Cut mature parsley leaves by cutting at the base of the stalk of each stem. Cut the stalk as low to the ground as possible to encourage new growth. Harvest the outside leaves first, unless you are harvesting the entire plant.
Wash the leaves and pat dry with a clean paper towel. Cut off large tough stems, leaving the leaves and small stems that are easily crumbled when dry.
Spread the parsley leaves in a single layer on a cookie sheet.
Heat a conventional oven to 250 degrees F. Turn off the oven when the temperature is obtained.
Place the cookie sheet with the parsley arranged in a single layer inside the warm oven. Keep the door closed. The parsley should dehydrate as the oven cools.
Store dried parsley in an airtight plastic or glass container for up to one year. The color of the dried parsley is less likely to fade if it is stored in a dark location at room temperature.