Propagating Herbs and Perennials
(1) Growing Herbs at Home
Agricultural publication G06470 Revised December 15, 1997 Ray R. Rothenberger, Dept. of Horticulture, Univ. of Missouri-Columbia
Propagation: cutting, division, 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. You can propagate lavender, lemon balm, scented geraniums, sage and rosemary from cuttings. Information about taking cuttings and rooting them is available in MU publications G 6560, Home Propagation of House Plants, and G 6970, Home Propagation of Garden and Landscape Plants.
You can take cuttings of herbs any time during late spring and summer from healthy, well-established plants. Those 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 on a sunny window or in a coldframe. 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 plants 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.
Department of Horticulture, University of Missouri-Columbia
(2) Propagating Herbaceous Perennials Contact: Diane Relf, Extension Specialist, Environmental Horticulture Posted April 1997
(Prepared by Jennifer Shuster, Extension Technician, Consumer Horticulture, Virginia Tech Extension, Blacksburg, VA 24061-0327.) One of the joys of a perennial garden is watching the plants grow and fill out the spaces allotted to them. However, herbaceous perennials can outgrow their alloted space so they need to be divided periodically, discarding the older center growth and replanting only the strong growth from the outer edge of the clump. This 'invigorates' the plants with the additional benefit of creating more plants for yourself and to share.
To divide a plant with a root mass such as yarrow or shasta daisies, insert two spading forks back to back into the clump and bring the fork handles together, prying the clumps apart. Don't be afraid of breaking the roots. This is a necessary evil in the process of breaking up the clump. As long as you have root and stems on each piece you can break up a clump into as many pieces as you want.
A rhizome, unlike a root, is an underground stem. It bears roots but also has prominent leaf buds or eyes. Many perennials produce rhizomes: Achimenes, Helleborus, and Hosta. Dig up the rhizome and, using a clean sharp knife, cut off pieces which bear one or two eyes. Dust the cut ends with a fungicide or a rooting powder containing a fungicide to prevent rot or disease before replanting the pieces.
Divide fall-flowering plants in the spring, and spring and summer flowering plants in the fall. The frequency of division depends on the plant itself. For example, Monarda and Oenothera should be divided every two or three years. Phlox, Astilbe, Hemerocallis, and Physostegia should be divided only every three or four years.
Stem cuttings are frequently used for propagating the low growing shrubby perennials such as Phlox and Penstemon as well as the foliage perennials like Sedum and Veronica. Cuttings should be made in mid-summer from spring blooming plants like Phlox and in late spring from summer and autumn flowering plants like Sedum. Take cuttings of 2 to 3 inches in length in early or mid-morning. Dip these in a root-promoting hormone and plant into rooting medium. The cuttings may be kept out-of-doors in a shady, protected spot where they can be kept moist. After top growth extends several inches, the plants can be set into permanent garden locations.
You can also propagate certain plants by bending a branch down and covering with soil. The part of the stem which is buried will produce new roots. Hardy periwinkle, St.-John's-Wort, and several other creeping perennials will propagate this way.
It is an enjoyable, intriguing and gratifying experience to propagate perennials on your own. It requires no elaborate or expensive equipment, just time and patience on your part.
Search on Virginia Tech Extension Serv., Information Resources for your topic.
Propagation by Layering: Instructions for the Home Gardener
Stems that are still attached to their parent plant may form roots where they come in contact with a rooting medium. This method of vegetative propagation is generally successful, because water stress is minimized and carbohydrate and mineral nutrient levels are high. The development of roots on a stem while the stem is still attached to the parent plant is called layering. A layer is the rooted stem following detachment (removal) from the parent plant.
Some plants propagate naturally by layering, but sometimes plant propagators assist the process. Layering is enhanced by wounding the stem where the roots are to form. The rooting medium should always provide aeration and a constant supply of moisture.
Types of Layering
Simple layering can be accomplished by bending a low growing, flexible stem to the ground. Cover part of it with soil, leaving the remaining 6 to 12 inches above the soil. Bend the tip into a vertical position and stake in place (Figure 1). The sharp bend will often induce rooting, but wounding the lower side of the bent branch may help also. Simple layering can be done on most plants with low-growing branches. Examples of plants propagated by simple layering include climbing roses, forsythia, rhododendron, honeysuckle, boxwood, azalea, and wax myrtle.
Simple layering can be done in early spring using a dormant branch, or in late summer using a mature branch. Periodically check for adequate moisture and for the formation of roots. It may take one or more seasons before the layer is ready to be removed for transplanting.
Tip layering is quite similar to simple layering. Dig a hole 3 to 4 inches deep. Insert the tip of a current seasons shoot and cover it with soil. The tip grows downward first, then bends sharply and grows upward. Roots form at the bend. The re-curved tip becomes a new plant (Figure 2). Remove the tip layer and plant it in late fall or early spring. Examples of plants propagated by tip layering include purple and black raspberries, and trailing blackberries.
Compound (serpentine) layering is similar to simple layering, but several layers can result from a single stem. Bend the stem to the rooting medium as for simple layering, but alternately cover and expose sections of the stem. Each section should have at least one bud exposed and one bud covered with soil. Wound the lower side of each stem section to be covered (Figure 3). This method works well for plants producing vine-like growth such as heart-leaf philodendron, pothos, wisteria, clematis, and grapes.
Mound (stool) layering is useful with heavy-stemmed, closely branched shrubs and rootstocks of tree fruits. Cut the plant back to 1 inch above the soil surface in the dormant season. Dormant buds will produce new shoots in the spring. Mound soil over the new shoots as they grow (Figure 4). Roots will develop at the bases of the young shoots. Remove the layers in the dormant season. Mound layering works well on apple rootstocks, spirea, quince, daphne, magnolia, and cotoneaster.
Air layering can be used to propagate large, overgrown house plants such as rubber plant, croton, or dieffenbachia that have lost most of their lower leaves. Woody ornamentals such as azalea, camellia, magnolia, oleander, and holly can also be propagated by air layering. For optimum rooting, make air layers in the spring on shoots produced during the previous season or in mid to late summer on shoots from the current seasons growth. For woody plants, stems of pencil size diameter or larger are best. Choose an area just below a node and remove leaves and twigs on the stem 3 to 4 inches above and below this point. This is normally done on a stem about 1 foot from the tip.
Air layering differs, depending on whether the plant is a monocot or a dicot. For monocots, make an upward 1- to 1 1/2-inch cut about one-third through the stem. The cut is held open with a toothpick or wooden match stick. Surround the wound with moist, unmilled sphagnum moss (about a handful) that has been soaked in water and squeezed to remove excess moisture. Wrap the moss with plastic and hold in place with twist ties or electricians tape. No moss should extend beyond the ends of the plastic. Fasten each end of the plastic securely, to retain moisture and to prevent water from entering. If exposed to the sun, the plastic should be covered. Aluminum foil can also be used, as it does not require twist ties or tape to hold it in place.
The process for dicots is similar, except a 1-inch ring of bark is removed from the stem. With a sharp knife, make two parallel cuts about an inch apart around the stem and through the bark and cambium layer (Figure 5). Connect the two parallel cuts with one long cut. Remove the ring of bark, leaving the inner woody tissue exposed. Scrape the newly bared ring to remove the cambial tissue to prevent a bridge of callus tissue from forming. Application of a root-promoting substance to the exposed wound is sometimes beneficial. Wrap and cover using the same procedure as that described for monocots.
After the rooting medium is filled with roots, sever the stem below the medium and pot the layer. The new plant will usually require some pampering until the root system becomes more developed. Provide shade and adequate moisture until the plant is well established.
Natural Forms of Layering
Sometimes layering occurs naturally, without the assistance of a propagator. Runners and offsets are specialized plant structures that facilitate propagation by layering.
A runner produces new shoots where it touches the growing medium (Figure 6). Plants that produce stolons or runners are propagated by severing the new plants from their parent stems. Plantlets at the tips of runners may be rooted while still attached to the parent or detached and placed in a rooting medium. Examples include strawberry and spider plant.
Plants with rosetted stems often reproduce by forming new shoots, called offshoots, at their base or in the leaf axles. Sever the new shoots from the parent plant after they have developed their own root systems. Unrooted offsets of some species may be removed and placed in a rooting medium. Some of these must be cut off, whereas others may simply be lifted from the parent stem. Examples include date palm, bromeliads, and many cacti.
For Further Reading
Search for your topic at North Carolina Extension Service