Pull off any oregano leaves that look insect eaten, black, wilted or otherwise unsavory and throw them away.
Rinse the oregano stems you have picked and pat them dry with a paper towel.
Pull the oregano leaves off of the stems.
Cover a cookie sheet with parchment paper. If you put the oregano leaves directly onto the metal tray, it will darken the herb as it dries it.
Spread the oregano out evenly over the cookie sheet.
Turn the oven onto the lowest heat setting possible.
Place the tray onto the top rack in the oven.
Leave the oregano to dry for two hours. Then pull out a piece of dried oregano. If it is dry enough to crumble easily, then it is ready to come out of the oven. If it is still too moist, check every 30 minutes until it is dry.
Place the dried oregano into an air-tight glass jar. Store it in a cool place out of direct sunlight.