Wellness-minded millennials are filling their homes with clean-air houseplants, and real estate developers are realizing that a love for greenery can be used as an amenity to attract buyers.

Millennials are looking for spaces to add indoor gardens. Real estate developers are jumping on the trend. The ARC in Long Island City, a 428-unit luxury rental building, allows its residents to use a 1,100-square-foot glass greenhouse where they can plant and grow their own vegetables and herbs.

“It’s been a tremendous selling point to prospective tenants,” Scott Avram, senior vice president of development at Lightstone, told The New York Times.

The Margo in Brooklyn features a living wall in the lobby and a rooftop garden with plots that tenants can use as their own gardens.

“Wellness is a priority for our millennial-aged residents,” says Dave Maundrell, executive vice president of new developments for Brooklyn and Queens at Citi Habitats. “They’re willing to pay more for access to a green space.”

Millennials are adding more houseplants inside their homes, too.

“Millennials were responsible for 31 percent of houseplant sales in 2016,” according to Ian Baldwin, a business adviser for the gardening industry. Of the 6 million Americans who started to garden in 2016,

5 million were ages 18 to 34, according to the 2016 National Gardening survey.

“Houseplants are a low-cost way to have a green space at home,” Baldwin says.

And it’s not just adding one or two houseplants, but they’re adding in hundreds to their home, featuring indoor gardens and divider walls of greenery.

Summer Rayne Oakes has filled her 1,200-square-foot apartment with nearly 700 houseplants. She has a subirrigated living wall in her bedroom, a vertical garden made out of Mason jars in the living room wall, and a closet transformed into a kitchen grow garden with edible plants, like herbs.

Rebecca Bullene, the founder of Greenery NYC, a botanic design company, has filled her 1,800-square-foot apartment with more than a hundred plants, including a six-foot-by-six-foot steel shelving unit filled with a dozen wooden planter boxes and more than 50 plants alone that separates her living room and her office. She also uses large plants, like an 11-foot-tall ficus audrey tree to help break up an open floor plan.

She’s drawn to the health boost from the plants, not just the look. “Plants boost serotonin levels and dissolve volatile airborne chemicals,” Bullene says. “They actually make healthier spaces for humans to inhabit.”

She also uses a combination of plants in her bedroom that are known to release oxygen and clean the air, including aloe vera and sansevieria.