Herbs can be harvested throughout the growing season—and even throughout the dormant season, if grown indoors. The following tools are useful to have on hand at harvest time: pruning shears (remember that sharp shears are less likely to injure plants or you), rubber bands or twine (for tying bunches of stems together), and, on very hot days, a bucket of cool water to immerse herb stems in.
If you're harvesting seed heads, bring along small paper bags to contain them. To harvest roots, you'll need a garden trowel or hand fork.
When to Harvest
Small amounts of herbs can be harvested for immediate use throughout the growing season. Major harvests, however, should occur a few days before each plant flowers, when the concentration of essential oils in the leaves is highest. Flowering time varies among herbs, so observe your plants carefully. Perennials should not be pruned or harvested heavily during the last 30 to 45 days of your growing season, before your first seasonal frost is expected; this will ensure that your plants are strong enough to survive the dormant season. You can harvest annuals, such as basil, right up until they are killed by frost; after that, pull entire plants and compost them.
When harvesting a large amount of herbs for drying, making vinegars and potpourris, or other purposes, try to work during the cooler times of the day, when the herbs' essential oils are unlikely to evaporate and their foliage is less likely to wilt. The best time to harvest herbs is just after the morning dew has completely dried, because this moisture can cause the herbs to mold--making them useless for any kind of preparation.
It's important to remove herb leaves and stems in a way that will help promote new growth, rather than harming the plant. The method for doing that varies from herb to herb. Fortunately for the home gardener, most common herbs fall into just two of the more than 300 identified plant families, so it is relatively simple to learn the preferences of these two families.
Mint (Lamiaceae) Family
Herbs Included: basil, bee balm, hyssop, lavender, lemon balm, marjoram, mint, oregano and rosemary
Cut in the middle of their stems, just above a set of leaves, or pinch off the growing tips from the ends of the stems. Two new stems will form at these junctures, promoting abundant, bushy growth. Members of the mint family will produce vigorous new growth when cut back by one-third between the time they flower and set seeds, increasing their yield substantially. Tarragon and lemon verbena have growth habits similar to mint; harvest them the same way.
Parsley (Apiaceae) Family
Herbs Included: angelica, caraway, dill, fennel, parsley and sweet cicely
Harvest by cutting stems at their bases from around the outside of the plant. This will encourage new shoots to grow from the center. Annuals in the parsley group (such as cilantro) produce leaves for a brief time before they flower. Harvest these leaves three to six times during the period before flowering.
Other types of herbs can be harvested and pruned using methods suggested by their growth habits. Chives, for example, sprout a dense cluster of blades from their bulbs. Cut individual chive blades close to the ground, or cut the entire plant to 1 inch above the soil level. New blades will generate from the bulbs. Bay (Laurus nobilis) and scented geranium both sprout leaves along their stems. Harvest these leaves individually. For herbs that produce both usable leaves and flowers, such as yarrow, feverfew and tansy, wait to harvest the entire stem until just before the blooms open.
Gather seeds when they are ripe. On most plants (including caraway, coriander, dill and fennel), the seed color changes from green to tan to light brown as ripening occurs. To harvest seeds, pull up the whole plant from the soil when the seeds are barely ripe. Hang the plant upside down with a paper bag tied over the seed heads; as the seeds ripen and dry, they will drop into the bag.
Another way to collect mature seeds is to tie muslin bags over the seed heads of plants as they grow; the bags will catch seeds as they drop naturally. If the seeds haven't dried naturally on the plant, spread them out on paper towels and allow them to finish drying, Store dry, harvested seeds in a cool, dry place in cardboard boxes or in twists of aluminum foil.
Herb flowers, such as those of calendula, lavender and yarrow, should be picked just before they fully open. The flowers are more likely to lose their petals if you harvest them after they are completely open. But if you cut them before they are fully open, they will continue to open in the vase. Harvest flowers early in the day and transfer the stems to a vase or glass of water until you're ready to use them.
Most roots—including those of astragalus (Astragalus membranaceus), burdock (Arctium lappa), dong quai (Angelica sinensis), and echinacea (Echinacea spp.)—should be dug and harvested from mature plants at the end of the growing season, after a plant's leaves have yellowed and begun to die back. The roots of horseradish (Armoracia rusticana) are best dug when they are younger, before their flavor becomes too strong and their texture too coarse. Harvest roots using a garden fork: Carefully lift the root, then cut it away from the rest of the plant. Rinse roots with water, blot them dry, and then store them in a dry, well-ventilated area.
Plants that grow on long stems—basil, cilantro and chives, for instance—are usually fairly free of soil or sand and so are relatively easy to clean before using. However, those that creep along the ground, such as thyme and oregano, can easily collect sand or mud on their leaves and stems, making them trickier to clean. In addition, herbs with crinkled leaves and those suffering from pest problems should be cleaned thoroughly under running water.
To remove grit, dust or other residue, rinse the leaves under cold running water for a minute or two. Or fill your sink with cold water and immerse the herbs in the water. Swish them around, which will cause the debris to drop to the bottom of the sink. Repeat if necessary, then gently pat them dry.
Reprinted from Rodale’s 21st Century Herbal by Dr Michael Balick. Copyright (c) 2014 by Rodale Inc. By permission of Rodale Books. Available wherever books are sold.