Herbs should be harvested when the oils responsible for flavor and aroma are at their peak. Proper timing depends on the plant part you are harvesting and the intended use. Herbs grown for their foliage should be harvested before they flower. While chives are quite attractive in bloom, flowering can cause the foliage to develop an off-flavor. Harvest herbs grown for seeds as the seed pods change in color from green to brown to gray but before they shatter (open). Collect herb flowers, such as borage and chamomile, just before full flower. Harvest herb roots, such as bloodroot, chicory, ginseng, and goldenseal, in the fall after the foliage fades. Some general guidelines to use include:
- Begin harvesting the herb when the plant has enough foliage to maintain growth. Up to 75% of the current season's growth can be harvested at one time.
- Harvest early in the morning, after the dew dries, but before the heat of the day.
- Harvest herbs before flowering, otherwise, leaf production declines.
- Herb flowers have their most intense oil concentration and flavor when harvested after flower buds appear but before they open.
- Herb flowers harvested to dry for craft purposes should be picked just before they are fully open.
- Annual herbs can be harvested until frost.
- Perennial herbs can be clipped until late August. Stop harvesting about one month before the frost date. Late pruning could encourage tender growth that cannot harden-off before winter.
- Harvest tarragon or lavender flowers in early summer and then shear the plants to half their height to encourage a second flowering period in the fall.
Herbs acquire their fragrance and flavor from oils that evaporate into the air when the leaves are crushed. Ideally, you should use fresh herbs for cooking, but it is possible to retain some quality for later use. There are several methods to preserve herbs.
Freezing is one of the easiest methods to preserve herbs. Rinse the herbs quickly in cold water, shake off the excess, then chop coarsely. Place generous pinches of herbs in water-filled ice cube trays and freeze. Transfer herb-cubes to plastic bags or air tight plastic containers. Another method for freezing is to spread the herbs loosely onto a cookie sheet to freeze, then transfer the herbs into a large plastic bag and seal. When they thaw, herbs will not be suitable for garnish, but can be used in cooking. Do not re-freeze herbs after thawing.
Drying is the traditional method of herb preservation. If the herbs are clean, do not wet them. Otherwise, rinse dust and dirt from the foliage, shake off the excess water, and spread the herbs out to dry on paper towels or dishcloths until all surface moisture has evaporated. Remove any dead or damaged foliage. Then, tie the stems into small bundles with twine or string and hang them upside down in a warm, dry, airy place out of the sun. Be sure to make small, loose bundles and allow for good air circulation around each bunch.
UV rays from the sun and moisture from dew and frost can discolor and severely reduce the quality of many herbs. Thus, it is best to dry herbs indoors in a large empty closet, attic, or unused corner of a room. Drying herbs look quite attractive drying in a kitchen or pantry. If none of these places are practical, herbs can be dried in a barn, shed, or (least desirable) under the cover of a porch. Sage, thyme, summer savory, dill, and parsley are easy to dry. Basil, tarragon, and mints may mold and discolor if not dried quickly.
An alternative to hanging herbs to dry in bunches is to spread the herbs out on window screens. Suspend the screens over sawhorses or the backs of chairs. Turn the leaves often to ensure even drying.
To air dry herbs with seeds, tie the herbs in small bundles and suspend inside a paper bag with holes punched in the sides. Suspend the bag in a dark area with good air circulation. Collect the seeds when they are dry, and store in rigid light-proof containers.
Microwave drying is a quick and easy method to dry small amounts of herbs. Lay a single layer of clean, dry leaves between dry paper towels and place them in the microwave for 1 to 2 minutes on high power. Drying will vary with the moisture content of the herb and the wattage of the microwave oven. Let the leaves cool. If they are not brittle, reheat for 30 seconds and retest. Repeat as needed. Thick leaved herbs may need to be air dried for several days before microwaving.
Conventional ovens can also be used to dry herbs. Spread the herbs on cookie sheets and dry at the lowest temperature setting possible. Home food dehydrators also do an excellent job of drying herbs. Follow the directions provided with the dehydrator.
Herbs are sufficiently dry when they are brittle and crumble easily. When the leaves are dry, separate them from their stems and package the leaves in rigid containers with tight fitting lids. Glass or hard plastic are best, although heavy-duty zip-lock plastic bags can be used. To preserve full flavor, avoid crushing the leaves until you are ready to use them. Store dried herbs in a cool, dry place away from sunlight, moisture, and heat. Many herbs can be keep for a year if stored properly.