Herb leaves are harvested when the plant's stock of essential oils is at itshighest. Leafy herbs such as basil, savory, marjoram and chervil the peak time is just prior to blossoming. Harvesting should take place in the morning when the plants are free of dew. If possible, choose a day that will be hot and dry. Cut at least six inches of top growth below the flower bud and do not wash plant unless it is absolutely necessary for some essential oils are lost during the rinsing process, impairing flavor. If you must wash them to maintain cleanliness, rinse them under cold water, shake off excess water and hang the herbs in small bunches in the sun to dry. Do not leave in the sun beyond necessary drying time. Take the herbs in to continue the drying process placing them in a warm dry well-ventilated place free from strong light. Herbs are tied and hung leaves down, allowing the essential oils to flow to the leaves. To prevent dust from gathering on the leaves, tie a brown paper bag with many ventilation holes punched in it to aid in air circulation that is very important in the drying process. Gather the paper bag together at the stems and bind it with string or a rubber band. The bag also shades the herb from direct light that tends to darken the leaves. Sage, savory, oregano, basil, marjoram, mint, and lemon balm are best dried in this fashion.
The leaves from thyme, parsley, lemon verbena, and rosemary may be removed from the stems and dried in single layers on screened trays. Old window screens can be used for this purpose. For best results, drying time should not exceed three or four days. Weather conditions may not always be conducive for quick drying, therefore, if not entirely dry in two weeks, (crumble easily when crushed with fingers), place in 100 degree oven until you achieve the desired results. Store in air tight containers free from direct light.
Herb seeds, i.e., fennel, coriander, cumin, caraway, anise and dill to name a few, are harvested when the seed pods or heads have changed color but before they shatter. You can use either of the two drying methods outlined previously. If you use the screened trays, be sure the screen mesh is very fine, not to allow the dried seed to pass through. I personally use the paper bag.
Tip: Do not over dry. The herb must be free of moisture to prevent mold. If over-dried to the point of turning to dust when crumbled, all flavor may be lost. Store herb seed and leaves whole and crush right before use. I use a mortar and pestle for that purpose. Do not store herbs in paper or cardboard. Glass or tin is best and tinted glass if kept in an open area. Keep out of strong light and away from heat sources.