Once your plants have sprouted, they enter what we call the vegetative stage, where hopefully they will become big and strong before you change them to the flowering stage in a few weeks time.
This vegetative stage will last on average 4-6 weeks indoors for most people simply because we only want the plants to reach a certain maximum height. (Most cannabis plants, once moved into the flowering stage will almost treble in height) In general, the longer you wait, the taller the plant will become which in turn will produce a higher yield but there is certainly a point of diminished returns at which waiting any longer can actually reduce yield because the lights can only penetrate so deep into the plants but for the typical grower 4-6 weeks is usually perfect.
Throughout this veg stage, you should be using lights that are sufficient in the blue spectrum range. Look for daylight bulbs and if the package displays colour temperature, you want 6,500K. Nowadays there are HPS bulbs that have dual spectrum, meaning they are able to provide the right type of light during both stages of growth. This is what we use ourselves nowadays.
These lights should typically be on for 18 hours and off for 6 hours, which is achieved with the help of a decent timer, tho it is certainly possible to veg with 20 hours or even 24 hours of continual light. Pick a sunrise/lights on time and try to keep this the same throughout the entire plant’s life. We will only ever be adjusting the sunset/lights off time.
Try to keep the plants in complete darkness when the lights are off as light leaks can increase the chances of hermaphrodites (having both male and female parts). Particularly if you are not using top quality seeds.
If you are only using CFL’s or fluorescent tubes, you should place the lights within a couple inches of the tops of the cannabis plants. They can be practically touching the plants as these lights do not produce much heat at all but 2-3 inches or so away is ideal. If your lights are too far away, it might cause your plants to stretch for the light and stretching is usually detrimental to the growth, giving weak stems. For the best yield you want thick, strong plants, not tall lanky ones.
Keep a thermometer in the room and monitor the temperature. While the lights are on, the temperature should be between 70-80 degrees Fahrenheit. We aim to grow our plants at 78F which in our own environment we find perfect. During darkness, the temperature will obviously drop but we don’t want it too cold, ideally this drop will be less than 15 degrees (F).
A humidity metre is also important. Try to keep the humidity between 40-60%.
As your cannabis plants get bigger they will begin branching off into several leaf branches. You may begin to notice signs of sex showing up at the nodes, but in general you will not be able to sex your plants until you move to the next stage.
If you used a good quality soil with nutrients already included, (do not use time release soils) you should not need to add any nutrients for the first couple of weeks. A lot of new growers over fertilise and this can end up damaging the plant. Be careful if you are using nutrients and follow the directions that come with the product. We will usually give the first feed at half the recommended dosage so that we can see how they react to this feed.
Your primary aims at this stage are to water them and provide them with light. Do not over water them (see watering cannabis plants)
Once your cannabis plant is about a third to half as tall as you would like it to be, preferably with 4-6 nodes, you can begin the flowering stage That’s probably about 4 weeks to get the best combination of factors.(the typical indoor grower)
I like my girls mature and leafy before flowering. I like to keep the humidity levels up here in Spain for good leaves, i.e around 50-60%