The Greenhouse is part of the Botanical Research Laboratory (called the "production zone" on the map). It is across the bridge to the right of Main Stret and the Hub. You can only reach it by lowering the Bridge with the Steam Battery and the key from Captain Ziggs' quarters, at the top of the Hub.
its in the museum on mainstreet of steamworks island :)
There is a very old Dirty Beaker in the Steamworks Museum (far upper right). Use the machines and climb the vines to reach the beaker. You need this at the Greenhouse in the Laboratory (Production zone, right side of the island).
It's Steamworks Island #14th Island
(The solution is at the related question "How do you beat Steamworks Island")
the crab on steamworks island is next to the living quarters
You go to Steamworks and head to the museum and there is the Deogen
steamworks island
There is a video walkthrough at the related link below. There are written WikiAnswers solutions at the related questions, as there are for all Poptropica islands. (How do you beat Steamworks Island) (What is the walkthrough for Steamworks Island)
Steamworks island
you can get it on the far left of steamworks island, past the living headquarters.
how to do the bridge terminal on poptropica's steamworks island
jump