Answer:
Okay, I dont know the poem you're talking about but I'll give this a go.
Yes, it is a metaphor, and it's obviously symbolic.
green here means Agriculture, plants, trees or generally speaking (Nature)
And gold would mean something that is precious,Valuable, not necessarily money but it might be money too.
The writer is insinuating that Nature is precious, Valuable.
The writer can also be saying that there is riches/money in Agriculture.
Now depending on the full context of the poem, you can pick either interpretation.
I hope I made it as simple as possible.