Propagation
Increasing plants is one of the most interesting and rewarding aspects of gardening. Nature’s usual method is by means of seed, but in many instances, cultivated plants do not come true from seed, therefore to perpetuate particularly desirable plants, it may be necessary and quicker, to propagate vegetatively, that is by division, suckers, cuttings, layering (including aerial layering) and budding.
For details of propagation by seed see Seed sowing.
Division
This is a simple method of increasing plants, particularly hardy perennials with fibrous roots, such as Michaelmas daisies, solidagos, heleniurns, which should be done in autumn, when the plants are dormant, or in spring when just starting into growth. Established clumps are lifted with the aid of a fork and divided into several pieces—an old knife is useful for this purpose, although where the clumps are large and tough it may be necessary to use two border forks, plunging them into the clump back to back and then working them backward and forwards until the clump falls to pieces. Old pieces of the woody root should be discarded and only vigorous well-rooted pieces retained. The same applies to certain shrubs including some of the berberis, spiraeas, pernettyas and others that produce a number of stems, rather than a single main growth. Rock garden plants, such as aubrietas, alpine phloxes, some of the campanulas and mimulus, may also be carefully divided and replanted.
The rhizomatous roots of the tall bearded, or flag irises should be lifted and divided soon after flowering; July is considered the best month for this work. Replant healthy, strong pieces only, and at the same time cut back the sword-like leaves to within about 1520cm (6-8in) of the root. When replanting, the rhizome should be on the surface and not buried, making the roots firm in the soil.
Certain orchids, such as cymbidiums, cattleyas and miltonias may also be increased by careful division. This is a major operation in a plant’s life and naturally, some care and attention are necessary so far as watering and shading are concerned, until they have developed a good new root system to sustain themselves.
Suckers
These are shoots of underground origin which may often be removed from the parent plant, with the aid of a sharp knife, complete with roots. This provides a ready means of increase; on the other hand certain plants, such as some poplars, plums, almonds and rhus (sumachs) are liable to send up suckers over quite a wide area which can prove a nuisance. The usual time to remove suckers for propagation purposes is in autumn or spring. Lilacs on their own roots may be increased in this way, also raspberry canes, pernettyas, bamboos, amelanchiers and some rose species, among others.
Cuttings
There are various different types of cuttings which are widely used for propagation purposes. The parts of a plant used may consist of young, green stem-growths, semi-ripe wood, hardwood, single leaves, buds and roots. Stem cuttings may be taken about 7-10cm (3-4in) in length of half-ripe shoots in July or August of such plants as cistus, hydrangeas, hebes and the like.
Some, such as those of camellias, may have a heel of the old wood attached Cheer cuttings), though most cuttings are prepared by trimming them just below a node or joint (`nodal’ cuttings) with a sharp knife or razor blade. The cuttings should be inserted to about a quarter of their depth in pots of moist sandy soil, or John Innes cutting compost, or a mixture of sand and peat, or in a sandy propagating bed in a cold frame. Such cuttings should be shaded from the direct sunlight and be lightly sprayed over with tepid water each morning until roots have formed. Any cuttings that show signs of damping off should be removed.
In the spring young shoots may be taken from the base of such plants as chrysanthemums and dahlias which have been brought into early growth in a warm greenhouse or frame. These are known as soft stem cuttings and after they have been prepared by trimming them cleanly below a node or joint and removing the lower leaves, they should be inserted to a quarter of their depth in moist, sandy soil in a propagating frame with a temperature of about 55°F (13°C).
Delphiniums, lupins, heleniums and many other plants, such as the somewhat tender lemon-scented verbena (Lippia citriodora), may be treated in this manner. Cuttings of the more tender plants such as dahlias may be rooted more quickly if the propagating frame is supplied with bottom heat and a very moist atmosphere is maintained, by inserting the cuttings in pots of moist sand or other rooting mixture, and plunging the pots in moist peat in the frame, and spraying them
overhead each day. However, as far as the hardier plants, such as lupins and delphiniums are concerned, too much heat and too moist an atmosphere may easily result in the loss of cuttings through damping-off disease or other fungus diseases. Once such soft stem cuttings have rooted they should be potted singly, or in some instances they may be planted out in the open, provided they are not neglected. They should be protected from direct sunlight and drying winds while they are becoming established.
Hard-wood cuttings sometimes referred to as naked cuttings, are taken in October or November, of pieces of trees, shrubs, gooseberries, currants, hedging plants, such as privet and lonicera, and various other plants. Climbing roses may also be increased in this manner, but the percentage of hybrid tea and floribunda roses that root is so poor that commercially it is not a practicable proposition.
The cuttings are made from pieces of the current year’s growth, about 25-30cm (9-12in) in length, pencil-thick, with a clean-cut made just below a bud eye. Remove all the leaves except a few at the top and insert the cuttings in sandy soil to a depth of about 10-15cm (4-5in), making the soil firm around the cuttings. Prepared cuttings of hedging plants, gooseberries, currants, and other really hardy plants, may be inserted in sandy soil in the open, choosing a reasonably sheltered place in partial shade—beside a hedge is often a suitable spot for a row of such cuttings. Cuttings of more choice shrubs should be placed in sandy soil in a cold frame, or have cloches placed over them. Most of these hard-wood cuttings will have made roots by the following spring, when they can be planted out or potted up and grown on for a while before they are planted out in their permanent positions.
Leaf cuttings
Healthy, well-developed leaves of numerous plants provide a useful means of propagation. Those that root particularly easily by this means include various begonias, such as Begonia rex, gloxinias, saintpaulias, streptocarpus, and some ferns, both tender and hardy. After removing a leaf from the parent plant make a few light incisions with .a sharp knife across the veins on the underside and then lay the leaf on the surface of moist compost, consisting of peat and sharp sand. Peg the leaf down gently; hairpins are useful for this purpose. Leaf cuttings should be shaded from direct sunlight and have a reasonably warm and moist atmosphere. Begonia leaves, among others, will produce roots quite quickly, even when just placed in a saucer of water, but the difficulty is that the roots are so tender that potting on the young plantlets is quite a problem.
Camellias are frequently increased by means of leaf-bud cuttings, which are similar, except that the leaf is taken from the current year’s growth, complete with a plump, dormant bud with a small
piece of stem wood attached. Such leaves are inserted in sharp, moist sand in pots or in a propagating frame in March in gentle heat. With the aid of mist propagation it is possible to deal with much larger numbers of cuttings over a longer period and the percentage that root is usually greater.
Rooting cuttings in polythene film
An interesting way of rooting hard-wood or semi-hard-wood cuttings without inserting them in the normal rooting compost is to use polythene film. The cuttings are prepared in the normal manner and a piece of film about 20— 25cm (8-9in) wide and, say 45cm (1ft) long, is placed on the propagating bench. On one half of this, along the length, is placed a layer of damp sphagnum moss. The cuttings are then placed on this (their bases may first be dipped in hormone rooting powder if desired) about 1-2cm (1/2 1in) apart, their tops projecting over the edge of the polythene strip. The lower half of the strip of film is then folded up over the moss and the cuttings. Then, starting at one end and working towards the other, the strip of film with the moss and cuttings is rolled up tightly and tied top and bottom with raffia or fillis. Roots should eventually form and these will be visible through the clear polythene. When all or most of the cuttings have rooted the roll can be untied and the cuttings potted up or planted out, taking care not to break the brittle young roots.
The advantages of this method are that once the roll has been tied up no further watering is needed as moisture will not evaporate through the film (the roll should, however, be kept out of direct sunshine, on the greenhouse shelf or bench, or even on a window-sill), and that a number of cuttings can be rooted in a quite small space.
Hygiene
When preparing cuttings, particularly soft stem cuttings which are liable to be attacked by soil-borne diseases or by virus diseases transmitted by insect vectors, it is advisable to take precautions against such attacks. Always use a clean razor blade or knife, if necessary sterilizing the blade in a sterilant or disinfectant such as a weak solution of Jeyes Fluid. When a batch of cuttings of, say, dahlias or chrysanthemums is being prepared for rooting it is essential to ensure that they do not flag while they are waiting to be inserted in the compost. As soon as each cutting has been taken from the chrysanthemum stool or dahlia tuber, drop it in a container of aired water to which a few drops of Jeyes Fluid has been added.
Virus diseases may be transmitted by sucking pests such as aphids. For this reason, when quantities of cuttings are to be rooted, it is advisable to fumigate the greenhouse beforehand and also to spray stools and tubers with a suitable insecticide and to dip cuttings in an insecticidal solution before they are rooted. Trouble with damping-off diseases can be prevented by watering John Innes cutting compost with Cheshunt Compound. This is less necessary with pure sand or sand/peat mixtures as both these should be reasonably sterile.
Root cuttings
These consist of pieces of root about 5cm (2in) in length taken from plants with fleshy roots, such as anchusas, oriental poppies, gypsophilas, verbascums, romneyas, seakale and horse-radish. This is an autumn or winter job, the roots being lifted and then cut into pieces of the required length. The cuttings are usually made from roots which are about the thickness of a pencil, though where seakale and horse-radish are concerned they are made from side-roots and may be thicker than this. When making the cuttings make a clean, flat cut across the top and make the base wedge-shaped, then there will be no problem as to which way up the cuttings are to be placed when they are rooted in deep boxes of sandy soil.
The top of the cuttings should only be just below the surface and the pieces of root can be placed side-by-side, horizontally or vertically (wedge-shaped end downwards), and made firm in the soil. The boxes should be stood in a cold frame or cold greenhouse for the winter months, and may be stood in the open in the spring. When top growth is evident, which is usually by the spring, the cuttings should be planted or potted up separately. With plants, such as herbaceous phlox, Primula denticulata, or the little alpine Morisia monantha, which have much thinner, thread-like roots, these may be treated in the same manner except they are merely placed lying on the soil in boxes, or pots, and then lightly covered with sandy soil. The greenhouse, evergreen, flowering bouvardias may also be increased in this manner, but with these it is best to take the cuttings in spring and bring them along in gentle warmth.
Pipings
The rooting of pipings is a method of propagation used primarily for members of the dianthus family, particularly carnations and pinks. Pipings are in effect a type of cutting, but instead of using a knife to make the cutting, the shoot is pulled out from the main stem. The tip of the leading shoot is held gently between the thumb and forefinger, just above the first node, and pulled until it slides out of the node where the first pair of leaves has formed. The main part of the stem should be held with the other hand. There is no need to prepare it in any further way, and the piping can be inserted in a sandy compost to root in the usual way. Pipings are usually taken in early summer from young non-flowering shoots.
Vine ‘eyes’ Pieces of dormant one-year vine rod, each with a plump bud, are cut into lengths of about 4cm (2in), which are virtually stem cuttings. With the aid of a sharp knife remove a strip of wood 3mm (1/4in) thick from the wood behind the bud to encourage root formation. The pieces of rod are then pegged down individually into pots containing sandy soil and placed in a propagating frame with a bottom heat of 75°F (24°C) and kept moist. When roots have formed and top growth is evident the pieces should be potted separately and grown on under glass in a temperature of about 60°F (16°C).
Layering
Numerous shrubs, such as rhododendrons, magnolias, syringas (lilacs), hardy heathers, as well as figs, loganberries and cultivated forms of blackberries, are readily increased by this means. With these plants the work is done in the autumn or during the dormant season, as with clematis, jasmine and honeysuckle. Border carnations and pinks, however, are layered in July, after they have flowered, and the layers will root in a matter of weeks in the warm soil. The more permanent shrubs may take six months or longer to develop sufficient roots for the layer to be severed from the parent plant.
A layer should consist of a long, healthy shoot that can be bent down to the ground where it is pegged down into moist soil to which peat and sharp sand have been added either in the open ground or into a pot filled with a similar compost. Before the layer is pegged down, or kept in place with a stone or brick, a cut should be made with a sharp knife on the underside of the stem, so that the stem is severed horizontally for about 3-5cm (1-2in), the cut being made so that it passes through a node or joint. This is the part which should be pegged into the soil. The object of making the cut is to check the flow of sap and the cut will then callus and roots develop at this point. The same object may be achieved with many shrubs by merely twisting the shoot, or bending it until it is partially broken, at the point where it is to be pegged into the soil. With such vigorous plants as the blackberry and loganberry all that is necessary is to peg down the tip of a stem and this will quickly make roots in moist soil. This is known as tip layering. With strawberries, the runners are pegged down in June and July. Roots are made quickly and the rooted layers can be severed from the parent plant in August and September and transplanted or potted.
Layers of clematis should not be made from the current year’s growth, but from parts of the stem that are 18 months old or more. This also is done in the dormant season and the same method applies to the climbing honeysuckles (loniceras).
Aerial layering or air layering
This method is useful with certain plants that cannot readily be layered in the soil because of their erect habit. It may be used with varying success with a wide range of plants, including camellias, prunus, liquidambars, tall rhododendrons which cannot be layered in the ordinary manner, conifers, and so on, as well as certain greenhouse plants, for example, Ficus elastica, the India-rubber plant, when it becomes leggy. The basic principles are the same as for ordinary layering, but as the branch cannot be bent to the ground, the ground must be taken to the branch. However, soil is not used, instead damp sphagnum moss is the rooting medium.
Another difference is that a complete ring is cut around the shoot with a sharp knife about 23cm (9in) from the apex and then a generous handful of damp sphagnum moss is placed all around the wound, after any leaves on this part of the stem have been removed, but not those at the tip. The moss is kept in place with a piece of polythene; black polythene used in a double layer is best for this purpose. This is then carefully tied top and bottom to form a neat little bundle. Healthy young pencil-thick shoots of ripe wood of the previous year’s growth should be chosen for air layering, not old, hard-wood. April is considered the best month to do this work, but in a late season May or early June may prove satisfactory. When roots are to be seen in the moss, the layer should be severed from the parent and the young plant very carefully potted in an appropriate soil compost. This is tricky, for at this stage the roots are tender and easily broken, also the period during which the plants are making further roots into the soil compost can be a difficult one, so that they will require careful attention and nursing until they have become adjusted to their new conditions. Careful shading from direct sun and daily spraying with tepid water will assist them at this period, either in a cold frame or cold greenhouse. Certain greenhouse plants may be propagated in this way and these will require much warmer conditions when they are being grown on. The time for an air layer to make roots varies considerably with the type of plant, in some instances it may be many months, though the time may often be reduced by the use of a hormone rooting powder sprinkled round the cut on the stem before damp
moss is placed round it.
Budding
This is a method widely used by commercial growers, in particular of roses and fruit trees. By selecting closely related root stocks on which selected buds are inserted vigorous plants are obtained more quickly than if they are propagated by other means. Budding is done from June to about mid-August and showery weather is the most favorable, hot dry weather being avoided whenever possible. A plump bud from the current year’s growth is selected and carefully cut out with the aid of a sharp budding knife. Start the cut about 2.5cm (1in) above the bud and end it about 2.5cm (1in) below. The bud, complete with a thin sliver of wood beneath it can then be removed, with a piece of leaf-stalk which is helpful when handling the bud. This should be trimmed back later. Next a neat, T-shaped incision is made into the bark of the stock plant and with the aid of the handle of the budding knife the layer of bark is opened so that the bud may be inserted in the T-cut, pushing the bud as far down the vertical cut as possible. It is most important that the bud is not allowed to become dry before it is put in position. Finally bind the bud in position with raffia or adhesive tape. Bush roses are budded as near as possible to ground level, but standard roses and weeping standard prunus, and the like, are budded on stocks 2-2.3m (6-7ft) in height (2.3-2.5m [4-4.5ift] for standard roses). If the bud turns brown and shrivels, this is evidence that the bud has not ‘taken’ ; this is usually apparent within three weeks. Where the rose bud has taken it will be necessary the following February to cut off the growing top of the rootstock, above the point at which the bud was inserted, leaving about 2.5cm (1 in) of the stem of the stock above the bud for protection.
Scales
Plump scales, mainly from lily bulbs, provide a useful means of increasing stock. These are best removed from the parent bulb soon after flowering, or in the autumn, and placed in boxes containing moist peat and sand. Small quantities can be put in polythene bags containing moist sphagnum moss where they will soon start to make roots. The bags should be hung in a cool, shady shed or garage. Careful potting will be necessary as the little roots are brittle and easily broken. Lilies increased in this manner will, of course, be true to color and will not vary as will plants raised from seed.
Gladiolus cormlets
At the base of gladiolus corms, when they are lifted in the autumn, will be found numerous corm-lets, known colloquially as ‘spawn’. Where good varieties are concerned it may be worthwhile removing and storing these cormlets, putting them in trays of dry peat and storing them in a frost-free place for the winter. In March or April, they should be planted out in well-drained beds to grow to a flowering size which is usually reached in three years.
Hyacinth bulb propagation
The two methods used by commercial growers to increase hyacinths are known as excavation and notching. Both give the same result, but the first method produces numerous small bulbs, while those on notched bulbs are larger in size but less numerous. With notched bulbs four or six cuts are made with a sharp knife across the base of the bulb, like the spokes of a wheel, to form a shallow V-shaped channel. The excavation method requires careful scooping out of the base of the bulb to leave a conical incision. In both instances, the base is then dusted with powdered chalk. The bulbs are then placed upside down in an airy room with a constant temperature of 68°F (20°C), and high humidity. This work is usually done in September and in about five weeks time bulbils will start to form on the base of the mother bulb. The temperature should then be raised to 75°F (24°C) and in November the bulbs, complete with bulbils, should be planted in shallow boxes of sharp sand and protected from frost for the winter. In the spring the bulbils are removed from the mother bulbs and stored in a dry condition until early autumn when they are planted up and grown on until they reach flowering size.
Mist
Modern electrically controlled mist propagation units are fitted with jets that emit a fine mist spray to envelop cuttings with moisture in order to raise the relative humidity. This used to be done with the aid of a hand syringe but it is much more accurately carried out by the ‘electronic leaf’ which is placed among the cuttings. As soon as the ‘leaf’ becomes dry the spray is turned on for a predetermined period. Cuttings inserted in a sandy propagating bed heated by electric soil-warming cables will root more quickly than in a cold frame, and with a mist unit installed it is not necessary to shade cuttings, except during very hot, sunny weather.
Soft stem cuttings rooted under mist must be potted at an early stage and grown on in a greenhouse before being hardened off. Semi-hard-wood cuttings can be left in the mist for a longer period as they do not usually make so much top growth, and hard-wood cuttings can remain in the cutting bed until the spring, if necessary. Mist propagation is not the answer to all the problems of rooting cuttings, but it is particularly useful with large-leaved evergreens, such as camellias, and it has also proved successful with acers (maples), large-flowered clematis hybrids, various conifers, dahlias, daphnes, hibiscus, ilex (holly), magnolias, mahonias, pittosporums, pyracanthas, rhododendrons and azaleas, syringas (lilacs) and viburnums.
Rooting compounds
Chemical substances, known as rooting hormones, are available both in liquid and powder form and are useful for accelerating the rooting of cuttings that may otherwise prove difficult. They are not the answer to the rooting of all types of cuttings but when used according to the maker’s instructions can prove to be a valuable aid. With the powder, the cutting is prepared and then the base is dipped into the powder before being inserted in the rooting compost. When using the liquid formulations the prepared cuttings are stood in a container with 2-5cm (1-2in) of the liquid in the bottom for some hours before being inserted in the rooting compost.
The actual substances are used in minute quantities. For instance, one of them, naphthoxyacetic acid is used at the rates of between 2 parts and 25 parts per million. Three other substances, alpha-naphthalene-acetic acid, indolylbutric acid and beta-indolyl-acetic acid, are used at rates ranging from 10-200 parts per million, depending on the type of cutting which is being rooted.
