"Instead of putting a palm or a ficus in a corner, it's something you can install on a wall, in a series of containers on a grid, essentially what is a living wall, " he said.

CNN: Terrariums make it big by going small

Mr. Hagel also outlined a series of upgrades under development, including plans to install a second advanced radar system in Japan to more quickly detect North Korean missile launches.

WSJ: U.S. to Boost Missile Defenses in Response to North Korea