Since the question is full sentence, I cannot write whole sentence answer in the Terget term space. So here you go.

"We set the Greenery Day aside for our employee to appreciate trees and plants, and have them nurture greeneries themselves."

This company is calling the day 「緑化の日, but its official name by the government is "みどりの日" as dosanko-san pointed out. I believe they are referring to the latter.

Please do not be so desperate to "jump off cliff".