Plant Propagation Simplmea

In former days many home gardeners found it difficult to increase the supply of their favorite evergreens by the usual methods of reproduction, viz., seeds, layers, and cuttings. The complexity of starting new plants has been materially lessened since the introduction of polyethylene plastic. In the field of plant propagation its use has been a real boon. No longer is a greenhouse a necessary possession for raising these plants from seeds and cuttings. Polyethylene is a substance which has the ability to retain mois­ture and to permit an exchange of gases. Because of these qualities the humid, even temperature of a greenhouse can be provided in your own house by improvising a miniature propagating unit. This is done by merely covering a pot or a garden flat with polyethylene film supported over a wire frame, or held in position by plant stakes placed in each corner of the flat; the plastic may either be tied down at the base with string or folded under the container. In the case of a small pot, the plastic can be held in place with a rubber band. No care of any kind will be required for weeks at a time, however, it is advisable to check periodically in order to make sure the moisture content is sufficient.

There are two fundamental methods of propagation: the sexual method, whereby plants are increased by means of seed; and the asexual (vegetative) method. The sexual method is not always reliable, because seedlings can­not be depended on to run true to type, and in most instances is a slow tedious procedure. The principal reason to recommend it is because you never know when a new strain of plant may result. The most reliable way to perpetuate a plant true to type is by vegetative reproduction. With this method, plants are propagated by cuttings, layers, division, grafting, and budding.

SEEDING

Generally speaking, the seeds of cone-bearing evergreens are collected at the time the cone scales open; at that time the coat will turn brown and the seeds themselves will become firm. The seeds must be well cleaned before they are placed in storage; those with wings should have the wings removed. To obtain seeds from fleshy fruits (such as the berries of Holly) mash the fruits and soak them in water for three or four days. During this soaking period stir them vigorously several times; this will hasten the sepa­ration of the pulp from the seeds. Care must be taken not to allow them to "sour." The viable seeds will settle in the bottom of the container, and those that are nonviable, together with the pulp, will collect on the sur­face and should be discarded. The good seeds must be thoroughly washed again with water before they are stored. A better way to separate the pulp from the seed is to soak the fruits in ethyl alcohol for a few minutes.

One must be on the alert to harvest seeds from Rhododendron, Laurel, Azalea—and any other species which produce fine seeds—just as soon as the pods or capsules turn brown and commence to open. Otherwise, a year's harvest may be lost as they will be dispersed by that ardent propa­gator—Mother Nature. Seeds of this type are stored in paper bags and kept in a cool room. They are either sown outdoors in spring or started indoors during the winter. If they are to be kept longer than a few months, it will be necessary to store them in tightly covered jars and to place them in the refrigerator.

Most of the conifers, such as Pines, Spruces, Firs, and Junipers, as well as many other types of plants, have seeds with a hard outer covering; these seeds are softened to assist germination. This is done by sowing them in flats between layers of moist peat moss, shredded sphagnum moss, or sand. The flats are then stored during the winter in a cold temperature, but above freezing. This process is known as stratification. In modern homes, with their warm basements, it is sometimes difficult to find a suitable place in which to store these seeds. Again polyethylene plastic has proved its worth in simplifying this step in raising woody ornamentals from seed. The seeds are mixed with moist (not wet) peat moss and placed in plastic freezer bags. Label the bags, tie them securely with string or seal them, and store them in the refrigerator. A temperature range of 34 to 40° F. will usually answer the purpose. Subjecting seeds of this type to this treatment for sev­eral months will also hasten the after-ripening period which is necessary for maturing the embryo; germination does not take place until this matur­ing process within the seed has been completed. The time required for its completion varies with the different evergreens. Ordinarily seeds gathered in the fall and kept in the refrigerator until spring can be sown outdoors at that season. During the course of the winter examine the seeds from time to time, and if any show signs of sprouting remove them from the refrigerator and sow them in flats or pots. Keep them indoors until the weather has become mild enough to plant them outdoors, this will be at the time that annual seedlings are set out.

The use of sphagnum moss in propagation is invaluable. It is exception­ally clean, making sterilization unnecessary. Sphagnum moss can be pur­chased in a finely shredded form and ready for use at most garden supply stores, or the moss can be shredded by working it by hand through a screen which has three meshes to the inch. It should always be shredded for seeds or for cuttings. Before using it for any purpose it must be thoroughly watered and drained. This moss is highly retentive of moisture; furthermore, its fine texture in the shredded form qualifies it as a medium for sowing fine seeds; these will fall between the tiny particles of moss and will require no more covering. Larger seeds should be covered with additional moss. Although sphagnum is acid, nevertheless it can be used for starting plants that require alkalinity.

Sphagnum moss is exceedingly low in nutrient value, therefore plants grown in it for any length of time should be fed with a special fertilizer used in a liquid form according to the manufacturer's directions.

For propagating purposes, containers can either be entirely filled with sphagnum, or this moss may be used as a finishing layer over a bottom layer of soil, in which case allow space for at least 1 inch of sphagnum compressed to an even surface. The finished layer should come to within ½ to 1 inch of the top of the container. The advantage of a layer of soil under the moss is that the transplanting can be deferred for a longer time; the young plants will strike root in the earth and thus be supplied with sufficient nutrients to maintain growth. Whether a flat or a pot is used, to assure proper drainage be sure not to overlook placing broken pieces of pots concave side down, over the holes in the bottom of the container.

Seeds that have been kept in the refrigerator over the winter are sown outdoors in spring in a well-prepared seed bed. In selecting the location for the bed, choose well-drained, level ground that is in a protected place. A light, friable soil, and one that is well worked and free from stones, roots, or soil clods is best for the purpose; rake the surface into a well-pulverized tilth. Fine seeds are merely sprinkled over the surface of the bed and pressed gently into the soil; the larger seeds are covered to a depth of twice their diameter. The seed bed must be kept shaded and moist until sprouting occurs. When the young plants are 4 or 5 inches high they are transplanted to a well-prepared bed and set out about 3 inches apart in a row, the rows are approximately 8 inches apart. The seedlings are very delicate, and if they are to survive, every care must be given them. Plants that require acidity will grow better if an ample supply of peat moss or oak leaf mold is worked into the earth. In transferring the seedlings from the seed bed to the transplanting bed, every precaution should be taken to prevent the roots from drying out; keep them damp by placing them in wet newspaper and away from extreme heat. After the young plants have been moved to their new quarters, they must be watered regularly and shaded for the first week or so. Later transplantings will depend entirely on the size of the plants; they should never be allowed to become overcrowded. Evergreens that grow rapidly will probably have to be moved in a year; whereas the slower growers may not require to be transplanted for two years.

CUTTINGS

Vegetative propagation has been greatly facilitated by the use of poly­ethylene plastic. Because of it, excellent results have been obtained in reproducing evergreens by means of cuttings, air-layers, grafting, and bud­ding. The plastic is not required in simple layering.
When plants are increased from cuttings, the preparation of the propa­gating unit is identical in every respect to that described under seeding. Among the evergreens that are successfully grown from slips are Arbor-vitae, evergreen Azaleas, evergreen Barberry, Box, Cotoneaster, Euonymus, Pyracantha, Gardenia, Mahonia, Osmanthus, Pieris, evergreen Privet, Holly, Rhododendron, creeping Junipers, and Yews. Ground covers such as English Ivy, Pachysandra, Sarcococca hookeriana humilis, Skimmia japonica, Pachistima canbyi, and Vinca minor can all be rooted easily by cuttings.

The best season for making cuttings is usually in summer after the new growth has passed its wilty, succulent stage, however, the time varies with the different species. In many instances the slips are taken in autumn and into midwinter, provided the wood is not frozen. The writer has had good results with cuttings made from the tips of the shoots from broad-leaved evergreens taken in spring, as well as from those that have been broken in late winter snowstorms; it is well worth-while to try your luck at salvaging these for increasing your stock. The cuttings made in winter were planted in bulb pans or pots filled with sphagnum moss, covered with plastic, and kept indoors on a window sill with a northern exposure.

Cuttings are made 3 or 4 inches long; a clean cut is made directly below a node (joint). The lower leaves are removed but the upper ones are re­tained. If the leaves are large, like those of Japanese Aucuba, they will not be as likely to wilt if they are cut in half. To facilitate the formation of roots, the ends of the cuttings are dusted lightly with a hormone rooting powder; the slips are then pressed firmly into the rooting medium and watered. The receptacle is covered with plastic, and no further care will be required for weeks. It is decidedly advantageous to use a clean (so called sterile) rooting medium, for this purpose shredded sphagnum moss, styrofoam, perlite, and vermiculite (sold under various trade names) are all satisfac­tory choices to make. Peat moss and sand or sand alone are also most sat­isfactory for rooting purposes.

Various conifers may be grown from cuttings made from the new growth when it has become mature, which is late in summer. Sometimes cuttings are made before the growth starts in spring, also in the autumn and dur­ing the winter; it is not advisable to make slips after the spring growth has started or in the early part of the summer. Percentage-wise different coni­fers root better if the cuttings are made at the specific time that particularly suits the individual plant, for example, the Colorado Fir grows best from cuttings made the latter part of the winter, whereas the Red Cedar strikes root more readily from cuttings made in December. The best time to take cuttings of Colorado Spruce is the latter part of the winter, while cuttings of the Norway Spruce respond better when taken from the late fall to March first.

Among the conifers that root more easily are the creeping Junipers, American Arbor-vitae, and False-Cypress; Pines are usually difficult to root.

A device for rooting cuttings by using fluorescent lights is another inter­esting means of propagation. There are devices on the market for propa­gating plants by this means. The procedure is a simple one; the cuttings are inserted in flats filled with one of the recommended rooting mediums and well watered. The flats are placed in the propagator; the fluorescent lights which are in the lid are then turned on and the lid is closed. The unit is kept in the house at a room temperature of 70 to 75° F. (no lower than 50° F.). If the room temperature runs up to 80° F., then the unit will have to be carefully watched, and the lid may have to be opened from time to time. The slips should root in a few weeks provided the conditions are favorable.

Another way to root cuttings is by the mist method. Jewel W. Templeton, who helped develop this method of propagation, describes it as follows: "The principle of mist propagation is very simple: Just keep all of the leaves on the cuttings wet all the time—nothing more. Obviously, you keep the leaves wet in order to keep the leaf tissue from drying out, and that seems to be all that is necessary—granting, of course, that you have the cuttings in an otherwise thoroughly favorable environment.

"Naturally, cuttings must be kept in light if they are to live and root. When light falls on the leaf of the cutting, it gives off heat which makes the leaf warmer. Thus the leaf soon becomes warmer than the surrounding air. Water evaporates faster from a warm object; so a warm leaf tends to dry out faster. Also, the warmer a cutting is kept, the more physiologically active it is, so that it tends to transpire even more moisture.

"Cuttings are usually shaded when they are rooted in the greenhouse or cold frame in order to protect the leaves from strong light that would change into heat and make the leaves too hot. But cuttings need light if they are to stay healthy, and the amount of shade required to keep the cuttings cool enough is often so great that the cuttings do not receive enough light to enable them to manufacture the food they need to remain healthy. There­fore, the use of shade to keep cuttings cool is not always a completely satisfactory solution.

"Under mist, in practice, even with the constant addition of a large amount of heat from strong light, the leaves stay a few degrees cooler than the surrounding air. This slight difference in temperature is more impor­tant than it would at first seem to be. It means that water will not want, so to speak, to evaporate from the leaf tissue. This means that by using mist, cuttings (even very soft tender new shoots) can be kept much warmer than usual without causing undue loss of water from the leaf tissues. Under these conditions cuttings can be presumed to be much more active physio­logically, and therefore can be expected to root faster.

The Mistic Bubble. (Courtesy, Mist Methods Company.)

"These two facts, along with technological advances that have made available a large assortment of equipment—such as fog nozzles, plastic enclosures, time controls, electronic controls, solenoid valves, etc.—give the propagator much more latitude in supplying favorable rooting conditions than he has had in the past. He can give the cuttings all the light they need, and he can keep them turgid at a much higher temperature than before. He can also choose a much greater variety of plant material for rooting vegetatively, since even succulent perennials and the tender shoots of house plants remain perfectly turgid under a properly constructed mist propagation unit.

"Cuttings to be rooted under mist should be taken during the growing season and should be from new growth. To root successfully under mist, every cutting must have leaves—about as many as the plant naturally has. If this produces crowding, half of each leaf may be cropped. The leaves should be stripped off for about an inch from the end to be stuck into the rooting medium. Cuttings may be taken with scissors, clippers, a knife, or just pinched off with thumb and finger. It is not necessary to cut to a node or joint; and from long sections several cuttings can be made. Each cutting should be from 2 to 5 inches long. Larger ones will root but do little better and take up too much space in the bed.

"With some plants exact stage of growth is important for successful rooting under mist. In general, most deciduous shrubs, succulent perennials, and house plants root best from very tender new shoots. However, woody ever­greens, for the most part, root best from fairly mature shoots on which the leaves are nearly mature and have changed, or have begun to change, to a darker green color. Most broad-leaved evergreens root well during the warm months and, therefore, are adapted to outdoor mist propagation even in the northern sections of the country. In the case of the narrow-leaved evergreens the situation is slightly different; they root better during the colder months from slightly more mature cuttings than the broad-leaved evergreens. Therefore, mist can be used in unheated enclosures, or out­doors, all over the country for most shrubs, house plants, perennials, and broad-leaved evergreens; but in cold sections, if mist is to be used on narrow-leaved evergreens (such as arborvitae and pfitzer), provisions must be made to prevent the water from freezing. This, of course, would make an outdoor mist system for this particular group of plants impractical in the colder parts of the country. However, mist is being used in many greenhouses.

"Treatment with plant hormones is helpful in rooting some difficult varie­ties of plants. However, nearly every plant which can be rooted at all will root to some extent without hormones. Each plant variety has its own hor­mone requirement and tolerance, and many plants can be permanently damaged by the use of too strong a hormone. The manufacturers of most hormone preparations supply tables for their particular hormones with the recommended treatment for each plant variety.

"Mist Methods Co., Winchester, Tenn., makes a small mist propagation outfit called a Mistic Bubble, which comes complete, except for bricks and sand, and Can be set up on any level spot on a lawn or in a garden either in full sun or in partial shade. The bricks covered with Fiberglas screen furnish perfect drainage. Coarse sharp sand is used as a rooting medium. Mist is supplied through a low-capacity (1 ½ gallons per hour) stainless steel nozzle which is very economical to operate. An ordinary garden hose from the house water supply is screwed on the nozzle supply pipe. The Mistic Bubble comes with complete operating instructions and requires no particular experience or knowledge for excellent results. A wide variety of plants have been successfully rooted with it; some of these had been diffi­cult or impossible under other than mist methods. Among plants successfully rooted are the following:
Abelia Laurus nobilis
Äucuba Ligustrum
Azalea Mahonia
Berberis Osmanthus
Buxus Pachysandra
Camellia Pieris
Elaeagnus Pyracantha
Euonymus Rhododendron
Hedera helix Thuja
Ilex Viburnum
Juniperus Vinca

"The Mistic Bubble can be operated all year in the southern parts of the country, and whenever the temperature is above freezing in other sections."

LAYERING

Layering is the process by which a plant can be propagated by rooting a branch while it is still attached to the parent plant. In nature examples of natural layering are frequently found in shady or wooded locations, where year after year the falling leaves are left undisturbed. The procum­bent branches sometimes take root in the damp accumulation of leaf mold which results from the decomposition of leaves. This is known as natural layering, and it occurs frequently among members of the Heath Family (Ericaceae). This group of plants includes such favorites as Rhododendron, Azalea, Mountain Laurel, Andromeda, and Leucothoe.

Simple Layering

Simple layering differs from natural layering in that the home gardener follows nature's example and supplies the layer with the conditions neces­sary to encourage the formation of roots. This is one of the best methods for the novice to practice. The plants that are adapted to this kind of propagation are those with low-swung branches that can easily be pegged down to the ground. The best time to do simple layering is in early spring before growth has started, using the previous season's growth, or late in summer when the wood has matured from the growth made during the current season and before the wood is in a hardened condition.

The ground should be well prepared for the layer: peat moss or leaf mold with sand well incorporated in the soil will provide suitable growing con­ditions. The branch is then wounded, the position of the cut being determined by the size of the shoot; generally it is made a foot or so below the tip of the branch. The wound is made either by scraping the bark down to the wood with a sharp knife, or by making a slanting cut 1 or 2 inches long down the branch where the roots are to develop. This cut is usually made halfway through the branch; at any rate, the incision should be deep enough to make it possible to apply some hormone rooting powder lightly to the cut surfaces. The cut is kept propped open with a small amount of moist sphagnum moss. It is best to make the cut on the upper rather than on the lower surface of the branch, as there will then be less danger of breakage. The wounded part of the branch is given a twist so that its top will stand in an upright position; it is then anchored to the mellow soil and held in place with pieces of heavy wire that are U-shaped, or with branches that are forked. Some of the soil mixture is next firmed over the wound to a depth of about 3 inches. The branch is supported in its ver­tical position with a stake or a stone; the upper part of the branch should be left uncovered so that the plant can continue to function normally. The layer should not be allowed to dry out at any time. Since it draws its sus­tenance from the parent plant, no feeding is necessary. When the new layer has grown a good root system of its own, it can be severed from the mother plant and lifted with a ball of earth around the roots, which will lessen the shock of transplanting and make it more likely to succeed. By spraying the newly rooted plant with Wilt-Pruf before it is detached from the mother plant the danger of loss will be further reduced. Set out the new plant in a shady place with plenty of peat moss around the roots; it should be kept watered and the leaves sprinkled until growth begins, which will indicate that it has become established. The length of time re­quired for an adequate root system to develop varies considerably; fre­quently it takes evergreens from 2 to 3 years before they are ready to be severed from the parent plant.

Air-Layering

Although there are various methods used in layering plants, simple layering and air-layering are the easiest kinds to employ with certain ever­greens. Some conifers can be air-layered, but it is difficult to induce their root formation; consequently, for this particular group of plants simple layering is preferable to air-layering, provided the branches are sufficiently procumbent to make this method feasible.

Air-layering has been practiced by the Chinese for centuries, and since the introduction of polyethylene plastic it has become possible to use this ancient practice outdoors in most climates; formerly this type of propaga­tion was restricted to greenhouses and tropical climates, where root develop­ment is encouraged by atmospheric conditions. In air-layering a welldeveloped branch that is one or more years old is chosen for the layer; young growth emits roots more readily than older wood. Naturally avoid selecting a branch for this purpose that should be left untouched to pre­serve the proper shape of the plant. The leaves and twigs should be cut off from the section of the branch to be layered. As in simple layering, a slanting cut 1 or 2 inches long down the branch is made as described in simple layering, and the cut surfaces should be lightly dusted with hormone rooting powder; the bark is left intact. The cut is held open with a small amount of moist sphagnum moss as in simple layering. Another method is to cut away a ring of bark about ½ to 1 inch wide around the branch, and use the rooting powder as previously mentioned. In each case the cut should be made just below a node (joint). The next step is to moisten some sphagnum moss, squeeze out any surplus water, and envelop the layer with a big handful of this excellent rooting medium; be careful to use it moist but not wet. This ball of sphagnum is then completely covered with an 8 x 10 inch sheet of plastic, both ends of which are twisted and tied firmly with Twist-ems, waterproof electrician's tape, or florist's plant tape. The plastic should be wrapped so that the overlap will be on the underside of the branch to keep out the rain water.

Air-layers are made in the spring before the buds start to open, or in the late summer or autumn, since cool weather is more conducive to root for­mation. The time it takes for the roots to develop varies from a few weeks to a year or more, depending on the kind of plant to be layered and the age of the branch.

The roots do not always show through the plastic, and if they do not ap­pear in 2 or 3 months it is advisable to open the covering and examine them, because when the roots have formed the time will have arrived to sever the new plant from its parent. However, when roots appear late in the fall, the layer may remain attached to the mother plant until the follow­ing spring; the warm, genial weather will encourage more rapid growth. The layer should be separated from the parent plant at the base of the ball of sphagnum, allowing some of the moss to remain on it in order to disturb the roots as little as possible. If the new plant is sprayed with Wilt-Pruf before it is detached (as recommended under simple layering), the danger of transplanting will be lessened. The planting and care of the young plant in its new quarters are the same as in simple layering.

DIVISION

Certain kinds of evergreens can be multiplied by division; these include Laurel, Leucothoe catesbaei, Ledum, and various ground covers, such as Peri­winkle, English Ivy, Pachistima canbyi, and Sarcococca hookeriana humilis. Ordinarily plants that develop many branches from the ground up lend themselves to this form of propagation. A sharp spade is used to cut a clump into two or more parts, each division should have a sufficient part of the root system left intact to sustain its growth. Before planting, prune back all straggly roots and shorten the branches to encourage a stocky growth.

GRAFTING AND BUDDING

When plants are difficult to reproduce from seeds, cuttings, layers, or division, then grafting (including budding) is often practiced. In common with the other vegetative methods of propagation, the resulting plants are sure to come true to type. Conifers are frequently increased by this means. By using this technique a scion or a bud is taken from the strain you desire to perpetuate, and is inserted on another plant in a cut made for the pur­pose. The plant on which the graft is made is called the stock, rootstock, or understock. The scion used for grafting is a piece of twig with one or more dormant buds attached. In the process known as budding (another form of grafting), either a single dormant bud, or a bud with a sliver of bark attached, is used for grafting on to the understock. In most cases the understock and the scion or bud used for the graft should be closely re­lated, otherwise success is more difficult to achieve. The growing part of the mature stem of a woody plant is called the cambium layer; this is be­tween the bark and the wood. In making the graft it is imperative to place the cambium layer of the scion or the bud in direct contact with the cam­bium layer of the understock, otherwise the union will fail. The scion or bud is securely tied to the understock with soft string, raffia, or a rubber band. Formerly when the grafting operation was completed, the union was then covered with grafting wax, whereas nowadays the wax can be replaced with a Plastic Plant Wigwam made of polyethylene plastic, which was invented by Victor J. McNitt of Sherburne, N. Y. This film greatly simplifies the procedure and makes it possible for the amateur to launch into this method of propagation which previously was generally practiced only by experienced gardeners.

Those who are interested as to the technique of grafting will find infor­mation in Plants and Gardens "Handbook on Propagation" (1957), Brooklyn Botanic Garden, Brooklyn, N. Y.

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