NTT Urban Development Co. and NTT Facilities Inc. have found that growing sweet potatoes on roofs is an effective way to combat the high heat found in urban centers.

The two companies said tests of their farming technique have yielded impressive results at curbing high temperatures and they aim to implement it next summer.

At present, most people grow grass or small trees on their roofs to fight the heat island phenomenon, in which temperatures are higher in cities than in the surrounding countryside because of the concentration of asphalt and concrete.

Sweet potatoes have the advantage of growing fast, and the plants’ large and numerous leaves offer more shade. The thick blanket of leaves also allows 50 percent more water to evaporate compared with grass covering the same area, absorbing more heat in the process, the two companies said.

Recent trials have shown that when the temperature on a roof’s surface is 55, the surface temperature under the sweet potato leaves can be as low as 30, they said.

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