土 resembles dirt on the ground. 
（chuí）is a phonetic component and resembles flowers. Together, they symbolize stones and plants that were used in ancient times to delineate boundaries. The original meaning of 垂 was border area or frontier, a meaning that is now expressed by 陲.
Characters formed by the phonetic component 垂
錘/锤(chuí) 捶(chuí) 陲(chuí) 棰(chuí) 菙(chuí) 棰(chuí)
倕(zhuì) 娷(zhuì) 硾(zhuì)
崜(duǒ) 涶(tuò) 腄(hóu)
厜(zuī)
睡(shuì)