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1. Phase: Growing phase - vegetative phase 2. What happens in the vegetative phase?3. What does the vegetative phase mean for the plant?4. What are the ideal conditions for the vegetative phase?5. Why is a good start important?6. What to look out for in the vegetative phase

Phase: Growing phase - vegetative phase

The vegetative phase is one of the phases that a cannabis plant goes through. The period begins after germination of the seed and ends in the flowering or generative phase.

What happens in the vegetative phase?

Plants will not stop growing right away once the generative phase has arrived. During flowering, a plant can still grow substantially in size. How much the plant still grows during this period varies and depends on the species. The length of the vegetative phase is determined not only by the species but also by the condition of the plant. Autoflowers, as the name suggests, stop their vegetative phase when they reach maturity. They need, under the right conditions, about 3 - 5 weeks for this. Most growers who grow autoflowers indoors do so for the entire life cycle on 18 hours of light. After germination the first leaves form, these are lob leaves. The lob leaves are round and have no serrations yet. The light that these small leaves absorb is converted into energy for the plant. With this energy the plant is able to take up nutrients from the soil. This is called photosynthesis. Three things are important for this: light, air and water. The light and the carbon dioxide (CO2) in the air ensure that the nutrients absorbed by the plant through the water are converted into glucose. Glucose is a sugar that causes cell building in the plant. Building up the cells is plant growth. Therefore, it is important to place a seed that has just germinated in a Spongepot or in a coffee filter into the soil or other medium as soon as possible in order to absorb nutrients. After the lobe leaves comes the first set of leaves with the serrations that are characteristic of a cannabis leaf. The first set of serrated leaves has only one leaf. Or finger, whatever you want to call it. The set after that gets three leaves, then five leaves and so on. If conditions are ideal and the plant is comfortable in its environment, leaves can grow with as many as eleven fingers.

What does the vegetative phase mean for the plant?

A good start is half the battle. Also when growing cannabis. This is why the growth phase is just as important as the flowering phase. Especially when growing indoors. You don't want to pregrow for too long or the plant will outgrow its tent. But you also do not want a growth phase that is too short. The plant will then have too little time to make nodes. These are the branches on the plant from which it will produce side shoots. The more side shoots the more side branches will grow to form buds. And more buds is a higher yield. So it's not about the size of the plant itself, but more about how many buds you can get on one plant. In a grow tent this is important because of the limitations of the size of the tent. The trick then is to let the plant grow and create as many points per surface as possible where the buds will form. With the different training techniques you can grow a plant that produces many flowers but still remains small. The plant grows, the leaves have five fingers or more, the side shoots grow into twigs. But under the ground the plant also grows. A healthy plant is as big under the ground as it is above the ground. As a plant grows, the root system grows even more. By nature, a cannabis plant has one main root, also called a taproot, from which the side roots will grow. With a cutting, it's a different story. The underside of the cutting then acts as the main root and from here only side roots grow. The side roots branch, these branches also branch again and so the root system grows. On all the roots grow tiny hairs, these are called root hairs. The tiny hairs increase the root surface and, by means of the water, extract the nutrients from the soil. The roots pass this on to the rest of the plant.

What are the ideal conditions for the vegetative phase?

A good vegetative phase is the basis for the start of a good generative phase. The flowering phase in which the plant generates flowers. What the plant needs to grow is the same for an outdoor crop as it is for an indoor crop. The trick is to give all the factors in the right proportions to the plant. Because of the difference in environment, indoors or outdoors, there are also different aspects to take into account.

Indoor cultivation

Indoors you grow in a grow room or tent. This means that for almost the entire growing period you have everything under control. With a cycle of at least 16 hours of light and 8 hours of darkness the plant remains in the growth phase. As a rule 18 hours of light is used to prevent stress and premature blooming and to reduce power costs. When you switch to 12 hours of light and 12 hours of darkness, the plant moves into the flowering phase. You can extend the light duration to 24 hours yourself. Because the more photosynthesis there is, the faster the plant will grow. If more photosynthesis takes place, you will also have to supply more air, in this case CO2, into your growing space. The capacity of the suction is then of great importance. Because of the explosive growth of the plant due to the increased photosynthesis you will also have to give it more water and more nutrients. The more attention you pay to the top, the more attention you have to pay to the bottom. This is how you keep the proportions even. To do this as well as possible, it is advisable to invest in equipment to measure and control temperature and humidity. A PH and EC meter are also advisable to purchase so that the plant can properly absorb the nutrition. Or to prevent salt build-up between the root hairs that impede the plant's absorption of nutrition. If you are growing with Biotabs, you do not need to measure the PH. This nutrition is adjusted to tap water.

Outdoor cultivation

With outdoor cultivation there is little to regulate. The sun, rain and wind take over. The sun shines or it does not shine. There are many or few clouds. Strong winds and rain can cause damage to the still growing plant. Snails and other animals see the plant for a rich meal. But also pests and diseases lie in wait and can cause a lot of damage. When growing outdoors it is usually a matter of protecting the plant against these dangers throughout its life cycle and promoting the plant's own defense mechanism. Placing companion plants also helps well against pests and disease. These are other plants such as Chamomile and Lavender. Plants with a scent and a color stop or even chase away predatory insects. In doing so, they attract friendly pollinators such as bees. Lavender covers up the smell of cannabis and chamomile is great for making tea. There are also agents that you can spray on the plant to protect it, but do not use them if the plant is already blooming. The plant-eating critters do not like drafts. Therefore put outdoor plants in a place in the garden where there is a little wind. Removing a few large leaves here and there also creates more ventilation.

Why is a good start important?

A good flowering starts after a good growth phase. Growth starts well when the seedling has germinated successfully. Thus, each phase is important for a good harvest. To get solid buds, you also need a solid plant. As mentioned earlier, a plant above the ground is just as big as below the ground. So growing the plant is also growing the root system. With a large root system, the plant has a large surface area to extract the nutrients from the soil. So the plant can absorb much more nutrition in the flowering phase. This will result in large and sturdy buds.

What to look out for in the vegetative phase


At Sirius we assume an organic cultivation. The culture medium that is advised is potting soil. Keep the soil well aerated so that much oxygen can reach the roots. You can do this by mixing coconut, perlite and basalt flour through the soil. Do not give too much water during the growing period. If the soil is too wet the roots become lazy, because there is plenty of water. A soil that is too wet also increases the risk of fungi and root rot. If you keep the soil slightly on the dry side, you stimulate the roots to look for water. This will result in stronger root growth.


When growing indoors make sure that there is sufficient ventilation, so that fresh air is constantly present in the grow room or grow tent. Place a fan in the room. Not only to obtain air circulation but also to make the plant stronger. Mimic a nice breeze with the fan. The movement of the wind will make the stem stronger and thicker. Outside, it is more often a battle against the wind. Place bamboo sticks in the ground around the plant to restrict movement.


The sun is the best and most economical grow light available. Unfortunately, we can only use it for a few months to grow cannabis with. A bright sun with 25 degrees and a little wind is of course ideal. But even on cloudy days cannabis will grow well in the months with the longest hours of sun. Do you want to bring the sun inside? Make sure you use a lamp that is suitable for the growth phase. There are lamps that are specifically designed for the growth or flowering phase. A full-spectrum lamp can be used for both phases. When growing indoors, avoid growing the plant too high so that you can always maintain the right distance from the lamp. A cannabis plant will continue to grow in height into the flowering phase.


Choose nutrition that is appropriate for the growth phase. The nutritional needs of cannabis in the growth phase are different from those in the flowering phase. Calcium, magnesium, potassium and nitrogen are nutrients that contribute to a better growth phase. You can add these substances to the feed water. But you can also, for example, mix bone meal, bat manure and eggshells in advance with the growing soil. If you use mineral nutrients, do not use too much. Even if you stick to the recommended amount, there is a chance that the water in the soil will evaporate and the nutrient will crystallize. This will clog up the root mouths at the end of the root hairs and hinder their ability to absorb nutrients.

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