“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.
I also learned a new use of the word stack: a stack of money, usually a thousand dollars, though someone else said he worked for a guy who called $2K a stack.
These days, no one says “per pound” when quoting a price. It’s just “19” or “21” (i.e. $1900/lb or $2100/lb). If you say something about “19” or “21” or whatever, everyone will know you’re talking about the price for a pound of weed.
While I’m here this evening, here’s a bonus bit of lingo: P (pronounced “pee”). A pound of weed. When I first got here in ’95, people called them elbows, derived from of the abbreviation “lb.” I haven’t heard that in years, though.
Using all this in context, it might go like this:
Buyer: You got any Ps you want to move?
Grower: Yeah, four. How much you paying?
Buyer: Four Ps for two each…that’s eight stacks.”
(Translated: Four pounds of weed at $2,000 per pound will cost $8,000 and will likely be paid in eight pre-counted $1,000 stacks of cash.)
There, that’s just enough information for you to come here and try to buy weed while sounding like a dorky undercover cop.