It may not be celebrated like roses or orchids, but marijuana is a flowering plant all the same, with a community of growers dedicated to its propagation (and boosting THC content). Each November, the best of them gather in Amsterdam for the High Times Cannabis Cup, a kind of taste-off for the stoner set.

“It’s a couple of hundred strains of the world’s best marijuana,” said Mark Haskell Smith, whose new book, “Heart of Dankness,” published by Broadway Books, delves into the subculture of high-end pot cultivation.

Mr. Smith visited hippie growers in California’s Sierra Nevada mountains, large-scale greenhouses in the Netherlands and medical marijuana dispensaries in Los Angeles. As someone who writes that he grew up smoking “Kansas dirt weed,” Mr. Smith finds today’s lab-refined strains, with names like Habañero Haze and Kosher Kush, to be a mind-bending botanical advancement. A Californian, Mr. Smith obtained a doctor’s recommendation to smoke pot legally under the state’s medical marijuana law, even testing out his green thumb. “I actually grew two plants in my driveway in these microfiber pots,” he said. “One got attacked by caterpillars, but the other turned out pretty good.”

He recently discussed more accomplished pot growers and parsed the difference between sativas and indicas.