The growth or vegetative fase of your plant is the time it needs to get it’s height before he starts making flowers. This fase is important and decisive for the health and structure of your plant and the final end result. It is desired not to exhaust your plant at this stage but to save his strength to use later on as an extra energy boost during the flowering phase. In the nature outside this is normal for the plants. In spring at daytime the temperatures are pleasant but in the nights still cold. This will keep your plant short and will grow with short internodes with a lot off sidebranch. At a later stage this will give a nice dense top deck where you get your yield from. To focus on the main top is wrong ( unless it is a maintop dominant genetics). The weight is for 65% in the middledeck, the sidebranches and for 25% in your maintop and 10% in the lowerdeck. This is why the bit colder nights are crucial and will make sure your plant will not grow to fast and save his energy for the flowering stage. Also the humidity of your medium and the nutritional content will determin the shape and height of your plant. A little recap in how you can shape your plant.
To have a long plant with long internodes if you are afraid that your plant is too short:
Day temperature on 28 degrees
Night temperature on 22 degrees
Keep the medium moist for maximum pressure on the roots
Give Low EC for longer plants.
If you want a plant to stay short it is the opposite:
Day temperature on 24 degrees
Night temperature on 16 degrees
Keep the medium a bit dry for less root pressure
Keep EC high to avoid stretching
You can keep this up untill the First flowers are in them and there is practically no more growth. With indica strains this is untill the third week of bloom. With sativa strains is this untill the fifth week of bloom. With long-flowering strains this is even untill the eigth week of bloom, but we advise with this kind to choose the short keeping variant.