Tech companies have been eager to test ways to make workplaces more conducive to creativity. Some turn their offices into grown-up playgrounds, with beanbag chairs, ball pits and Ping-Pong tables.

Image Renderings of the spheres at Amazon that show what the interiors are expected to look like. When they open in early 2018, the spheres will be packed with a plant collection worthy of top-notch conservatories. Credit... NBBJ

The more refined alternative now catching on is to make nature the star of the show. Apple, for example, has hired an arborist, Dave Muffly, to oversee the planting of about 8,000 trees on its new 176-acre campus in Cupertino, Calif., which will surround a spaceship-shaped new building where Apple employees will work. The mostly native trees are intended to restore the natural landscape that once blanketed Silicon Valley.

What makes Amazon’s project unusual is its location — in the heart of a city, rather than on a sprawling suburban campus of the sort favored by most other big tech companies. Amazon, the largest private employer in Seattle, has more than 20,000 employees spread out in more than 30 buildings in the city. Its current construction plans will give it the space to more than double its local head count.

Mr. Bezos has said that Amazon is staying put in a city because the kinds of employees it wants are attracted to an urban environment. But the concrete and steel canyons around Amazon’s new downtown properties do not have a lot of greenery. That is where the spheres and Mr. Gagliardo, whom Amazon hired to fill them with plants, enter the picture.

Margaret O’Mara, an associate professor of history at the University of Washington, sees the spheres as a kind of Walden Pond under glass. “It’s a retreat, a cathedral away from the hubbub of the city,” she said.

There was plenty of noise inside the spheres on a recent tour, as workers welded steel, pounded bolts into place and sawed concrete inside the half-built structure. The glass panels that make up the carapace of the spheres were being lowered onto steel supports in eye-catching shapes.