With ever more specialized and advanced growing systems for cannabis on the market, simple pots are still the most popular choice among most growers. They are especially recommended for hobbyist growers, those on tight budgets and with limited space.
Cannabis plant outdoors, under the full tropical sun, easily reach 3 meters in height. Though they will do perfectly well under artificial lighting and - if you want them to - grow as low as 50 cm, they will always be those plants that grow 3 m in the wild. One has to keep that in mind while choosing pots. While by using smaller pots you can put more plants per square meter, it will not necessarily improve your marijuana crop. With 20x20cm pots you will indeed put more then 50% more plants than with 25x25cm ones, but they will grow smaller and weaker if they don't get enough space for their roots.
For maximal utilization of the space in your grow area, square pots offer the greatest amount of room for the roots to develop. An alternative to the traditional square pot is an air pot - a cylindrical pot with multiple holes throughout its whole body. Such construction allows the root zone to get more air, reportedly increasing the final yield by up to 10%.