A root-bound Cannabis plant in a container too small for it’s size will yield far less than a plant with enough room for the rhizosphere, or the zone of soil surrounding your roots. Taking the time and care to transplant weed plants properly will also cause less stress and keep them growing happily, so it’s well worth the effort. As the saying goes, “More Root, More Fruit!”, so give your roots plenty of room for a heavier harvest of buds.
I don’t recommend that you transplant weed plants during the flowering stage because it can take up to a week for the plant to recover from the shock. If you think you need to upgrade your plants’ containers, it’s ideal to do it during the vegetative stage, for best results. No matter how gently you transplant, it will take a few days to a week to recover from the shock and you can’t afford to lose this time during flowering while the plant is supposed to be using its energy to pack on colas. The only exception would be a heavily root-bound plant that needs to be transplanted during flowering but this is a mistake that could and should have been avoided with an earlier transplant.
The degree to which transplanting can hurt a plant depends on when the transplantation is done and how gently it is accomplished. First, prepare the new larger pot with some of your planting mix (I like square pots more than round ones because the same size can hold more soil). Then, water the plant in its original small pot thoroughly to ensure that the soil and root ball stay together without crumbling apart. Gently remove the plant from the original pot – I like to hold it by the trunk at the base and turn the entire pot upside down and tap it to loosen out the plant. Place it into the new pot and backfill the remaining mix around the outside. Water it in and fill any remaining gaps keeping in mind that the plant may droop for a few hours before bouncing back strong.