The bar itself was covered with succulents, and the tabletops with accoutrements like paintbrushes, plastic spoons and planters of potting soil. The crowd was here to learn the craft of terrarium building.

“Now, these succulents are very hard to kill, I promise,” said Lindsay Webber, the effervescent 28-year-old instructor of the class on terrariums. “You’ll only have to water them once every two weeks or so, and they only need a squirt or two of water.”

The two-hour lesson, called Plant Nite, was part of a program that started in Boston in 2015 and has spread to 32 states and Canada. It’s operated by a company called Paint Nite that capitalizes on the do-it-yourself movement and a clientele willing to pay for an experience — such as a primer on building terrariums.

These miniature landscapes are encapsulated in containers made of blown glass, ornate clay pots or a variety of other materials.

This Nov. 18, 2017 photo provided by Tracee Herbaugh shows a crowded hip hop bar in downtown Boston during Plant Nite where people where there to learn the craft of terrarium building. (Tracee Herbaugh via AP)

“I started getting into gardening a few years ago, and that’s when I saw these things (terrariums) getting popular,” said Diandra Escamilla, a 28-year-old Boston resident who attended Plant Nite. “I was seeing them everywhere, on social media — my friends started having them, so I started to get interested.”

Terrariums are hot. Many major retailers — not just gardening stores like Home Depot — are selling them. Some IKEA and West Elm stores, for instance, have offered build-your-own kits full of electric-colored rocks, tiny animal figurines, moss and popular succulents — hearty plants adapted to live with little light or watering. Likewise, terrariums have a devoted following on many social media websites, such as Pinterest, Twitter and Facebook, where plant-lovers exchange pictures, ideas and opinions of the miniature glass gardens.

The latest terrarium trend took off in the beginning of the decade, according to Maria Colletti, author of “Terrariums — Gardens Under Glass: Designing, Creating, and Planting Modern Indoor Gardens” (Cool Springs Press, 2015).

“Everyone thought it would be a phase and even drizzle away,” Colletti said.

That wasn’t the case.

Colletti, who teaches classes on terrarium building through the New York Botanical Garden’s adult education department, said terrariums’ portability and low maintenance makes them greenery mainstays that are here for the long haul.

“What could be better for an office or home to have a bit of nature where we view our miniature green world every day of our lives?” she said. “As our electronic digital world’s requirements increase, terrariums remind us of the larger wonder of the planet we live on, Earth.”

Terrariums date back at least to the early 19th century.

They enjoyed a pop-culture moment in the 1970s, said Megan George, author of “Modern Terrarium Studio: Design and Build Custom Landscapes with Succulents, Air Plants and More” (Fons and Porter, 2015).

George and her mother own a Durham, North Carolina, plant shop called Zen Succulent, where customers can partake in a DIY terrarium bar. Today’s terrariums are different, she said.

“The terrariums in the 1970s were in large globes that sat on the floor — they might have a large base to it,” George said. “People are living in smaller spaces now and they want something that fits on the tabletop; something that also functions as decor.”

For Swetha Ramachandran, 28, of Boston, who attended Plant Nite, a terrarium’s appeal is simple.

“They’re cute,” she said, matter-of-factly. “And I like the containers they come in.”