How To Grow During The Vegetative Stage of Weed

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The vegetative stage of weed is the part that comes between the seedling and flowering stages. This is the time when the plant is only growing leaves and branches and gains most of its size. In ideal conditions, weed plants are known to double in size roughly every two weeks while vegging. So how do you manage such growth to maximize the quality and quantity of your marijuana yield?

In this article, we will dive deep into the science and art of vegging cannabis. It will cover all the basic principles that growers need to know about the vegetative stage of growth in cannabis.

What is the veg stage?

As mentioned earlier, it is the stage during which the cannabis plant grows its main structure. This means growing lots of fan leaves, secondary leaves, and branches. The plant grows larger and taller every day. The vegetative stage weed plant is trying to grow as big and strong as possible before switching to the flowering stage. By taking good care of your plant during this stage, you can prepare it for a bigger yield and top-notch bud.

Why is the vegetative stage of weed important?

The veg stage of cannabis is important because a weak plant cannot produce top-shelf buds. That is the endgame that most weed growers are after. To create a strong robust weed plant you need to be take care of it, all the way from seed to harvest.

The veg stage is where the plant does the bulk of its growing and structuring. It is also the time when you can apply special growing techniques to increase yield by carefully guiding the growth of the plant. Hence, the vegetative stage of growth is like the foundation period of the weed crop.

With a poor veg stage, the flowering stage will suffer and yields will be lower, so lets begin laying the foundations for a solid start to your grows.

When does the vegetative stage start?

Cannabis enters the vegetative stage as soon as it grows its first few nodes. Before this, it is essentially spending more energy developing its root structure. A large and healthy root structure will always lead to a large and healthy plant.

Once the initial root development has reached a level of maturity, the plant automatically starts to explode into growth above the soil. This stage will start within 3 to 4 weeks from germination.

When does the veg stage start for autoflowers?

Autoflowering strains are no different from other cannabis strains regarding vegging. The only difference between autoflower strains and regular strains is that they switch to flowering mode automatically around 3-5 weeks into their veg stage. They then continue to gain size as they develop flowers.

For this reason, autoflowering strains need extra care when they are vegging because the duration is fixed and short lived, therefore you want to avoid anything that might stress your plants.

Regular photoperiod strains can stay in the vegetative phase as long as you want and will only begin flowering once the light cycle is flipped to twelve hours of light and twelve hours of dark. This gives growers time to fix mistakes if they need to. There is no such option with autoflower strains.

The same also holds true for all outdoor grow operations because they begin flowering based on the natural shortening of daylight hours as winter draws closer.

How long do weed plants stay in the vegetative stage?

Indoor growers can maintain their plants in the vegetative stage indefinitely because they can control the light cycle manually. However, most plants have grown all they need to by the time they hit weeks 6 to 10. Most growers will switch to a flowering light cycle depending on the size of the plant rather than the age.

Since the plant will double in size during the flowering phase, most decide to switch when the available growing space is about half occupied.

Vegetative stage length outdoors

The length of the vegetative stage of growth of cannabis plants outdoors can vary with geographical locations, seasonal variations, and strains. However, it is between 4 to 16 weeks long depending on the length of long summer and pre-winter/autumn days. So be sure to time your grows based on the seasons in your region as there is no one size fits all approach to outdoor cannabis growing.

outdoor grow during the vegetative stage of weed
Outdoor cannabis grow during the vegetative stage

How to speed up the veg stage of growth?

It is possible to speed up the veg stage of growth for cannabis plants if grown indoors with artificial lights. Growers can do this by increasing the number of light hours. The normal light cycles for cannabis veg stage indoors is of 14 to 18 hours of light. This provides a standard amount of light for the plant. However by changing the light cycle hours to 20 hours of light and just 4 of dark, the growth can be sped up beyond its natural cadence.

However, this also means the plant will use up nutrients much faster than normal. So, a close watch must be kept on the nutrient levels. It also means that with very little hours of darkness the plants are more likely to become stressed. If you attempt to speed up the veg stage of your cannabis grow, be sure to closely monitor your plants for any signs of heat stress.

How long does it take to grow weed?

Cannabis plants vary in how long they take to grow from seed right the way through to harvest. A typical grow takes 3-4 months from seed to harvest. This timeline can vary based on the strain and growing conditions, but it usually involves a vegetative stage of 2-3 months, followed by a flowering stage of 6-10 weeks.

Key rules to follow for a healthy vegetative phase

As with any plant, cannabis depends on various factors to achieve optimal growth and health. Hence it is important to focus on and monitor certain key areas of the plant’s growth requirements.

  • Lighting – Make sure that you have adequate lighting if you are growing indoors. For outdoor grows, it is important to grow in an open area where nothing can block the daylight from reaching the plants for as long as the sun is up. Be sure you time your outdoor grow with the seasons, otherwise you could end up with a much smaller yield if you germinate your seeds later.
  • Nutrition – Plants in the vegetative growth phase need a lot of nutrition to produce all of the leaves and branches. Underfeeding can slow down the growth or stunt it, but overfeeding can also have similar effects. So, balance is key. It is smarter to err on the side of underfeeding rather than overfeeding. Always check for signs of over or underfeeding based on how the leaves look. Dark green leaves curling downwards are a sign of overfeeding, and yellowing, wilting leaves are a sign of underfeeding.
  • Water – Cannabis always needs a moderate amount of water in the soil to continue growing rapidly during the vegetative stage. So, maintaining a close check on the moisture content in your soil will be helpful. Also, remember that overwatering is just as likely to kill the plant as underwatering.
  • Airflow – Particularly for indoor growers maintaining a good level of airflow around your plants is vital to prevent issues such as mold developing. When growing indoors it is advisable to install a fan that will swivel and mimic the natural outdoor wind flow throughout the growing area. A moderately strong air current will result in stronger, healthier plants.
  • Pest control – Check the fan leaves and the hidden areas of your plants daily for signs of fungal, bacterial, and insect-related health problems. Maintaining dry foliage and slightly damp topsoil is a good way to control infections and infestations. Beginners might also want to consider maintaining a mostly dry top layer of soil because moisture attracts bugs.
  • pH level – Continue maintaining a soil pH of around 6 to 6.5 for the best growth conditions. This is the pH at which the soil microbiome thrives and helps the plant convert and absorb nutrients easily. An out-of-whack pH balance in the soil will cause the cannabis plant to falter in its growth rate and health. Use professional pH and PPM meters to understand your growing medium’s pH and nutrition levels. These measurements will help you prevent costly mistakes and show the problem area sooner rather than later.

What is the best light cycle for the veg stage?

Cannabis plants will continue vegging as long as the daylight hours are continuously over 12 hours. So, most growers will maintain a light cycle of 18-6, meaning 18 hours of light followed by 6 hours of total darkness. Growers can tweak the growth rate by providing more light hours and fewer dark hours.

Some growers are even known to run their lights constantly, putting the plant in a state of perpetual growth for a few weeks. This is an advanced method and should be carefully controlled to prevent overheating loss of moisture and depletion of nutrition levels due to the rapid growth rate.

Using the 24 hour light cycle method is most commonly used with autoflowers, although in my experience I have seen better results from 18/6 and 20/4 as the dark period allows plants to recover from any stress they have experienced.

cannabis plants during vegetative stage of growth under 18/6 light cycle
cannabis plants during vegetative stage of growth under 18/6 light cycle using CFL lights

What is the best temperature for the veg stage?

A study was done on the propagation of cannabis for clinical research and it found that the optimum temperature for cannabis plants during the vegetative stage was between 25 to 30 degrees Celsius. That is 77 to 86 degrees Fahrenheit. Since indoor grow operations need large lights to grow cannabis, it is important to manage the heat output of these lights to maintain a sweet spot temperature that is usually somewhere in the middle of the acceptable range of temperature.

This will vary depending on location, local climate, strain, ventilation, etc. So, it is good to get used to a new growing setup before trying out a large crop size.

It is a good idea to carry out some research into the different types of grow lights instead of going for the cheapest or most powerful option. HID lights although low cost and powerful, produce a lot of heat. If used in warm humid conditions it could overheat your grow room. Therefore, if you live in a hot country it may be a better idea to use LED lights that give off much less heat and can still produce the same yields.

What are the best nutrients for the veg stage?

Growth stage cannabis plants will require a lot of nitrogen (N), phosphorus (P), and potassium (K) to develop, and it also needs to be supplemented with calcium and magnesium. So, growers will use the typical NPK fertilizer and then choose their own Calcium/Magnesium supplement to boost it further. A bit of sulphur is also a healthy addition to the mix.

These secondary nutrients promote things like root growth, stem size, strength, pliability, and leaf health. Just remember to make a study of the ratio in which to administer them to the plant. Some trials over a few smaller crops should give you an idea of what is appropriate for your unique growing situation and preferences.

You can choose to use purely artificial nutrients, organic, or a mix of both.

When to start training during the veg stage?

The vegetative stage is the best time to train your cannabis plant to grow in a way that efficiently utilizes available light and air. This is typically optional in outdoor growing operations because the sun provides abundant light from every direction.

However, in indoor grow areas, light is limited and is usually distributed horizontally. Since the cannabis plant tends to grow vertically like a Christmas tree when left to themselves, growers need to use high and low-stress training techniques to spread out the canopy evenly across the available space.

High-Stress Training

Also known as HST, the best time to apply high-stress techniques, like topping or FIM-ing, is after the plant has grown to at least five nodes. That is when the plant has at least five levels from where branches come out of. Then you can cut off the topmost node (fifth or higher) to “top” the plant. The plant will take a few days to recover, and two new branches will grow horizontally from the cut-off node.

Continue to do this over a few weeks to get the best results and do give the plant plenty of time to recover and grow. Read more on HST training techniques here.


pruning cannabis fan leaves during the vegetative stage of growth

Cannabis defoliation is another moderate to high-stress training technique where fan leaves are pruned off to allow more light and air to enter the innermost areas of the plant. The cannabis plant always produces extra fan leaves to insure against leaves lost to pests and herbivores. Since this is not an issue indoors, growers manually chop off leaves to give the plant more energy to grow in size.

Start from the bottom up and defoliate gradually over weeks. Allow rest periods of a few days between each session. Be careful not to prune too much because fan leaves are the energy generators of the plant and losing too many can slow down growth or even kill the plant when taken to an extreme.

Defoliating autoflowers however can be risky due to their shorter growth times. It can be done but too much stress can cause stunted growth so using lower stress training techniques are often preferred.

Low-Stress Training

Also known as LST, this simple but effective technique involves the flattening of the canopy by bending the topmost parts of the plant to make them level with the rest of the foliage. This is usually done using plant wire ties or a trellis net. This creates an even distribution of light and airflow. This allows for greater yield and even growth. The bent branches adjust themselves after a day or two and start to grow in tandem with the rest of the plant towards the light source. Read more on LST training techniques here.

cannabis plants during vegetative stage undergoing LST training
cannabis plants during vegetative stage undergoing LST training

When should you start flowering indoors?

The best time to start flowering indoors is when your plant has filled up about half of the available growing space. Since the plant will double in size during the flowering phase, it will need leftover room to grow at the end of the vegetative stage.

Most growers choose to switch to flowering around the 7th or 8th week. However, this changes based on individual preferences and unique situations. So, practice growing in small batches to understand all the nuances before embarking on a large operation.

What’s Next?

We hope this answers all your major questions about the vegetative growth stage in cannabis plants. Your weed plant should be ready for flowering in about 7 to 8 weeks. Check out our flowering stage article to learn more about what to expect and the best practices.

Do you have more questions about the vegging stage? Ask us in the comments section.


Chandra, S., Lata, H. and ElSohly, M.A. (2020). Propagation of Cannabis for Clinical Research: An Approach Towards a Modern Herbal Medicinal Products Development. Frontiers in Plant Science, [online] 11. doi:10.3389/fpls.2020.00958.

Joe Musgrave

Joe Musgrave is a keen 420 blogger who writes about all things cannabis. After harnessing his green thumbed skills through years of working on cannabis farms, Joe now shares his knowledge with the rest of the online 420 community.

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