“My plants are starting to stack” or “my plants are stacking,” refers to the marijuana plants switching from vegetative growth into flowering phase as the days shorten. In vegetative growth, the leaves are huge and the internodes (the length of stalk between leaf nodes) are long. As the plants prepare to flower, leaf production slows and internode distance shortens, so the nodes where flowers emerge from are said to “stack up,” ultimately becoming the dense masses known as colas.
Funny that I’d never heard this term until recently. It refers to the practice of mixing multiple strains of marijuana into the same bag. This was how it was often done in the past, where “pot was pot” and no one really cared so long as it looked and smelled good and got you stoned. Keep reading about why this practice is a relic