"They will be like big fat walls of glass," Spear says, adding that the structures will be at least 3 metres long and 2.4 metres high.

"And when you look across the room, you are doing so through a haze of natural objects, filled with crystals, shells, fossils, orchids, turtles. It can be anything the buyer wants."

Spear's project - the 10,000 square feet villas will be finished in about 18 months - indicates an intriguing trend happening in the field of design, where more and more designers are looking at ways to bring elements of the outdoors inside. This goes far beyond sticking a potted plant in a corner. Instead, it is about imaginatively recreating indoors that sense of relaxation that comes from being in nature.

Julia Wong, a Los Angeles-based designer who has worked in Hong Kong, London and Tokyo, says that her approach is to "design the house from inside out rather than the other way around", and that her new favourite tactic is to create indoor cabana-style areas.

"I'm doing a house now where we converted a gym into a conservatory cabana, and we are putting the fireplace outside," Wong says.

"I think this is going to be the future of design, where there is more connection between the indoors and outdoors, without sacrificing technology." (To that end, the indoor cabana will have remote-controlled curtains.)

Plants like fukien tea and juniperus are often at the heart of elaborate indoor water gardens created by Plantaria, a New Jersey-based company that has been building traditional outdoor gardens for three decades, and a few years ago began "miniaturising" those gardens and bringing them indoors.

"We started thinking about people living in cities who don't have access to the outdoors," says Stephen Dekker, a co-founder of Plantaria.

"We decided to tackle that challenge. It's one thing to grow plants indoors. It's another to add water features. It adds a certain level of complexity."

The company has installed these water gardens in private residences all over the United States. They are typically about 150cm tall and 180cm wide.

Around a selection of evergreens and ground covers, Dekker creates a water reservoir with a small pump and subdued lighting. The result is a verdant green "indoor forest" with the sound of water trickling in the background. They are not cheap to install: at Plantaria, these live installations start at US$30,000.

"We are coming across more and more clients who want to enjoy the beauty of the outdoors inside, and also to be able to do it year-round," says Dekker, who runs the business with his father.

"We think there is a huge market for this in cities where people don't have access to the outdoors but want to enjoy the benefits of gardening, for example. Even though these are miniature gardens, they offer the fun and challenge of a real garden. You have to weed it, water it - there is maintenance involved, and it does give you a sense of nature."

"Because of the addition of the foliage, it basically becomes a live chandelier," he says.

For another client's home, he is also building a "live wall" - covering an entire wall with moss, succulents and blooming plants.

"We ruined a couple of trees," Goldstein says. "But I loved the idea of a wall in a home covered with plants, hanging loose, that just need to be sprayed with water every two weeks."

He is also working on "live windows", where he creates a slender space between two panes of glass, and places low-maintenance, soil-free air plants in the gap.

"Everybody needs and wants more live greens in their home," he says. "More than just putting a plant on a table."