On a recent weekend at Boston Gardener, a Dudley Square gardening supply shop, five people paid $100 each for a one-hour class in hydroponic growing. Store owner Jonathan Napoli’s tutorial was comprehensive, and his approach direct: Here is how to grow your own marijuana, at home and with maximum potency.

“Even if you’re a legal grower, you may want to be discreet about it,” advised Napoli, while attendees took notes on soil mixture, plant cloning, lighting options, and growth cycles.