SAN FRANCISCO (CBS SF) — When the expanded San Francisco Museum of Modern Art reopens to the public in May 2016, it will be the largest modern art museum in the United States, and one of the museum’s largest features is actually growing outside.

“To me, this is an art piece in itself,” says horticulturist David Brenner, who helped design the largest living wall in the Bay Area. The towering installation of plants dominates the courtyard on east side of the expanded museum. Brenner says most of those plants are California native, so looking at the wall is a little bit like wandering up the side of Mount Tamalpais.

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The wall is also a feat of green engineering. Brenner is working with what you might call flora on plastic, as the wall itself is actually recycled bottles, turned into massive sheets of felt. Pointing to the plants tucked neatly in small pockets, Brenner explains that the felt is “providing the water, the nutrients, and the growing medium that the roots are going to grow into.”

The wall is also water efficient. The plants, through the felt, are precisely hydrated using recycled water. There are also about ten different sensors in the wall to measure whether or not the plants are properly hydrated.

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The biggest challenge, however, was getting each of those plants in just the right place. That meant projecting a blueprint across several stories, drawing out the pattern, and carving out every single pocket. From there, it was planting by number, and individually planting some 19,440 plants.

With lots of hallways, hard surfaces and white walls, even a world-class museum can start to feel a bit stifling after a few hours, but stepping outside to the living wall the moment ends with a change of setting that museum visitors can actually feel.

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“I think you need a break at a point, to see something that really feels natural,” says Brenner, who credits the expansion’s architects with envisioning how a living wall could create a needed break for visitors. At nearly three times its original size, walking through the new SF MOMA could be an all-day affair, so a few moments of natural relief might be well deserved.