evergreen
A plant or thing that stays fresh and useful for years.
Evergreen describes trees and plants that keep their green leaves or needles all year long, even through cold winters. While maple and oak trees drop their leaves every fall and stand bare until spring, evergreens like pine, spruce, and fir trees stay green and full through every season. Their needles might eventually fall off and get replaced, but the tree never looks bare.
Beyond plants, evergreen describes anything that stays useful, interesting, or relevant year after year. An evergreen story is one that people keep reading long after it was written, like Charlotte's Web or The Lion, the Witch and the Wardrobe. An evergreen song is one that sounds just as good decades after it was recorded. Your grandmother's favorite song from when she was young might be an evergreen classic that you enjoy too.
In this sense, calling something evergreen is high praise. It means the thing has lasting value that doesn't depend on current trends or temporary interests. Just like an evergreen tree stays beautiful through all seasons, an evergreen idea, book, or piece of advice remains valuable through changing times.