Herb Propagation
Herbs are generally propagated 4 ways, either by seed, cuttings, division, or by layering. Different herbs can be propagated by any or all of these methods.
Seed
Some perennial and most annual herbs may be started from seed. To start from seed, you require a reliable seed source, a soil-less seed start mixture, and several small plastic trays (typically 48 wells) with plastic inserts.
First, fill the plastic inserts with the soil-less medium, water thoroughly, and place in the carrying tray. Thinly sow the seed on top and cover more soil-less medium, at twice the seed thickness. Gently tamp down and spray surface with water -- do not soak, just wet. Appropriately label the seeded tray, cover with a plastic dome or damp newspaper, and place in a warm dark place.
Check twice daily for signs of sprouting and do not allow to dry out. When sprouted, slowly expose the tray to light over the next couple of days. You may then place the tray under fluorescent lights not more than 4 inches above seedlings or place in a sunny window. Herbs require 5 to 7 hours of direct light daily. When seedlings are approximately 4 inches tall, they are ready to be transplanted outside or into a larger container. If germination is slow and irregular try applying some heat to the bottom of the seeded flat-place on top of fridge or use a rooting box (outlined under Cuttings, below).
Cuttings
Most perennial herbs may be propagated by rooted cuttings. This is usually done in the spring when the plants are in a vigorous stage of growth. NOTE: It is important to work quickly so the cuttings do not become wilted before being transplanted. It is also a good idea to have ready small pots, approximately 2 to 3 inches deep. Fill with thoroughly watered soil-less medium and root stimulating hormone, if desired. Also have ready a small container of alcohol to disinfect your cutting tool between cuttings.
Using a sharp clean knife or scissors, cut between 3 to 4 inches of new growth from a healthy stem, usually just above or below a node or leaf. After taking 10 to 15 cuttings, seek refuge in a shaded potting area and prepare your cuttings.
First, carefully remove all leaves from the lower half of the cutting using sharp scissors or a knife, or by sliding your thumb and index finger down the stem. Dip the cut end into root stimulating hormone, if desired, and stick the cutting into the prepared pot so that the leaves almost touch the surface. A pencil or plant dibble will also accomplish this goal.
Repeat this process for all the cuttings you have. Place finished pots in a leak-proof carrying tray. At this point you will want to use a rooting box -- basically a box that holds flats of plants over a heat source. It is quite easy to build yourself by using an old wooden crate and placing it over a 25 watt light bulb in a suitable electrical fixture. Bottom heat greatly encourages root growth. The temperature in the rooting box should be 23 - 28°C.
Following this, place your rooting box in a shaded, cool, humid area (approximately 16 - 18°C) and place your carrying tray on top. It is important to constantly mist the cuttings so the leaves do not wilt and you will need to do this several times daily. After approximately 10 days, gently tap one or two of the cuttings out to check for root growth. By this point you should see them starting, but it will take about 21 days for sufficient roots to form for the plant to be ready to be transplanted to the garden. At this point there should be enough roots developed to hold the growing medium together. Plants are also ready for transplant when you start to see new top growth.
Division
This is generally the fastest way to achieve mature plants. Early spring and fall are the best times to do divisions and dividing herbs often has other benefits -- it will discourage disease by thinning foliage and controlling unwanted spreading.
You will only need a spade and a sharp knife for this project. First, carefully dig around the circumference of the plant and pry the entire plant from the ground. Lay the plant on the ground in the shade and massage the dirt away from the roots or wash off with a hose. With a sharp knife, divide the mass of roots / stolons / rhizomes into fragments that have several new buds each and replant where desired.
It is best to do this procedure on a cool day to provide as little stress as possible to the roots.
Layering
This is by far the simplest propagation method and many perennial herbs perform layering without prompting. A stem touches moist ground and, before you know it, the stem has put down new roots. When this happens naturally, ensure there are sufficient new roots and then, using a sharp knife, sever the new plant from its mother. Carefully dig up and move it to its new location.
Upright, woody stemmed herbs with flexible branches can also be layered. Select a stem near the ground that is young and flexible. Beginning at a point 3 to 4 inches from the tip, strip about 5 inches of foliage off the stem. Using a sharp knife, scrape the thin bark off 2 to 3 inches of the underside of the leafless stem. This process is called wounding and appears to accelerate the rooting process.
Dig a small hole 2 to 3 inches deep with gently sloping sides below the prepared stem and carefully lay the branch in the hole (it may be necessary to peg it in place with a u-shaped wire) and cover with soil. If your soil is very heavy, you may want to add some peatmoss to allow for good aeration. Mulch the area or water regularly to keep moist.
Layered stems may form roots in several weeks or months -- this is not a method for the inpatient gardener. When a gentle tug on the stem meets with some resistance, the stem has probably rooted and calls for a careful visual inspection. When the plant is ready, gently snip free and, gently, lift by the roots to its new location.
See Herbs - Introduction, for additional general herbal information.
