It means that the Gantang trees in Guanzhong area have grown taller and people are remembering Zhao Bo, and the flowers are blooming all over the ground in Heyang and people are remembering Pan An.
This sentence comes from the second paragraph of Li Weng Duiyun, Shishi Han, a collection of essays written by Li Yu, a litterateur in the late Ming and early Qing dynasties.
Zhao Hu, people called him Zhao Bo. Legend has it that there was a Gantang tree in his residence. After he left, people protected the tree and wrote a poem called Gantang. Memorial.