What is Wemmick’s “green-house”? Why is this an odd metaphor? Why might Wemmick treat the prison this way?

Remember that Wemmick is the clerk for Mr. Jaggers, the lawyer. This can tell you why he would treat the prison as a greenhouse.

So the answer to the first question is that Newgate Prison is Wemmick's greenhouse.

This is an odd metaphor because a greenhouse is a place where things grow. You would not expect to use this metaphor for a prison. Maybe for a school, where kids learn and grow, but not a prison.

But Wemmick works for a lawyer. And he likes to get "portable property" from the criminals. So if you work for a guy who defends criminals, it makes sense to go to the prison and "cultivate" the prisoners so they will hire you again sometime when they need a lawyer.

Thanks Jill for the short answer

You are so helpful Jill