.

The vegetative phase, colloquially known as the “veg”, begins from the moment seedlings rise to the surface until the beginning of the flowering phase. During the vegetative phase, cannabis plants grow from tiny seedlings to mighty trees. Fan leaves develop, absorbing light for photosynthesis, which provides the plants with required energy.

The stems become thicker, supporting the structure of the plants and protecting them from windy environments. Different strains will exhibit different growth patterns during the vegetative phase. Some plants develop thick stems, others are thinner. Some strains, like autoflowering varieties, will become quite short, spanning between about 30-100cm in height.

Sativa-dominant, photoperiodic strains, however, can reach up to 400cm. Depending on the strain’s genetics, the amount, shape, and size of the leaves will also differ. For example, indica varieties evolved in harsh environments between the Hindu Kush mountain range and desert climates; as a result, they developed a “wide finger” leaf structure as a defence mechanism to retain water and protect buds from the blazing sun. On the other hand, sativa strains develop “narrow finger” leaves, which help them to respire in the tropical and humid environment where they evolved. Let’s check out the fundamentals behind a vigorous and strong vegetative growth phase for cannabis plants.

Fundamentals and logistics

Fundamentals And Logistics

The vegetative stage should be seen as the foundation on which our beloved buds can flourish. When the plants grow tall, strong, healthy, and resilient, it will provide the buds with an opportunity to maximise their potential and quality. Vegetative growth can be modified in accordance with the physical environment for logistical purposes. The stems can be bent and trained to work with the limitations of smaller indoor settings.


First, let’s address the fundamentals of vegging plants outdoors. One should choose the appropriate strains for the climate in which the cannabis plants will grow. As a rule of thumb, sativa-dominant strains thrive in tropical climates, while indica-dominant strains thrive in dry and hot environments. One can use the Köppen climate classification as a guide to choose the right cannabis variety. Outdoors, we're dealing with a bunch of insects. Strains which are resilient to pesky pests are ideal. Those strains that develop plenty of trichomes are a good choice because they help control plant temperature, and terpenes act as an insect repellant. One could also use biological insecticides during the veg if necessary.

Depending on the size of the plant, support may be required. Some sativa strains grow like normal-sized trees during the vegetative stage. Even though one doesn't have spatial limitations outdoors, the branches may snap under their own weight if the plants are too tall. Tying the branches may be a smart move. One could also use topping techniques, which creates more bushy and stable plants.

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In most indoor operations, there is limited space for plants to veg. Indoor growers often prefer indica and autoflowering varieties because they’re relatively short. Cannabis plants with classic sativa traits are difficult to grow as they take over the grow space like those plants in Jumanji. Sativa plants can stretch up to 3x their height after they’ve been put into bloom. To control height during the vegetative phase in indoor environments, growers use SOG and ScrOG techniques to train the plants to grow in specific directions. These techniques are quite advanced; novice growers should get a couple harvests under their belt before attempting these methods.

Stage duration and light cycle

Stage Duration And Light Cycle

Vegetation outdoor

Outdoors, one needs to begin the vegetative phase during the ultimate time frame. If one’s planning to vegetate plants for 5 months, they should be planted 5 months before the fall season begins, because that’s around the time photoperiodic cannabis plants start flowering.

For example, if the fall season begins in August, and one’s planning to vegetate the plants for 5 months, the plants should be sown in March. The duration of the vegetative phase greatly depends on the strain and preference. Generally, when growers want massive plants, they’ll leave the plants in veg for a long time; if short plants are desired, they’ll be planted closer to the beginning of fall. Autoflowering strains, which derive from Cannabis ruderalis genetics, have a very short vegetative phase due to their development in cold climates. Therefore, they should be planted during the 2 months with the most hours of sun as this will allow these short and fast-growing plants to thrive.

Vegetation indoor

Indoor plants don’t depend on outdoor seasonal changes to begin flowering, therefore, one can begin the vegetative phase whenever and keep it going for an extended period of time. Just like in outdoor conditions, to produce massive plants, one should keep them in the vegetative phase for a longer time. During the veg, indoor-grown cannabis usually receives 18 hours of light and 6 hours of complete darkness.

There is a general consensus among cannabis growers that the 18-6 light cycle produces best results during the veg. The 18 hours of light signals to the plants that it’s spring and summer time, telling them to increase in size. Indoors, growers can keep the plants in the vegetative phase for a long time by maintaining the 18-6 light cycle.

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Mother plants (cannabis plants from which clones are taken) are not allowed to go into the flowering phase, so they're maintained indefinitely in the vegetative phase. Indoors, autoflowering varieties are often subjected to prolonged light hours spanning between 20-24 hours per day. That’s because autoflowering varieties are not photoperiod-dependent. It's not possible to manipulate the duration of their vegetative phase because their genetic "veg clock" is set after they rise to the surface.

In the greenhouse

Greenhouse cannabis gardens use sunlight as a source of energy for the plants, which means that they fall under the “outdoor” category. However, greenhouses provide growers with more control over light duration; additional lamps can be placed to keep the plants in veg longer while special covers can be used to blot out the sun to shorten the period.

Watering during vegetation

Watering During Vegetation

In the beginning of the vegetative phase, one doesn't need to water the plants often because small plants only absorb trace amounts. It's not possible to say how often the plants should be watered in detail because water absorption greatly differs between various growing media. One should keep the plants between being underwatered and overwatered, leaning more to the underwatered side. Overwatered plants are almost a lost cause while underwatered plants can be saved by simply replenishing the source. In this case, less is more. The water temperature should be around 20ºC.

Nutrients during vegetation

Nitrogen! The main ingredient which cannabis plants require during the veg is nitrogen. The N-P-K ratio (nitrogen-phosphorus-potassium) should be around 2-1-1, however, growers have different preferences and recipes. As a rule of thumb, when the leaves maintain a healthy green colour and don't fall off, the levels are just right.

Best grow room circumstances for vegetation

Best Grow Room Circumstances For Vegetation

Lighting: The best lights for the indoor vegetation phase are LED and HPS lamps. CFL lights can be used in smaller operations.

Temp: Outdoor plants can handle hotter temperatures up to 38ºC when the roots go deep into the cool ground. The perfect temperature for indoor plants spans between 21-29ºC. During the night, the temperatures should be slightly cooler, between 17-21ºC.

Humidity: During the vegetative phase, cannabis plants can handle higher humidity levels. Around 60% RH is recommended.

pH: The pH levels should be around 6-6.5 for soil-grown cannabis. For hydro, 5.5-5.8 is optimal.

Ventilation: Air circulation is necessary during the veg; both indoor and outdoor growers need to provide the plants with a gentle breeze for them to inhale CO₂, and exhale O₂.

Sex of plants

6  Sex Of Plants

One can determine the sex of cannabis plants during the late stages of the vegetative phase. If pollen sacs are spotted, they’re male plants, which need to be removed if high-quality buds are desired. When the females become pollinated by males, the plants focus their energy on creating seeds rather than THC.

When the males are removed and only females remain, one still needs to inspect the plants for any banana-shaped pollen sacs, which can develop on female plants due to stressful conditions. When detected in time, these pollen sacs need to be surgically removed without letting the pollen escape, as this could ruin the entire crop.