Super-Light Rooftop Gardens

On top of Linda Tool & Die Corporation, designed by The Gaia Institute, Red Hook, Brooklyn.

One of the major problems with creating a rooftop garden is the sheer weight of soil. While a typical rooftop is designed to handle about 20 to 40 pounds per square foot, some soil can weight up to 120 pounds per square foot. That means that, while you may have the space for a rooftop garden, it still might not be feasible.

But Gaia Soil, a social venture of Gaia Institute, a non-profit corporation, has found a way around that particular problem, using an unexpected product: Styrofoam. Environmentalists have long decried the use of Styrofoam, or polystyrene, because of its non-sustainability, health concerns, hazardous waste, and polluting qualities. It’s an unlikely coupling, to be sure, but it’s also quite innovative.

Gaia Soil uses recycled Styrofoam and pectin to create a synthetic soil. The nearly weightless Styrofoam is coated with pectin, which is a gel that “holds every plant and every fruit and leaf together,” according to Paul Mankiewicz, creator of the new soil. A cubic foot of Styrofoam and pectin weighs just 10 pounds and can hold up to 20 pounds of water. That’s a big difference from the 120-pound natural product.

Some are concerned about the possible risks associated with using Styrofoam as soil. They worry it might leech dangerous chemicals into plants, blow off into the air, or create other environmental concerns. But so far, there is no indication of any of those problems. It’s been in use for years in some locations and there have been no problems. The soil is also held down by a coconut fiber or burlap cover, topped with an inch or so of compost, and tied together with a root matrix—so there’s no real danger of it blowing off.

One of the best things about this synthetic soil—besides the fact that it makes rooftop gardening far more feasible—is that it’s completely sustainable. It uses materials that have already been made and would otherwise go into our waste system. That makes it completely carbon-neutral.