Vertical or horizontal? It used to be that making the choice between living up or out depended on several typical factors—price, location, amenities, convenience. But for many urban luxury homebuyers today, that decision also hinges on the amount of outdoor space, and, more specifically, the ability to deck that space out with container gardens.

This growing trend is not just something that urban homebuyers are tacking onto a long list of features they’d like in their new home; in some cases, it’s driving the sale.

“My last three last three high-end buyers all wanted a large terrace in their condo so they could have a big container garden,” says Rodolfo Zavala of Coldwell Banker Gold Coast. Two of those three buyers came from large homes in the suburbs; “One of them sold a huge mansion in Chicago’s North Shore. The ability to have a terrace that was substantially larger than a balcony where they could hire a designer and add container gardens and other features was a must have.”

While a container garden can fit on a small balcony, properties with larger terraces are in high demand, but not in large supply. You can buy this 50th floor penthouse in Chicago’s in-demand River North neighborhood that, in addition to the 7,000 square feet and 360-degree views of the city, provides 1,000 square feet of terrace space. Or perhaps you’d prefer this one-of-a-kind penthouse atop the Las Olas River House in Fort Lauderdale, where floor-to-ceiling glass looks out onto the large terrace space—and if you ever tire of the city, water, and container garden views, you can take a gander at the original Picasso, Basquiat and Warhol pieces that are part of the purchase price. On the west coast? Outdoor space is also at a premium in San Francisco, which is why the penthouse at 2100 Green — offering one of only a few rooftop private garden decks in Pacific Heights and some of the best views available on the ridge — is so highly coveted.

“Its oasis is the potted garden of assorted trees and shrubbery on the exclusive and private roof deck,” describes listing agent Dona Crowder of Coldwell Banker Residential Brokerage in San Francisco. “In a city where land is limited — only 7 x 7  square miles, in many upscale neighborhoods (or high-rise buildings), ornate container plantings and imaginative deck gardens are a way to soften the urban landscape.”

Not surprisingly, you’ll pay a premium for any of these exquisite homes.

“One of my clients had to spend $1 million more than their initial budget to get the terrace they wanted,” said Zavala. “It was very important to them.”

Zavala, owner of a South Loop condo with 700 square feet of terrace space that where he spends almost every night cooking and dining when the weather is nice, understands the draw.

“When you walk into a condo that has a large terrace with container gardens, you don’t expect it,” he says. “In the middle of this jungle of steel and glass, there’s this beautiful natural element. It’s a big selling point for buyers, and, as someone who has a container garden, it’s great to have, especially in Chicago, where we have long winters and people can’t wait to get outside as soon as they can.”

So what’s compelling this trend? An increasing variety of available plants, for one thing.

“Because of the popularity of container gardens, growers have responded by making a variety of plants more compact or offering them in dwarf varieties,” notes Janella Sykes, manager of Farmers Market Garden Center, an urban garden specialist in Chicago. “There’s a greater availability of edibles, which are huge right now. Blueberries and raspberries can be easily grown in a container now, instead of taking over your yard. The same is true of Heirloom tomatoes, which usually ramble and take up a lot of space, and vegetables like zucchini.”

Also popular are plants that provide serene garden spaces in colors and configurations that mimic the interiors of the home.

“I’m seeing more and more clean lines and more geometric design, mirroring interior design trends,” says Zavala, “with less color overall and monochromatic gardens. Some are all white or all green, using a variety of grasses, dwarf Japanese Maple trees, succulents, and very little flowers. Not only is it a design trend that’s contemporary and clean, but it’s also easier to maintain. If you plant extensive flowers in the spring, by summer you almost need to replant the entire terrace.”

The popularity of container gardens may largely be an outgrowth of space constraints, but that’s not stopping suburbanites from getting with the trend.

“They’ve really caught on everywhere,” says Sykes. “Containers eliminate a lot of the guesswork on soil, so they’re a great choice regardless of the type of home. They also make citrus trees, which are very popular but won’t sustain tough winters, possible, because you can just roll the container inside when the weather is cold.”