NEW YORK • When Ms Summer Rayne Oakes' roommate moved out of their apartment in Brooklyn, she was left with more than just a vacant bedroom.

"All of a sudden, the apartment felt so cold and empty," said Ms Oakes, 33. "I needed to find a way to make the space feel warm and full of life again."

Her solution? A fiddle leaf fig tree - the first of nearly 700 houseplants that Ms Oakes, founder of Homestead Brooklyn, would eventually buy for her 1,200 sq ft apartment.

Her indoor forest spanning 400 plant species features everything from a sub-irrigated living wall in her bedroom, which is a wall of greenery that is essentially a self-watering planter with a built-in reservoir; a vertical garden made out of mason jars mounted to the living-room wall with wooden boards and hose clamps; and a closet-turned-kitchen grow garden with edible plants (ranging from greens to curry leaves).

"I didn't set out to build a jungle," she said. "I just saw how much energy and life the plants brought to the space and kept going."

It is a sentiment that more and more young people seem to be echoing in their own apartments. Wellness-minded millennials, especially ones in large urban environments that lack natural greenery, are opting to fill their voids - both decorative and emotional - with houseplants.

"Millennials were responsible for 31 per cent of houseplant sales in 2016," said Mr Ian Baldwin, a business adviser for the gardening industry. The 2016 National Gardening survey found that of the six million Americans who took up gardening that year, five million were aged 18 to 34.

"This group has more college debt and, as a result, are renting homes instead of buying," he said. "Houseplants are a low-cost way to have a green space at home."

Meanwhile, Greenery NYC, a botanic design company, has increased its clientele by 6,500 per cent since it was founded in 2010. Developers are finding ways to include gardens as an amenity for residents and more people - like Ms Oakes - are turning what little spare space they have in their apartments into indoor gardens.

"Our sales have doubled each year," said Ms Rebecca Bullene, founder of Greenery NYC. "And I attribute that mostly to businesses that want to attract millennial talent and millennials themselves who want more nature in their lives."

Inside her 1,800 sq ft apartment in Brooklyn, Ms Bullene, 37, cares for more than 100 plants. She has installed a green divider wall - a 1.8m by 1.8m steel shelving unit filled with a dozen wooden planter boxes and more than 50 plants - that separates her living room from her in-home office, as well as a terrarium and several other large-scale plants, including a 3.3m Ficus Audrey tree, to help break up the open layout of the space.

But for Ms Bullene, the plants do more than help define the apartment. They make her home healthier too. "Plants boost serotonin levels and dissolve volatile airborne chemicals. They actually make healthier spaces for humans to inhabit."

She cited a 2010 study from Washington State University that breaks down the benefits of indoor plants, including cleaner air and lowered stress levels.

Along with her floor-to-ceiling plant divider wall in the living room, she also employed a combination of plants that release oxygen at night in her bedroom - including aloe vera and sansevieria - so that she and her husband can breathe cleaner air while they sleep.

Millennial-minded companies are also going to great lengths to integrate greenery into their offices.

The Etsy headquarters in Brooklyn, for example, could easily be mistaken for an indoor botanical garden. Spanning nine floors and more than 200,000 sq ft, the office is home to more than 11,000 plants, including dozens of large-scale plant displays and living walls installed and maintained by Bullene and Greenery NYC.

"Every employee has a sight line to greenery," said Ms Hilary Young, Etsy's sustainability manager, who helps the company seek ways to conserve the environment. "It's a beautiful space that inspires and boosts productivity."

With the increasing number of young people searching for access to greenery in their residences, real estate developers have also jumped on the trend.

At the ARC in Long Island City - a new 428-unit "industrial-inspired" luxury rental building developed by the Lightstone Group - residents have access to a 1,100 sq ft glass greenhouse, where they are free to plant and grow their own vegetables and herbs.

But for those young urbanites who do not have the luxury of a communal garden or greenhouse, houseplants remain an affordable and renter-friendly option.

For instance, Ms Oakes has managed to make the bulk of her indoor garden self-regulating and, perhaps more impressively, removable.

Thanks to several do-it-yourself irrigation systems she hacked throughout her home, including two irrigation units she created using a 45m 1 hose that connects to pipes under her kitchen sink, she has to spend only about 30 minutes a day tending to her plants.

"New York City is tough," she said. "My plants gave me a sanctuary to come home to."

NYTIMES