Personal Greenhouse

Personal Greenhouse is an upgrade that costs 16 coins and has no prerequisites.

It is an upgrade that places a stone cube inside the castle that allows melons to spawn inside, containing a furnace inside. This upgrade also has the hidden stat of ever so slightly increasing melon generation inside the greenhouse specifically, having a 33% chance to add an extra melon every 2 seconds (Average of 1 per 6 seconds). It has a unique property of being able to change despite not being path related, as it changes if you go the Science path.

Trivia
This was the first upgrade ever added to the game.