Fresh herb leaves can be picked whenever the need arises, but leave enough foliage on the plant to maintain its health.
Stop harvesting leaves from your perennial herbs in late summer to allow the plant to store enough food to get through the winter months.
If you intend to save seed, allow the plants to flower and set seed, then harvest the seeds when they change color from green to brown or gray, and allow them to dry thoroughly before storing.
If you intend to dry the herbs, pick them just before the flowers open; at this time the leaves contain the highest content of aromatic oils. Cut individual stems about 6 inches below the flower buds, remove dead or damaged leaves, rinse gently in cold water, dry them with paper towels. Tie the cut stems in small bunches and hang the bunches in a well-ventilated, low-dust darkened room. Label each bunch so they don’t get mixed up – many dried herbs are similar in appearance.
Individual leaves can also be dried in a single layer on trays or screened racks. Stir the leaves gently daily to speed the drying process. Be sure and label the trays.
When the herbs are dry, remove leaves from stem or from trays and place into sealed glass jars. Check the jars in about a week to see if there is any condensation in the jars, indicating that the leaves were not completely dry. If so, remove the leaves from the jars and spread out to complete the drying process. Dried leaves can be ground or crushed for use.
Some herbs, basil for example, lose flavor when dried and are better preserved by freezing. Finely chop fresh leaves, pack into small containers such as ice cube trays, cover with water and freeze. The ‘herb cube’ can then be added to the dish during the cooking process.