Seeds germinated, seeds planted, seedlings above the ground ... Now it's time for the KEY-GROWING PHASE! This means that from now on your cannabis plants will only grow, grow and grow! The reason for this is the light schedule (18 hours of light on/six hours off), as long as there is more than 12 hours of light per day available then there will be nothing but vegetative growth.
In this vegetative phase you can shape the plant (think Bonsai trees) just the way you like it, by applying techniques such as 'pruning', 'LST' (Low Stress Training), 'FIM' (Fuck I Missed), and 'Super Cropping'. These are all ways to prune your cannabis plant, so the plant will only grow in width instead of height (desirable with the SCROG method 'Screen of Green', and SOG method, 'Sea of Green' because this will keep the plant shorter. With the 'Lollipopping' technique you can also remove all the excess leaves under the plant, so no underdeveloped top forming will occur (saves a lot of trim work). I usually do this myself before/during the 3rd week of the blooming process (more about this in our next newsletter, where the focus will lie on the flowering phase).
If you've begun with seeds in a propagation medium such as coco, rock wool, turf or sponge pots then it should have been ready to be replanted to the next medium (full soil or bigger pot). The seedlings are very vulnerable at this stage, so it is important to minimize the shock as a result of replanting. When the replanting is not done in time then the seedling could possibly get 'root bound' (when there is no more room in the medium for the development of new roots). Other consequences of late replanting are dehydration and shortages. If the leaves of the seedling start to turn yellow it means that nutrients are needed that are no longer present in the medium, replanting and feeding is essential at that point.
Of course there's a big difference between indoor cultivation and outdoor cultivation. The advantage of indoor cultivation is that you can exactly determine how long you want to keep the plants in the growing phase before you put them in the blooming phase. You have full control over the growth and flowering stage with indoor cultivation because you can decide yourself when the lights go on and off. 18 hours of light and 6 hours of darkness is the most common light schedule in the growing phase, but this is just a general rule. Of course you can try to mimic nature even more precise, then you'd have to increase and decrease the amount of light gradually (because in nature the sun also doesn't go on and off suddenly).
With outdoor cultivation the weather (read: the sun) guides the entire growing/blooming process in cannabis plants.* After winter the days become gradually longer, this means more light hours per day and as a result a stimulus for cannabis plants to keep growing. When the summer has come an end, the days will become shorter again. This means gradually less light hours and thus a stimulus for the plants to switch over to the blooming phase. The growing/blooming process stems from the survival mechanism of the cannabis plant: reproduce before dying. Flowers (in female plants) and balls (in male plants) are required for the fertilization, and fertilization ensures seeds (progeny), so whole cycle can take place again and again.
* With outdoor cultivation in greenhouses the sun is the source of light and determines the amount of light hours. But even with greenhouse cultivation you can also artificially create a dark period, for example by darkening the greenhouse.
When the days become shorter then the plant determines when it's time to grow based on the amount of uninterrupted darkness. Cannabis plants measure the length of the dark period by means of the 'Phytochrome' hormone. This particular hormone has two stages, an inactive form (Pfr), and an active form (Pr). As long as cannabis plants get (sun) light then Phytochrome will remain inactive. However, when the plant is in the darkness for more than two hours then the hormone will change from the inactive form to the active form. And when the hormone level of the active form stays high for a long period of time (for a few days) then the vegetative phase will stop and the blooming phase will begin.
The Vegetative Phase
Humidity (Relative Humidity, RH) influences cannabis plants throughout their entire life cycle. Now that your plants are in their main growing phase the humidity level may be adjusted a bit more. At this stage the RH may fluctuate between 50% and 80%, this is possible because your plants now have a much larger (leaf) surface to transpire. If the humidity level goes down then your plants are more likely to transpire, but this causes less stress compared to the seedling phase (that's why the RH needs to be more than 70% in the seedling phase). Pay attention to the watering in the vegetative phase, because now that your plants are able to transpire more quickly (when the humidity level goes down), they will also absorb more feeding water from the medium, and when there's insufficient watering it could lead to dehydration of the plants.
The vegetative phase (veg) is often misleading for new growers since cannabis plants do not require 24 hours of continuous light to remain in veg. The fact is that plants also need a dark period in order to 'rest', just like people. So if you keep your plants under 24 hours of light, you make them perform extremely hard without any rest. And as everyone knows, you need to rest after you have performed well, so this is also the case regarding your beloved plants. According to Nico Escondido, the Cultivation Editor of High Times, there is another important reason why your plants need a dark period. During the dark hours the growth and development of roots occur, which is essential for the development of young plants as you know. The roots ´breathe´oxygen, (in contrast to the rest of the plant, where carbon dioxide is absorbed), and the breathing of oxygen by the roots mainly occurs during the dark hours. For these reasons it is strongly recommended to give your plants a few hours in the darkness during the vegetative phase.