What poem is referenced in Chapters 5 and 6 of The Outsiders?

Robert Frost’s “Nothing Gold Can Stay” is referenced by Ponyboy and Johnny.

Johnny is thrilled with the sunrise, and the boys’ reflection of the sunrise prompts Pony to quote from a Robert Frost poem about how things in nature do not last.  Pony is a good student and a lover of literature.  It makes sense that he would reference a meaningful poem at this time.

"The mist was what was pretty," Johnny said. "All gold and silver."

"Uhmmmm," I said, trying to blow a smoke ring.

"Too bad it couldn't stay like that all the time."

"Nothing gold can stay." I was remembering a poem I'd read once. (Ch. 5)

To Ponyboy, the poem is a reminiscence on nature and the fleeting nature of good things.  To Johnny, it is a reminder that in youth we are innocent, and then we are jaded by life.  Johnny is really touched by the poem.  He remembers it later when he is dying in the hospital.  Johnny gives Pony advice.

"Stay gold, Ponyboy. Stay gold..." The pillow seemed to sink a little, and Johnny died.

You read about people looking peacefully asleep when they're dead, but they don't. Johnny just looked dead. Like a candle with the flame gone. I tried to say something, but I couldn't make a sound. (Ch. 9)

Johnny was unexpectedly deep.  He did not do well in school, and his teachers did not really know how smart he was.  Yet he loved Gone with the Wind and enjoyed Frost’s poem.  He believed that Pony had a chance to have a better life, and reminded him when he was dying.

The poem takes on a symbolic meaning.  Johnny is telling Pony that the greaser life is not for him.  He is intelligent and thoughtful.  He has a chance to get out, and make something of himself.  Johnny did not get that chance.