In a botanical sense, an herb is a plant that does not produce a woody stem and dies back to the ground each winter to a perennial root system. In the garden sense, herbs are plants that serve as a major source of seasonings in food preparation. In an even broader sense, herbs include plants that are also useful for scents in cosmetics or for medicinal purposes. Some of them are woody and out step the definition of a herbaceous plant.
For American pioneers, herbs were the major source of seasonings for foods. They were also used for curing illnesses, storing with linens, strewing on floors, covering the bad taste of meats before refrigeration was devised, dyeing homespun fabrics, and as fragrances.
With the advent of the supermarket, growing herbs in the garden declined because a wide range of dried herbs became available in stores. Now, however, with an increase in the popularity of ethnic foods, combined with a realization that fresh herbs have more distinctive tastes than some dried herbs, more gardeners are growing at least a few herbs for fresh use, drying or freezing. Increasing interest in herbal medicine also has helped make herb growing more popular. In addition, some herbs are ornamental.
Most herbs are easy to grow, but you must select the proper location to grow them. Most herbs need a sunny location, and only a few, including angelica, woodruff and sweet cicely, are better grown in partial shade. The oils, which account for the herbs' flavor, are produced in the greatest quantity when plants receive six to eight hours of full sunlight each day. If you don't have a good, sunny location, many herbs will tolerate light shade, but their growth and quality will not be as good.
Herbs will grow in any good garden soil. The soil should not be extremely acid or alkaline; a soil nearly neutral is best for most herbs. A pH between 6.5 and 7.0 produces the best herbs. Herbs grow best when soils have adequate organic matter. Most herbs do not require highly fertile soil. Highly fertile soils tend to produce excessive foliage that is poor in flavor.
In preparing average soils, incorporate 4 inches of peat moss or compost into the garden area to improve soil condition and help retain moisture.
When selecting a site for an herb garden, you must consider drainage. None of the important herbs grow in wet soils, but a few, such as mint, angelica and lovage, thrive in fairly moist soils.
If the only area available is poorly drained, you need to modify the area. Build raised beds or install underground drainage tiles to grow herbs successfully.
Once you select a site, cultivate the soil to a depth of 12 to 18 inches, then level it. If only a shallow layer of topsoil exists above hard subsoil, remove the topsoil temporarily. Break up the subsoil, adding organic matter. After improving the subsoil, put it back. Even though the topsoil may be better than the subsoil, the topsoil may also need additional organic matter.
Few insects or diseases attack herbs. In some localities, rusts infect mints. In hot, dry weather, spider mites damage some herbs.
Aphids attack anise, caraway, dill and fennel. Grasshoppers and certain caterpillars attack herbs when conditions are right. Control is usually not necessary until you notice a problem. If control is warranted and pesticides are used, make certain they are labeled for food crops if the herbs are to be used for culinary purposes.
Propagation From Seeds
You can grow many herbs from seeds. If possible, sow the seeds in pots or flats indoors in late winter. They need a sunny window and cool temperatures (60 degrees F) for best growth. Treat young plants for the garden just as you would treat young salvia or pepper plants.
Because some plants take longer than others to develop, start those with smaller seeds first, preferably in February. You may later transplant them into individual pots and plant them in the garden after danger of frost is past. The finer the seeds, the shallower you should sow them.
A few herbs do not transplant well. Sow them directly into the garden. Plant anise, coriander, dill and fennel directly in the garden and don't transplant them.
For direct seeding outdoors, plant in spring after all danger of frost is past and the soil is beginning to warm up. Make the soil into a fine, level seed bed. As a general rule, sow seeds at a depth of twice their diameter.
Propagation From Cutting, Division and Layering
Some established herbs multiply asexually by cutting, division or layering.
Layering is suitable for many perennials with flexible branches. Division works well for tarragon, chives and mint. Lavender, lemon balm, scented geraniums, sage and rosemary can be propagated from cuttings.
You can take cuttings of herbs any time during late spring and summer from healthy, well-established plants. Cuttings taken in fall take longer to root. Healthy tip growth makes the best cuttings. Cuttings of vigorous soft shoots or old woody stems are less desirable.
Cut just below a node to form a cutting that is 3 to 5 inches long. Most herbs should root in two to four weeks. After rooting, overwinter them indoors in pots in a sunny window or in a cold frame. Plant them outdoors in a permanent location the following spring.
Division is useful for multiplying healthy, established plants that may be two to four years old. Division allows modest increase for plant like chives, mints and French tarragon. Divide herbs in early spring before growth begins. Dig up the old plant and cut or pull it apart into sections. Replant the sections and keep them moist until the new plants are established.
Layering is the simplest and most reliable method to increase perennial herbs such as thyme, lemon balm, winter savory, sage, bay and rosemary. The basic principle is to produce roots on a stem while it is still attached to the parent plant. After you root the stem, detach the new plant from the parent. Select a healthy branch that is growing close to the ground and that is flexible enough to bend down to the soil. While holding the branch close to the soil, bend the top 6 to 10 inches of the stem into a vertical position. It may be helpful to scrape the bark on the underside of the branch at the bend. Bury the bent, scraped portion 3 to 6 inches deep, and anchor it with a wire loop. Insert a small stake to hold the top upright. Water thoroughly.
You can layer anytime from spring to late summer. Allow the rooted shoot to remain in place until the following spring. Then cut it from the parent plant and plant it into the desired location.
Many herbs suffer winter damage in our climate, so some winter protection for perennial herbs is advisable. Many herbs have shallow roots that heave out during spring thawing and freezing of soil. A loose mulch spread over the roots about 4 inches deep can provide adequate protection. Evergreen boughs, straw or oak leaves are good materials for a mulch. Don't mulch until after the ground is frozen in early winter. Do not remove mulch until you see signs of new growth in the early spring. If the mulch compacts during the winter from heavy snows, fluff it up in early spring before growth begins.
Depending on the herb, harvest may include one or more plant parts. In most cases you harvest the leaves, but in some cases you pick flowers, seeds or roots. Handle blossoms just as you would handle leaves. Often, you harvest blossoms with the leaves and mix them together. Dried herbs lose quality in two to three years. Discard them if you haven't used them in that time.
To determine the best harvest time for each herb, you need some experience. However, a few general rules can lead you in the right direction for most herbs. Harvest the leaves when they contain the optimum amount of essential oils. These oils give herbs their special flavor or scent. Ideally you should cut herbs soon after the dew has evaporated from the leaves in the morning. Harvest on a dry day that has been preceded by at least two sunny days.
In most cases, cut stems for harvest when the flower buds are just beginning to open. Mints, however, have the most oil in the leaves when the spikes are in full bloom.
When gathering a large quantity of herbs, use an open-weave basket or containers that allow good air movement. Don't stuff herbs into plastic bags, which can heat up and cause rapid deterioration of herbs. Never cut more stems than you can conveniently dry at one time. You can cut back a perennial herb to about half its height and can cut down an annual to a few inches. You can also remove an annual completely near the end of the season.
Wash the plants in cool water immediately after gathering and spread them on towels. Pat them gently with a towel until dry. A dark, well-ventilated room where temperatures run between 70 and 90 degrees F is an excellent room for drying. Air conditioning is helpful, because it reduces humidity in the air. You can use frames covered with cheesecloth or other netting, or metal window screens with cheesecloth laid on top for drying. Prepare the frames or screens before you cut the plants.
For some herbs, you strip the leaves from the stems before drying. Herbs in this group include basil, dill, lemon balm, lovage, mint, sage, lemon verbena and tarragon. Spread these leaves in single layers for quickest drying.
Herbs with smaller leaves can be dried on the stems. These herbs include thyme, summer and winter savory, rosemary, oregano and marjoram. Strip the leaves after drying is complete.
Herb leaves should dry in three to four days under proper conditions. In humid weather, you may need to spread the herbs on a cookie sheet and dry them in an oven at about 125 degrees F for a few minutes before placing them in an airtight container.
Some herbs do not dry well at home. Instead, you can freeze them. Handle them as you would for drying. Then after washing, blanch them in boiling, unsalted water for 50 seconds, cool quickly in ice water and blot dry. Spread them in a single layer on paper or cookie sheets and place them in the freezer.
You can freeze dill, chives and basil without blanching. After the herbs are frozen, place them in airtight plastic containers or bags.
Angelica and lovage produce usable roots. Dig these roots in the late fall or early spring. Wash them thoroughly after digging. Then slice or split the large roots. Place the pieces in thin layers on screens and turn the slices several times a week. After they are partially dry, finish them in an oven at low heat before placing them in an airtight container for storage. It may take roots six to eight weeks to dry completely. When dry, the root piece should snap when you bend it.
You can grow and process seeds of dill, caraway, fennel and anise at home. When the plants begin to mature and yellow, cut the heads of the plants containing the seeds, leaving a short stem. Place them on a drying tray for five or six days. Then the seeds should fall fairly easily from the heads. Remove the chaff, and allow the seeds to continue to dry for another week. Stir them frequently. Store seeds in airtight jars after complete drying.
Source: University of Missouri Extension
Web site http://extension.missouri.edu/p/g6470