Hedge
Fence
noun
A hedge (or fence) root is where the hedge and fence grow from. What grows from this? Well, it's simply a hedge or a fence.
The readings are the kun'yomi readings of the kanji. With 垣 that's the one you learned and with 根 that's the vocab version of the kanji.
男は垣根の上にそっと義手を置きました。
The man placed his prosthetic hand gently on the hedge.