Photo by Lee Reich
Totiotence refers to the potential ability of any part of a plant — except reproductive cells (egg and sperm) within a flower — to give rise to any other part of a plant, or even to a whole new plant. That’s because all of a plant’s cells (with some exceptions) house identical genetic information. Depending on the cellular environment and other influences, a cell may become a root, a petal, or any part of a plant.
I’ve made plenty of use of totipotence to multiply a favorite houseplant or shrub, sometimes doing nothing more than dropping some fantail willow stems into a glass of water and waiting for roots and shoots to sprout. Such asexual propagation, so-named because it bypasses using seeds (except in the case of apomictic seeds, such as those borne by citrus), results in new plants that are genetically identical to each other and to the mother plant. Totipotence lets gardeners start whole new plants from pieces of stems, roots, leaves, or even just a few cells from the growing tip of the mother plant.
Starting from Stems
Putting the base of a stem into a suitable environment induces roots to form. Water, although effective with some easy-to-root plants, such as coleus and willow, isn’t actually a good rooting environment. Roots need to breathe; if they’re submerged in water, they’ll soon be gasping for air. Shaking or changing the water occasionally helps. Roots that do develop in water are structurally different from those that develop in soil, and sometimes have difficulty making the transition from water to soil.
The most effective rooting environment holds moisture and air, and provides support. Nutrients are unnecessary at this point, because the stem draws on its nutrient reserves to grow roots and new shoots, and, anyway, the rootless stem would have a hard time drawing up nutrients. Any ordinary potting soil, with a little extra perlite added for better aeration, is suitable. I make up my own rooting mix by combining equal parts peat moss and perlite.
Photo by Lee Reich
Softwood stem cuttings are pieces of stem, typically 6 inches or so in length, with leaves attached. These cuttings generally root quickly, but need care to keep their leaves from drying out before roots develop and can draw in more water to support them. I slow water loss from my softwood cuttings by reducing the size or number of leaves, or by increasing humidity around the leaves. A covering of clear plastic or glass works well for this. So does an intermittent mister or, even better, an artificial leaf that actuates a mister when it gets dry, which is ideally about the same time that the real leaves dry out.
Softwood cuttings don’t have a lot of energy reserves and need light so that their leaves can feed them. I site my softwood cuttings in bright, indirect light, and keep them humid beneath a tent or inverted jar.
Hardwood stem cuttings are lengths of stem — usually only a season old — clipped from dormant, leafless (if deciduous) trees, shrubs, and vines. Hardwood cuttings are less susceptible to drying out than softwood cuttings, and, if leafless, don’t need light—at least until they sprout leaves. Since the presence of leaves can promote rooting, I sometimes take hardwood cuttings in fall, while the stems still retain one or two leaves. The age of the leaves, cool weather, and lower sunlight reduce water loss for these cuttings.
The procedure for rooting hardwood stems is essentially the same as rooting softwood cuttings, with two wrinkles. First, there’s no need to cover deciduous cuttings to increase humidity; they can even be rooted outdoors in any well-drained soil. Second, cold-hardy woody plants need to experience a certain amount of cool weather before they can grow new shoots. Cuttings taken in autumn and rooted outdoors, as well as cuttings taken at the end of winter, will experience this cool period naturally.
With stem cuttings, you start with stems and induce them to sprout roots. The opposite is true with root cuttings: You start with roots and coax them to grow stems. Not all plants can be propagated by root cuttings; those that can include oriental poppy, lilac, raspberry, bleeding heart, phlox, and herbaceous peony.
Ideal root pieces are 2 to 3 inches long and the thickness of a pencil. The best time to dig them is when the plants are dormant, generally in late winter. In the case of oriental poppy and bleeding heart, the best time to dig for roots is summer, right after the plants finish flowering and go dormant. Small, delicate root cuttings can be scattered on rooting media, and then covered with another inch of media. Plant fatter root cuttings vertically in rooting mix, with the ends that were closest to their stems pointing up and just beneath the surface of the mix.
Leave it to the Leaves
Even leaves can be made to grow roots and shoots. African violet, sansevieria (snake plant), begonia, and jade plant are among those most amenable to multiplication via leaf cuttings. This can be done in several ways. With rex begonias, laying a leaf flat on moist rooting media and scoring across some of the main veins with a razor gives rise to new plants at each cut. With other begonias and African violets, all that’s needed is to poke their leaf stalks, or triangular cut portions of leaves, vertically into a rooting media. A tent of plastic film or an overturned clear jar maintains the needed high humidity until new plantlets appear.
Photo by Lee Reich
To avoid the threat of rot, let leaf cuttings of succulent plants dry out and heal for a couple of days before poking them into moist rooting media, and then let the media thoroughly dry out between waterings. Chop long, fleshy sansevieria leaves into 2-inch lengths, and then poke their bottom halves into rooting media. When using leaves from jade plants, leave them whole rather than chopping them up. Kalanchoe have the easiest leaves to root; they naturally develop plantlets around the edges of their leaves that often drop off and root all by themselves. Succulents shouldn’t be kept under cover for increased humidity, or they’re apt to rot rather than root.
When it comes to grafting, there’s no need to coax stems to make roots; you simply join a scion (a piece of stem) atop the rootstock (the stem of an already rooted, growing plant). The rootstock might be either a very young or a mature plant. All new growth above the graft will be from, and genetically identical to, the scion. I’ve used grafting to make, or make over, many of my fruit trees. You can make a new, young pear tree, add another variety to an existing pear tree, or decapitate an old pear tree and change it to a better variety. Similarly, you can graft a pink dogwood stem onto a white dogwood tree to create a multicolored flowering dogwood.
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The rootstock itself might serve some purpose other than merely providing roots. It can influence the form of a plant. Weeping cherry growing on its own roots merely creeps along the ground; grafting it high on an upright trunk of a non-weeping cherry rootstock brings the weeping head off the ground. A rootstock can influence the eventual size of a plant, as attested to by my 10-year-old ‘Liberty’ apple tree, topping out at only 8 feet thanks to the ‘M27’ dwarf rootstock on which it’s grafted. The appropriate rootstock can promote quicker bearing, or tolerance to soils that are too wet, too dry, or too salty.
How is it possible to lop the top off a growing plant, remove the stem from another plant, stick the latter atop the former, and have them knit together and grow? When a stem is cut, a necrotic plate of dried and crushed cells at the cut secretes waxy substances to seal the stem off from water loss and pathogen attack. The plant begins to grow parenchyma cells, which are thin-walled cells plump with water. These cells form a callus, which is an undifferentiated mass of cells that eventually breaks through the necrotic plate. As callus of rootstock and scion intermingle, the bond provides some mechanical strength to the graft, and even some water flow and nutrients between rootstock and scion.
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But for long-term flow of nutrients and water between rootstock and scion, we need to look near a stem’s cambial layer, which is where new cells form. The outer part of this layer produces new phloem cells, through which sugars and other metabolic products “phloe” downward in stems. From the inner part, new xylem cells (upward conduits for water and minerals) originate. Eventually, if the cambial layers of rootstock and scion are sufficiently close, xylem and phloem cells of the rootstock “find” those of the scion, and functional plumbing is established between root, stems, and leaves of the newly made tree.
No graft will survive without some mechanical strength to keep rootstock and scion together. That strength usually comes from fibers, which are a type of xylem cell. The dwarfing ‘M9’ rootstock has very short xylem fibers, which provide insufficient mechanical strength to keep a heavily bearing tree from toppling. Mechanical strength of grafts with ‘M9’ rootstocks come from the stakes needed to support these trees throughout their lives.
Photo by Getty Images/AnastasiiaM
Kinship, contact, and hydration are key to a successful graft. The rootstock and scion must be closely related—usually the same genus and species. Apricot, for instance, can be grafted onto peach, since they’re both members of the Prunus genus. Cambiums of stock and scion need to be sufficiently close, if not aligned. Avoid allowing the cut surfaces to dry out; this is easily accomplished with a coating of Tree-Kote® or with a wrap of Parafilm®. Other products are also available for this purpose.
Grafting for All Reasons
Given the few prerequisites for a successful graft, and grafting’s long history (dating back to 1000 B.C. in China), it’s no wonder there are many ways to join scions to rootstocks. Described below are three easy grafts I’ve used. The ideal time for these grafts is in spring, just as plants are awakening. Scions are best cut ahead of time so that they’re still dormant when grafted. Cut the scions — pencil-thick, 1-year-old stems — in late fall or winter, put them in a plastic bag, wrap the bag in a moist paper towel, and then put it all inside another plastic bag, well-sealed, in a refrigerator or cooler.
Photo by Lee Reich
Whip grafts are my choice when rootstock and scion are about the same thickness (pencil-thick). Cut off the bottom of the scion with a smooth, 1 to 1-1/2-inch-long sloping cut, and then make a similar cut at the top of the rootstock. Hold the sloping cuts against each other; align just one edge of each if their diameters don’t exactly match. Then, bind rootstock and scion together with a rubber grafting strip or thick rubber bands, sliced open. Next, seal in moisture by covering the cut surfaces; I recommend Parafilm®. Once a graft is growing strongly, cut a vertical slit into the binding to prevent it from choking the plant.
Photo by Lee Reich
Cleft grafts work well when the rootstock is much thicker than the scion, up to about 2 inches thick. At the base of each scion, make two bevel cuts less than halfway through the scion, each 2 inches long and not exactly on opposite sides, so that, viewed head on and from below, the uncut portion is slightly wedge-shaped. Turning to the rootstock, lop it off squarely with a saw, and then create a split a couple of inches deep in the middle of the cut surface by hammering a heavy, sharp knife right down into it. After removing the knife, push a screwdriver down into the split to separate it enough to insert the two prepared scions at each edge of the cleft with their cambiums aligned with the cambium of the rootstock. Pulling out the screwdriver causes the springiness of the rootstock to close the cleft and hold the scions securely in place. Thoroughly coat all cut surfaces to seal in moisture.
Photo by Lee Reich
Bark grafts are called for with larger rootstocks, up to many inches in diameter. This graft comes with an especially good insurance policy, because you can stick three or more scions onto each rootstock. Only one scion needs to grow, but the more that are grafted, the greater the chance of success. Prepare a scion for a bark graft with a bevel cut 2 inches long, at its base, not quite all the way across from one side to the other. On the opposite side of the cut, nick off a short bevel. Then, into the freshly cut stub on the rootstock, make two vertical slits through the bark, each about 2 inches long and as far apart as the width of the base of the scion. Carefully peeling back the flap of bark welcomes in the long, cut surface of the scion, putting the cambial layers of rootstock and scion in close contact. Repeat this process with the other scions, all around the stub. With the peeled back flaps of bark from the rootstock pushed back up against each inserted scion, hold everything in place with one or two staples from a staple gun, or by tightly wrapping the join with stretchy electrician’s tape. Finally, everything needs to be sealed to prevent moisture loss
Don’t turn your back on any completed graft and expect success. I check my grafts the following day and reapply sealant as needed. The year after a cleft or bark graft, I reduce “takes” to the single most vigorously growing scion.
Auxins are plant hormones that play an important role in rooting cuttings. If you apply auxins directly to the base of a cutting, there’s a greater chance the cutting will take root, and rooting might be hurried along. Before synthetic auxins became available, savvy gardeners would help rooting along by soaking cuttings in the water in which the stems of willow, an extremely easy-to-root plant, had previously been soaked. It worked! The problem is that natural auxins decompose too quickly to be of practical use after they’ve been extracted from a plant. That’s where synthetic commercial auxins — such as α-naphthalene acetic acid (NAA) and Indole-3-butyric acid (IBA) — come into play.
Synthetic rooting hormones are available either in liquid or powder form. Concentrations and combinations of auxins vary by manufacturer, with higher auxin concentrations generally used for more difficult-to-root species. Fungicides may be added to prevent cuttings from rotting. Apply powders by dipping the base of a cutting into the powder, gently tapping to shake off excess, and then sliding the cutting into a hole dibbled in the rooting mix. Varying amounts of powder might cling to a cutting, leading to inconsistent results. Liquid formulations, besides being more consistent, are more rapidly absorbed by the roots. Merely soak bases of cuttings in the liquid according to the time required by the specific hormone concentration you’re using.
Rooting hormones aren’t essential in propagation, nor do they perform magic. Don’t use them for propagating easy-to-root plants, such as willows and chrysanthemums, or for plants that won’t root from conventional cuttings, such as mature apple or maple trees. Rooting hormones also won’t make up for poor propagation practices.
Lee Reich turned to writing, lecturing, and consulting after years of plant and soil research with the U.S. Department of Agriculture and Cornell University. He holds a doctorate in horticulture and is the author of many gardening books. This is an excerpt from his latest book, The Ever Curious Gardener.