Some herbs can be grown from seed, others demand to be dug and divided, and then there are those that are best propagated by persuading a stem to transform itself into a rooted plant. This is often done by rooting cuttings, but the technique called layering — in which stems are coaxed to produce roots while they are still attached to the parent plant — should be in every herb grower’s bag of tricks.
“Layering takes advantage of the plant’s natural tendency to spread and grow,” Rita Wollmering, who grows hundreds of herbs at The Herb FARMacy in Salisbury, Massachusetts, says. “It allows for propagation of new plants with minimal disruption to the mother plant.” Layering also gives you a larger new plant than you might get from a rooted cutting, because the stem being rooted can be allowed to hold onto more leaves than it could support if it were severed from its parent. Best of all, you don’t need a greenhouse to expect close to 100 percent success with layering.
There are three main types of layering that you might do with herbs: simple layering, tip layering and mound layering. I’ll cover each of these in detail, and you can refer to the box to see which methods work best with your favorite herbs. But first, let’s cover the self-multiplying miracles your plants are capable of performing with only a little help from you.
From Stem to Root
In layering, you are asking a stem to stop being a stem, and instead develop roots, which many herbs are very willing to do. “When plants are wounded or cut, they have the unusual ability to take cells that are normally used for other functions, change them and start dividing them, and in the process change their destiny,” Dr. Stephen Garton, extension specialist in nursery and landscape horticulture at the University of Tennessee explains.
The most promising sites for these changes in plant destiny are the nodes — the places on the stem where leaves and little leaf buds are attached. Nodes are marvelous plant structures designed to do whatever they need to do to safeguard the life of the plant. They can produce leaves or sprout a new stem if the stem’s growing tip is removed, or they can grow roots should the plants become seriously threatened. “All the special cells that may be needed are laid down as the node develops, in positions where they can quickly respond when a change comes,” Garton says.
In layering, the change from stem to root often begins with a wound or injury to the stem. The plants then stage a three-step defense. They seal the wound, produce a callus that enables them to absorb more water, and then get busy growing new roots from the nodes. When we layer herbs, we are following this blueprint.
Fostering Fast Roots
Some stems need only a little encouragement to develop roots. In simple layering, you identify these stems, groom them in ways that tell the stems they need to produce roots and provide moist, root-friendly soil where you want the roots to grow. Simple layering can be done any time a plant is not producing flowers. This time of year, herbs that have already bloomed, been cut back and have since grown a flush of new stems are good candidates for simple layering. It’s a great method to use in the open garden or with herbs being grown in containers.
Back to our botany lesson. When plants are loading new nodes with cellular survival kits, they go extra heavy on low stems, in the nodes that are closest to the mother plant. In nature, these would be the last stems eaten by a hungry animal or lost through some other disaster. Identifying stems for simple layering means selecting two or three of these low, close-to-mama stems.
Next, shorten the selected stems to 4 to 5 inches by cutting off the tips. Then remove the leaves on the stem itself, leaving only a small tuft at the end, poodle-tail style. If the stem is brown and woody rather than green, use your fingernail to scratch the skin off of the bottom of the stem before burying it beneath at least an inch of soil. Allow the leaves at the end to rise out of the soil into light.
Now you can forget about your plant for at least a month, possibly longer. Much depends on the season, the species and the plant’s overall zest for life. With a hardy plant, such as creeping thyme, you can leave the layered plant out in the garden through winter. When the end of the layered stem shows noticeable new growth, cut it from the mother plant and transplant it where you want it to grow.
Tip layering is more forceful than simple layering, but again, it’s something plants know how to do. Instead of using low stems that are naturally inclined to root, you use long, leggy stems higher up on the plant. This time of year, look for stems that show a slight curve toward their tips, perhaps with noticeably smaller leaves at the tip ends. These are the best stems for tip layering. You can tip layer plants in the garden, or you can do it in multiple containers, setting the tips into containers set around the mother plant like a clutch of chicks.
Once you’ve selected your stems, figure out exactly where they will go if you bend them over and pin them into the ground so that a U-shaped section is buried 2 inches deep, with the tip emerging into light. Remove all of the leaves that will be in the buried section, then use a sharp knife to cut about one-third of the way through the stem at the point where it will be buried most deeply. Bury the stem, sprinkle on a little rooting powder if you like, and pin the stem into place with a 6-inch piece of wire or a bent paper clip, fashioned into a V.
Don’t worry if the stem almost breaks as you secure it into place; this is what you want to happen. The same way water backs up in a kinked hose, carbohydrates from the plant will accumulate in the wounded section, providing growing energy right where you want it. If you like, tie the end of the stem to an upright stake, such as a wooden chopstick, to make sure the stem stays acutely bent.
As with simple layering, how long the plant needs to grow roots varies with species, season and the plant’s natural inclinations. Strong creepers, such as Roman chamomile, will root in only two to three weeks. Vines are often very easy to tip layer, and they sometimes tip layer themselves when allowed to cascade to the ground. Herbs with woodier stems need more time. As a stem becomes woody, it accumulates a lot of strong support tissues. These require more time to make the transition from stem to root. Be patient.
Mound layering is a perfect match to the natural growth patterns of scented geraniums, Cuban oregano and many other herbs with stiff stems that are difficult to bend. This technique is best conducted in spring, when plants are beginning rapid new growth. Yet this is a good time to plan the project and to make plans for all the vigorous young plants you will have as a result.
For now, allow hardy plants to stay in the garden and keep tender ones in their containers. As new growth begins to emerge in early spring, lop off the plants’ heads about 2 inches above the surface. When shoots (called stools) pop out around the base of the plant, cover them to half their height with a half-and-half mixture of sand and peat moss (or any light-textured potting soil). Every week, add another layer of soil so that it forms a mound over the base of the plant. When the mound is 3 inches high and the stools are showing steady growth (usually 4 to 6 weeks after you started), use your fingers to see if the base of the stools is hairy with roots. If so, gently dig up the mother plant (or shake it out of its pot) and use a sharp knife to cut each baby away, keeping as many roots intact as you can. Replant them right away, and provide shade if needed to give the fledglings time to adjust to life on their own.
Mound layering usually does mean saying goodbye to the mother plant, but it’s a small loss when you have a half dozen offspring to show for your efforts. Simple and tip layering leave the mother plant intact. With many herbs, you can choose whichever method seems most suitable.
Don’t be afraid to try. For many of us, propagating our herbs is as much an exercise in sentimentality as it is in plant preservation. Keeping the exact strain of rosemary given to us by a loved one or preserving the life of a terrific tarragon that has pleased our palates for years provides the motive for layering, which is easy, practical and fun.
Tips for Low-Risk Layering
Barbara Pleasant lives in the mountains of western North Carolina where she enjoys gardening, garden writing and cooking. She has received many book awards including a Garden Globe Award from the Garden Writers of America for Garden Stone (Storey, 2002).