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Mastering Cannabis Vegetative Growth

Every stage of cultivating the cannabis plant comes with its own unique set of dynamics. This article addresses the cannabis vegetative growth stage (also referred to as the cannabis veg stage) and dives into the detail of what it is and how to unlock its potential on the way to growing bigger, healthier cannabis plants.

Before we start, it’s important to recognize that cannabis plants will behave differently, depending on which type of photoperiod (ie light sensitive) strain is being grown. 

The growth structure of mostly indica plants is different to mostly sativa plants (the former is shorter and more bushy), while hybrid varieties may display a combination of indica and sativa characteristics.

Cannabis strains explained visual


And then there are autoflowers, which behave very differently as a consequence of their automatic flowering clock, which means the veg stage lasts only 2 – 3 weeks. For the purpose of this article, therefore, the emphasis is on photoperiod plants.

The best advice for any grower hoping to master the cannabis vegetative growth phase is to grow from a high quality cannabis seed which comes with the provenance of good breeding history.  

Why is the veg stage so important for a cannabis plant?

Every growth stage of the plant is important, but what are the defining features of the cannabis vegetative growth segment of the lifecycle?

Well, this is the stage when the plant really takes off, filling out its structure with branches and healthy foliage growth to aid the process of photosynthesis, which is crucial to the nourishment of the plant. 

What are the key characteristics of the cannabis vegetative stage?

  • Root development
  • Rapid growth
  • Environmental adaptability
  • Structural flexibility
  • No bud development
A cannabis seedling view

What is the weed plant doing during the veg stage?

1) The plant is developing its infrastructure. This involves growing a thick stem to support numerous branches. It also involves growing the lush canopy of leaves to utilize the photosynthesis process and ensure plant health.  

2) The plant is developing a complex root network. Infrastructure development is not only upwards! Beneath the soil runs the extensive network of roots which is feeding the plant with water and nutrients. Strong roots form the route map to good plant health and a vital defence against disease. 

3) The plant is becoming a growth machine! A big, healthy plant produces big, healthy buds! During the cannabis vegetative growth stage, the plant’s energy is focused on rapid production of branches and nodes which are the points where buds will flourish during the flowering stage of growth. 

4) The plant is at its hungriest! Think of the weed plant as an athlete, training for the grand event, which is literally pumping out the best looking flowers it is capable of! The cannabis vegetative growth leg of that journey is the equivalent of an athlete stacking calories in the form of nutrients to give it that essential energy for the next stage.

5) The plant is the most adaptable in the veg stage. While in the germination and seedling stages a plant is fragile and needs tender care, once it achieves the vegetative state, it is capable of extraordinary behaviour! In the veg stage you can bend it, twist it, even break it and it will adjust and continue to grow – the perfect time for training!

cannabis plant roots
A snapshot of the complex cannabis plant root system in the veg stage.

What factors influence a successful cannabis veg growth stage? 

Creating the right environment for cannabis plants in the cannabis vegetative growth stage is key to producing a harvest bounty at the end of the flowering stage. By creating the optimum environment during the cannabis vegetative part of the plant’s journey cannabis plants have the capacity to grow between 3 and 5cm per day. So what should you be checking?

Get the light right in the vegetative phase!

At this stage of the plant’s life, cannabis loves strong light, with a minimum of 16 – 18 hours a day of exposure (although some growers argue that 24 hours light is the recipe for superfast growth, others argue the plant needs time to rest and this is a topic for debate). By maintaining the photoperiod of 18 hours light a day, a plant can theoretically live forever in the veg state. 

  • During the veg phase, plants benefit from light in the blue spectrum (around 400-500 nm), ensuring good leafy growth, while increasing the red in pre-flowering encourages bud growth.
  • It is always worth investing in LED lights which provide a fuller spectrum and researching the impact of PAR, photons and UV is also recommended. 

Caution:  

Check your distance! 

This is particularly relevant for growers using HPS lights, but applies throughout. 

  • Make sure that the space is not squeezed between the lights and the plant canopy beneath to avoid light burn.
  • On the flip side, make sure that they are not too far away from the canopy to promote plants to stretch towards the light (making them more spindly).

Get the temperature and humidity right in the cannabis veg stage!

A plant prefers a warmer temperature in the veg phase than in flower. The ideal temperature for the on-light period of a plant in the cannabis vegetative growth stage is 24/25°C (75 – 77°F), while the ideal temperature for the off-light period is 17/18°C (62 – 64°F). The humidity level should be around 60 -70%.

This is easier to control indoors, although problems do arise in a summer grow room. Outdoors it is inevitably more difficult to control the environment and excess heat and especially when growing in greenhouses and under plastic in polytunnels.  

Caution:

  • Heat stress (which tends to occur when the temperature is over 30°C/86°F) to vegging plants will impact on health and reduce the harvest capacity of the plant. On the flip side, cold stress kicks in when the temperature drops below 12°C/53°F)
  • Stagnant air should be avoided, by ensuring good ventilation and using fans to keep the air circulating.

Ensure the nutrient levels are right in the cannabis vegetative window 

Inevitably plants need nourishment to achieve their growth potential. They are particularly hungry during the cannabis vegetative growth stage and require feeding with essential nutrients.

The most significant come in a pack, known by the acronym N-P-K (Nitrogen-Phosphorous-Potassium), and are at the core of any off-the-shelf fertilizer solution for the veg stage, but other nutrients also play a role. 

  • Nitrogen (N): Giving plants that essential leafy growth, and stimulating growth cells through the formation of amino acids and proteins. 
  • Phosphorus (P): A contributor to all round growth, phosphorous also helps develop roots and transfer energy around a plant.
  • Potassium (K): A stimulant for various metabolic processes, including photosynthesis and water uptake. 
  • Calcium (Ca): A vital component in the structure of a plant’s cell walls, building resistance.
  • Magnesium (Mg): A nutrient which plays a key role in the photosynthesis process.
  • Sulfur (S): Helping to create new plant cells is helps to form amino acids and proteins. 

Caution: Get the balance right!

  • Over or under administration can cause issues which manifest in the plant’s appearance (most obviously in leaf color changes and wilting plants). 
  • Excess, deficiency, lock-out are the most common nutrient issues that can be diagnosed and solved. 

Consider the pH

Check and maintain the pH of your growing medium (soil or hydroponic solution) during cannabis vegetative growth. A pH of around 6.0-7.0 is suitable for most cannabis plants during the vegetative stage, ensuring nutrient absorption.

Consider using CO².

Although CO² adds more value in the flowering phase, many growers also value its contribution in the cannabis vegetative growth stage. Natural air exchange should generally provide enough CO2, but some growers provide additional CO² while plants are in the vegetative state.

The veg stage is the perfect time to train cannabis!

We have already discussed how a plant is a growth machine during the cannabis vegetative phase. In this mode, it just wants to grow and grow, no matter how you try to restrict it! For this reason, this stage is when weed plants can be trained.

There are many ways to train a plant – from LST (Low Stress Training) to HST (High Stress Training) to SCROG (Screen of Green) and SOG (Sea of Green), Topping and Fimming and Mainlining.

You can find all the answers in this comprehensive guide to growing cannabis with these awesome grow techniques

Potential issues in the cannabis veg stage

In an ideal world, the period of cannabis vegetative growth stage will be punctuated by lush green canopies and generous branch development, setting the stage for the grand finale in the form of flowering and harvest. 

However!… At some point, every grower will encounter an issue with their vegging plants. Problems can include:

  • Nutrient deficiencies.
  • Pests and diseases. 
  • Watering issues.
  • Stress.

This handy reference guide to the most common cannabis growing problems and solutions provides a troubleshooting handbook for cannabis vegetative growth stage cultivation issues in both indoor and outdoor environments

Cannabis Vegetative Growth Stage Timeline

If growing outdoors, the timescale is dictated by the sun so the cannabis vegetative growth stage can last for up to three months.  

The following reference guide details the key stages of the cannabis veg process in an indoor environment and gives a general idea. However, it is only general – plants respond to nature as much as they do to nurture, and factors such as genetics and environment can make a difference.

  • Day 15 – 28: Transition to vegetative growth. The plant will begin to rapidly develop, growing upwards with 4+ sets of leaves. Beneath the ground growth will focus on root development.
Cannabis vegetative growth stage plant in grow tent
A plant in early veg stage
  • Day 29 – 42: The plant starts to enter a period of vigorous cannabis vegetative growth. At this point it will be hungry for nutrients and should be monitored for signs of deficiency. This is also the period when training can be conducted without fear of damaging the plant. 
  • Day 43 – 56: The plant will continue with its growth, becoming bushy and filling out with lush green foliage while developing branches. Good ventilation and keeping an eye on humidity issues is advised during this stage. Some pruning can help with management and open up the structure to allow light to penetrate to bud sites in the next phase.
  • Day 57 – 70: The pre-flowering stage is about preparing the plant to transition from the veg stage to the flowering stage. A reduction of light towards 12/12 (light/dark) simulates natural light conditions.
Cannabis plant in pre-flowering stage

It should be stressed that throughout the vegging stage, plants need to be frequently checked and monitored for signs of issues (don’t forget those ones right at the back!). An issue can usually be dealt with if caught at an early stage. 

** A good bit of advice to avoid plants developing hermaphrodite traits in flowering, is to lollipop the lower branches. 


The transition from vegetative stage to flowering stage

When to Transition to flowering?

Getting the timing right is crucial. Do it too early and the final yield may be limited. Do it too late and your grow room will be a jungle! Most growers will transition after 4 – 6 weeks of the veg period.

For the transition from the cannabis vegetative growth to flowering stage the best indicators of the right time to make the switch are:

  • Breeder’s recommendations: Sometimes strain descriptions will give advice on recommended veg time.
  • Physical signs: Most growers will take into consideration their grow space, switching to flowering when plants are half their desired size.

When the transition takes place, the light cycle is changed from the 18 – 24 hours of light to 12/12 (light/dark). If using LED lights with different spectrum options, then moving to the red spectrum encourages flower development.

The Takeaway!

The cannabis vegetative growth stage is as important as any of the other stages in the growth cycle of the weed plant. It’s the time for bulking out and stocking up on the essential energy for the showpiece finale! 

Due to its vitality during this growth stage it is a more forgiving phase in many ways because the plant just wants to grow! The biggest challenge is to manage that growth within the confines of a grow space and to make sure it has everything it needs.

To avoid issues, it’s important to keep the nutrient schedule in check and also to carefully monitor the progress of the plants. This is the only way to deal with any issue before it manifests as a bigger problem.   

A healthy cannabis vegetative growth session is the best platform a plant can have to springboard into the flowering stage. Healthy growth will provide it with the infrastructure above and below the soil to support the abundance of bud sites which will develop into that glorious flower show at the conclusion of its life.  

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