Although there are some herbs that may be collected year round, most have a particular growing season and must be harvested and either used immediately or preserved for use in the following year. Herbs need to be processed quickly to prevent deterioration and retain their healing action.
Harvesting from the Wild
Wild plants offer a free and natural source of herbal remedies. Furthermore, active constituents are often more highly concentrated in wild plants since the herb is likely to be growing in its preferred habitat.
Proper identification of wild plants is essential. Use a field or wildflower guide to help you. If in doubt, do not pick the plant, as poisoning can result from misidentification.
Ecological & Legal Factors
While common species, such as nettle (Urtica dioica), may be readily harvested from the wild, many rarer species are under great pressure due to the lack of a suitable habitat. In many countries it is illegal to uproot any wild plant, and certain species may be protected. Although gathering medicinal plants such as gentian (Gentiana lutea) may be legal in some countries, it will only reduce their future chances of survival in the wild. Never pick rare or uncommon plants from the wild, even if they are locally plentiful, and do not collect more than you will use. Do not harvest bark from the wild.
Before harvesting, consider where the plant is growing and whether it could be contaminated by pollution. Do not collect from roadsides, close to factories, or in areas where crop spraying has occurred.
Harvesting from Your Garden
Cultivated herbs provide a ready supply of fresh material in a controlled environment. Cut perennials carefully so that plants can quickly regrow. Some plants, such as lemon balm (Melissa officinalis), provide two or more crops per year.
Harvesting medicinal herbs requires careful planning to ensure the parts are processed in peak condition and fast enough to retain their active ingredients.
Ideally, use a wooden tray or open basket for collecting herbs. This prevents the plant being crushed. In the wild, a non-nylon rucksack or sack may be more appropriate. Always cut with a sharp knife or scissors to minimize damage to the plant and try to handle plants as little as possible. Wear gloves if gathering prickly or allergenic plants, such as rue (Ruta graveolens).
What to Look For
Collect material from healthy plants, free from insect damage and pollution. It is important to discard damaged plants because they can lead to disease or decay in dried plant material. Do not mix cut plant material to avoid mistakes in identification.
When to Harvest
Gather herbs in dry weather, preferably on a sunny morning after the dew has evaporated. Picking when the plant is at its peak of maturity ensures that it will have a high concentration of active constituents. Usually, leaves are best collected as they open during the spring or summer months, flowers as they start to bloom, fruit and berries just as they become ripe, and roots in the autumn once the plant has drawn its vitality back beneath ground. Bark must be gathered with great care if the shrub or tree is to survive—in most cases, harvest it in spring or autumn.
The Correct Medicinal Part
In many cases, different parts of the same plant, for example the leaves and seeds, can have quite different actions and uses. Make sure that you harvest the correct medicinal part of the plant for your purposes.
Only collect plant material that you will be able to use or process immediately after harvesting. This is because fresh plant material deteriorates very quickly and the medicinally active constituents are often the first to be affected. In particular, aromatic herbs can lose their volatile oils within hours. Salad leaves and culinary herbs are best eaten right away to make the most of their nutrients, although they can be stored for a few days in a plastic bag filled with air in a refrigerator.
It is vital to store dried herbs properly or they will not last. Leaves, flowers, roots, and other parts should be stored in sterilized, dark glass containers with airtight lids. They may also be stored in new brown paper bags, which must be kept dry and away from light. Metal and plastic containers are inadvisable because they may contaminate the herb. If stored in a cool, dark place, herbs can be kept for about 12 months after harvesting. Herbs frozen in plastic bags can be used for up to 6 months. Label the container with the herb, source, date of harvesting, and strength of preparation if appropriate. Watch out for insect infestation. If this occurs, discard all affected material and sterilize the container.
Herbs can be preserved in a number of ways, the simplest being air or oven drying. A warm, dry place such as an airing cupboard is ideal. Use plain paper for drying herbs, never printed newspaper. Dried herbs can be stored for many months in a dark glass jar or a brown paper bag.
These include all the parts of the plant growing above ground—stems, leaves, flowers, berries, and seeds. The stems are normally cut 2–4 in (5 –10 cm) above ground shortly after the plant has begun to flower, when it is putting most effort into growth. Perennials may be cut higher above ground to encourage further crops. Remove and dry large flowers and leaves separately; smaller ones can be dried on the stem.
- Hang bunches of about 8–10 stems in a warm (but not hot), well-ventilated, dark place. Ensure that the stems and leaves are not too tightly packed together to enable air to circulate freely around them.
- Once brittle but not bone dry, separate small stems, leaves, flowers, and seeds from the stems by rubbing the bunches over a large sheet of plain paper.
- Carefully pour the dried material into a dark glass jar or a brown paper bag.
In most cases, flowers are picked just after they have opened. Sometimes only specific parts of the flower are used, such as the petals of calendula (Calendula officinalis), while other flowers are used whole.
- Separate large flower heads from stems and remove any insects or dirt. Place the flowers on absorbent paper on a tray in a dry place, allowing sufficient room between them for air to circulate.
- Once dry, store flower heads in a brown paper bag or dark glass jar. Remove calendula petals from the central part of the flower before storing.
Small blooms can be picked with the stalk attached and separated later. Hang small flowers, such as lavender (Lavandula officinalis), upside down in a paper bag, or suspended over a tray (see drying seeds below). If the stems are fleshy, dry as for large flowers, above.
Fruit & Berries
Harvest fruit and berries in early autumn when ripe but still firm. If left to become over-ripe, they may not dry properly. They can be picked individually or in bunches.
- Place berries or fruit on absorbent paper on trays. Put in a warmed oven (turned off) with the door ajar for 3–4 hours. Move to a dry, warm, dark site and turn occasionally. Discard any moldy berries or fruit.
Roots, Rhizomes, Tubers, & Bulbs
The underground parts of the plant are usually gathered in autumn after the aerial parts have withered or become inactive and before the soil is waterlogged or frozen. Many roots may also be collected in early spring before the aerial parts begin to grow. Dig deeply around the root, prying it out of the ground. Some tap roots are difficult to uproot completely. Remove the required amount and replant the remaining root.
- Shake off any soil and wash thoroughly in warm water, removing any small, unwanted side roots or damaged soft spots. Chop into small slices or pieces with a sharp knife.
- Spread out the root pieces on absorbent paper on a tray and place in a warmed oven (turned off) with the door ajar for 2–3 hours. Move to a warm place until dry.
Collect ripe seed pods, capsules, or flowering stems in late summer before the seeds have been scattered.
- For tiny seeds, hang small bunches of seedheads upside down over a paper-lined tray, or place in a paper bag. Allow to dry and gently shake. Remove larger seeds by hand when dry.
Sap & Gel
Only harvest sap from your own garden. Collect sap in the spring as it rises, or as it falls in the autumn. Trees such as silver birch (Betula pendula) produce huge quantities of sap if tapped, although this reduces the tree’s vitality. Bore a deep hole into the trunk—no more than a quarter of its diameter—and place a collecting cup under the hole. In spring, quarts of sap may be produced, and it is essential to stop the hole with resin or wood filler after about a quart (liter) of fluid has been removed. Collect milky juices or latex from plants such as dandelion (Taraxacum officinale) by squeezing the stems over a bowl. Wear gloves, because latex or sap can be corrosive. The gel from aloe vera (Aloe vera) is scraped out after slicing the leaf lengthwise and peeling back the edges.
Only harvest bark from your own shrubs or trees as it carries the risk of losing the whole plant through overstripping or “ringing” (removing a whole band of bark). It is best to collect bark from outlying branches, which can then be pruned back. If stripping bark from a plant, gather it in autumn when the sap is falling. Remove insects, lichen, and moss from the bark, cut it into small pieces, and place it on a tray to dry.
Other Ways to Preserve Herbs
Apart from simply air-drying herbs, there are a number of other ways to preserve their medicinal benefits.
An effective but expensive way to dry herbs is to use a dehumidifier, which literally sucks water out of the plant. The dehumidifier should be placed in a more or less sealed small room in which the herbs are hung in loose bunches or placed on mesh trays.
Freeze-drying retains color and flavor but is more suited to culinary than to medicinal herbs. Whole sprigs of herbs can be frozen in plastic bags. There is no need to defrost before use as the leaves crumble easily when still frozen. Chickweed (Stellaria media) can also be frozen and used topically for itchy and weeping skin conditions. Many plants may be juiced, frozen as ice cubes, and thawed as required.
It is possible to dry herbs in a microwave oven, though this is not recommended. The cut parts should be spread out on kitchen paper and dried in the microwave according to the manufacturer’s guidelines.