In most cases herbs are used fresh, but there are times when it?s handy to have a supply of dried herbs on hand. It?s not difficult to dry herbs, but it is critical to pick them at the right time. The oils and other chemicals, which make a herb valuable, in most cases, are at their best at only one stage of the plant?s growth. Medicinal herbs, in particular, can lose much of their value if harvested too early or late.
Foliage, flowers, fruit, seed, bark, and even roots, rhizomes and bulbs, are harvested from herbs. No matter which part you harvest, the basic procedure is usually the same:
- Cut off the required parts with clean, sharp tools (avoid bruising).
- Harvest in cool weather.
- Remove as much unwanted material (eg: soil, insects, etc.) while still outside.
- Clean the material as soon as possible, removing damaged, dead or marked tissue, and any foreign material including insects and soil. Avoid washing, which might remove oils. Avoid using diseased material.
- Process the material as soon as possible (eg. distillation, drying, etc.), to minimise loss of oils or other chemicals.
Most herb leaves are used fresh, although drying is used to ensure supply when leaves are not available, such as out of season. For most perennial herbs, the leaves are best-harvested before flowering, as they can lose up to 60% of their vegetative mass once the flowers form (e.g. mint).
Those herbs, which are used for both flowers and leaves (e.g. chamomile for use as a tea or scented geraniums and lavender for use in pot pourris) should be harvested when the plants are at the peak of their flowering.
They should ideally be cut mid-morning, after any dew has gone, on a clear, dry day. They are best dried in a shaded position. Air drying is normally adequate.
Roots are normally dug in autumn and dried whole. Extra large roots may be sliced first then the slices are dried. Artificial heat is desirable for root drying.
With most seed harvesting it is best to harvest in the early stages of ripening to avoid unnecessary losses from seed drop, and also to preserve maximum oil content and colour in the harvested product. Seeds are ready to harvest when a slight tap on the seed head causes the seed to fall. Seeds harvested for culinary use may also be used for planting the next crop, provided viability is good.
Shade drying is preferable; though in commercial production, plants are often mowed then field cured or ripened on canvas sheets.
Harvesting material for medicinal use
The demand for pure, clean, properly handled material is high, both in Australia and throughout many other parts of the world. It is critical that the herbs are of the highest quality and are picked at the optimum stage of production. LEAVES should ideally be collected on clear days, mid-morning, after the dew has dried. For most medicinal plants, harvest the leaves when the plant is starting to flower. Leaves of biennial plants are best collected in the second year of growth. To dry, spread the leaves out on a clean dry surface. Turn occasionally until thoroughly dry. Remove stems from the leaves and only keep those leaves which have retained their natural colour.
FLOWERS should be collected immediately after they open. Dry the same way as for leaves and only retain those that keep their natural colour.
BULBS should be collected immediately after the leaves of the plant die back. Remove the outer scales of the bulb, slice it, then dry it using artificial heat.
BARKS are commonly collected in autumn or spring. It is normally the inner bark which is required (remove the outer bark first). Most barks should be dried in sunlight (but not wild cherry).
SEEDS should be gathered on ripening (but before the seeds are expelled or fruits are eaten). Larger, fully developed seeds are the most useful.
HANDLING FRESH HERBS AFTER HARVEST
Once picked, most fresh herbs deteriorate quickly unless properly handled. They will quickly wilt, and lose colour, essential oils and other aromatic compounds. This deterioration can be slowed in a number of ways:
? Plants grown under optimum temperature and soil moisture conditions don't deteriorate as fast. In other words the healthier and more vigorous the plant is when harvested, the longer it will last.
? If harvested when the aromatic compounds, oils, etc are at optimum levels, deterioration is slower. In some plants, including rosemary and sage, this is just before flowering; for other plants the optimum harvest time may be at a different stage of the plant's growth.
? A 10oC reduction in the temperature of the harvested herb will generally increase its storage life by 3 to 4 times.
? Most fresh herbs are best stored at refrigerator temperatures of around 1 - 4oC. Some herbs (eg. watercress and basil) are sensitive to chilling and should not be stored at this low a temperature (around 5 oC to 6oC would be preferable).
? Harvesting your herbs in the coolest part of the morning will also help get them down to storage temperature more quickly.
? Do not store at temperatures below 1oC as damage due to freezing will occur.
? Water loss is reduced if high humidity is maintained around the fresh herb - do this with film wraps. You do not want humidity too high though. If condensation develops on plant tissues, the humidity is too high and breather holes in the plastic will be needed otherwise the herb may rot.
? Fresh herbs are often very soft and can be readily damaged during harvesting (e.g. mint, basil and coriander). This makes them more prone to moisture loss, to discolouring and microbial infection. Careful handling during harvest to reduce damage will prolong their storage life.
Anyone can dry herbs. All you need is a cool, preferably dark, reasonably well ventilated room. Your harvest is simply tied in bunches and hung upside down from the ceiling (or even curtain rods). Don't do this in a room which will steam up (ie. avoid kitchens and bathrooms), and try to find a relatively dark place as direct sunlight can reduce oil content.
In very humid climates, bunches will take longer to dry and may develop fungal growths. To minimise such problems be sure to use a well-ventilated room (a fan may be helpful), keep the bunches smaller and allow room for air to move between bunches.
After drying, foliage can be stripped and either used or stored in sealed, dry containers. Roots (and sometimes other parts) are often ground into a powder after drying. Containers should be labelled with the name of the plant and when it was harvested to avoid any confusion.
Oven drying greatly hastens the drying process. Preheat the oven to 50oC. Place the herbs on brown paper on oven racks and poke some slits in the paper to increase air movement. The oven door should be left slightly open to allow moisture to escape. Leave the herbs for one hour, before turning and leaving for another hour. By the time they are taken out of the oven, they should be crisp and dry with reasonable colour.
This is the fastest drying method. Place the herbs between paper towels and microwave them on high for 1-2 minutes, depending on how high the herbs? moisture content. It may take a few practice runs to determine the right time period for drying using a microwave.
HARVEST OF SELECTED HERBS
Basil: Cut stems close to the ground about flowering time, then treat like mint. Regrowth will provide one or two additional crops in a season.
Chervil: Fresh leaves can be harvested and used like parsley. Seeds can also be used for culinary purposes (e.g. flavouring vinegar).
Fennel: Foliage is simply cut, dried, then crumbled. Seed can also be harvested.
Fenugreek: Fruits picked as soon as ripe, before seed pods shatter. Seeds are shelled or threshed from pods, then dried using artificial heat.
Lemon Verbena: Leaves are picked individually and dried.
Lovage: Leaves are picked while young, thin and tender, then dried. Roots are dug in late autumn of the second year, washed, sliced then dried
Mint: Shoots are cut just before flowering on a dry day and air-dried in shaded conditions. Leaves are stripped after drying and stems discarded.
Parsley: Foliage is handled like mint. Seed heads are harvested on maturity and laid on a dry surface, dried, then beaten or thrashed to obtain seed. Roots are occasionally dug (autumn of second year) and dried.
Rue: Used mainly fresh, but may be dried.
Sage: Tender herbaceous parts can be cut and handled like mint. Only one cut should be done in the first year, but two or three each year after that. Plants become increasingly woody over the years, and are usually replaced after 5 to 6 years.
Summer Savoury: Cut at ground level when flowering starts, and treat like mint.
Sweet Marjoram: Normally used fresh, but can be fried.
Tansy: Cut in full bloom. Air dry leaves and flowers in shade. Discard stems after drying.
Thyme: Cut when flowering and air dry. Flowers and leaves can be powdered or chopped…discard coarse stems. Two or three harvests in a season can normally be made.
Winter Savoury: Cutting stimulates growth ? normally cut twice or more each year.