An old-timer might plant potatoes in accordance with the phases of the moon. To best suit his cannabis plants, 31-year-old Sean Trombly carefully times his LED grow lights. This winter, Trombly is growing hydroponically, which for him means that his product blooms out of a mixture of finely ground coconut husks, fed with nutrient-enriched water in his garage rather than from soil.

When the plants are young, he’ll set his lights to 12 hours on, 12 hours off, in order to “flip” the budding plant “into flower,” he said. Once that happens, it’s roughly eight to nine weeks until Trombly is ready to harvest.

He works against the backdrop of a complex tangle of water pipes and the persistent drone of dehumidifiers. When it comes time to turn the light up to full throttle, it’s so bright Trombly has to leave the room.

“That’s when we’re really cooking,” he said. Off a Chelsea back road, rocket science has gone to pot. Trombly has grown cannabis at increasing levels of sophistication for a decade. He started in the black market before any form of legalization. Like the other growers that gave Vermont its reputation for some of the best illicit pot in the Northeast, Trombly could have found himself answering to criminal charges for growing even just a few plants.