Instructions
Log onto your Facebook account and click on "Backyard Monsters" from the list of games in the left column of the screen. The game will launch and the game map will appear.
Look at the borders of your particular area. Just outside the margins should be mushrooms, along with trees and shrubs.
Click on the mushroom you would like to harvest and your workers will stand at attention.
Click "Pick" when prompted and your workers will move to the mushroom and harvest it. You will then be given a reward of shiny.
Repeat the steps for any remaining mushrooms you would like to harvest. Once they are all harvested it will take 24 hours for them to regrow.