Instructions
Look on the grass in the wide-open spaces of your backyard. The mushrooms are red with white spots and white bases.
Search behind any tall or large buildings on your plot of land; mushrooms may be hidden behind them.
Click the green "-" button to zoom out as far as possible, then look for mushrooms on the borders of your plot.
Place a Yard Planner building in your backyard. This building gives you access to the planner's map, which is in 2-D and maps all the mushrooms in the area. Mouse over the dark gray squares labeled "Mushroom," then head to that area on the map.
Click a group of mushrooms and select "Pick" from the menu to harvest them.