Harvest basil leaves for winter storage in the morning once dew has dried but before the heat of the day arrives. For the most intense flavor, choose stems that have small buds that have not started to open.
Gather basil in small bundles of three to five stems. Tie the stems with garden twine or wrap with an elastic to hold the bundle together.
Hang the bundles of basil upside down in a dry, well-ventilated area to dry. Check the bundles daily and turn as necessary to allow all leaves to dry thoroughly. Drying time varies, depending on the size of the bundles, humidity level and temperature, but most dry within five to 10 days.
Remove the leaves from the stems once they are completely dry. Leaves and stems should be crisp and brittle. If portions of the leaves or stems are pliable, they require more drying time.
Place the dried basil leaves in a glass jar and seal tightly. Store in a dark, dry area free of moisture or humidity.