Nature's first green is gold,
Her hardest hue to hold.
Her early leaf's a flower;
But only so an hour.
Then leaf subsides to leaf.
So Eden sank to grief,
So dawn goes down to day.
Flowers Blooming 
 
 
 In Spring, flowers, not just leaves, blossom on the branches of trees. Soon, though, these flowers disappear in the sweep of passing time. 

Nothing Gold Can Stay