Methods of Propagation
Let us turn our attention for a few minutes to the structure of plants.
In every form of life, Nature appears to have a double object. In the first place, there is the development of the individual life in flowering plants—this is seen in the growth of the stems, branches, leaves, and in the second place the passing on of that life to a new life seen in the production of seeds. In the case of the original plant—animal cells which are believed to have been the origin of all the life on this planet, the difference is quite apparent. A single cell can increase itself by the simple method of splitting up into two parts. This is, in fact, merely a multiplication of the same cell life. It can also unite with another cell and then redivide. The result of this is that new lives are formed which partake of the characteristics of both parent cells.
Gardeners often take advantage of the non-sexual methods of repro-duction when they have plants of a especially good type that they wish to increase. They have studied Nature’s ways of multiplying special plants and they have adapted, and perhaps improved, on her methods. Apart from seed raising, every method of propagating plants practised in the garden results in the production of new plants which are identical with the parent. Some of the most common of these methods will be described.
The simplest of all methods of increasing the stock of plants is by root division. The greater number of the common garden perennial flowers, and a good many inhabitants of the kitchen garden, have roots which can easily be broken into pieces. Any plant which produces a root of this kind can be increased by simple division.
In the case of border plants that make a crowded mass of roots, such as Michaelmas Daisies and Heleniums, regular division is advisable even if an increase in stock is not wanted, to avoid overcrowding. If roots are left unchecked, they send up more stems than can comfortably be accommodated in the limited space they occupy and the resulting flowers and foliage are poor.
The easiest way to divide large clumps is to lift them bodily with a deep digging fork, and break off, either with a small handfork or trowel, the outer pieces of the clumps. This is where the newest roots are, and these new roots make the finest plants, and produce the best flowers. Very large overgrown clumps should never be replanted in the mixed border.
Should there be any difficulty in breaking a large clump into pieces, the best way is to drive in two handforks, back to back, into the centre of the plant, and then lever two pieces apart. This is often necessary in the case of plants where the root-stock is of a hard, stubborn nature.
Bulbous plants are frequently found, on lifting, to have a number of smaller bulbs attached to the old bulb. This again is a natural way of producing new plants which will be identical with the parent plant. These small bulbs or offsets can be taken off, and replanted just as if they were older plants. They will gradually increase in size until they are normal flowering plants. The formation of small bulbs is encouraged by damage to the base of a large bulb. This fact is taken advantage of where bulb growers wish to increase rapidly a stock of any particular bulb. They score across the base, and this results in the formation of numerous new small bulbs. Similar small bulbs or bulbils are often found in the axils of the leaves, especially on. These bulbils, removed and replanted, will also form new plants.
The amateur gardener who replants offsets or bulbils of any kind should always make a note of the variety of plant so that he can use them effectively when they reach flowering size.
which have a tuberous root-stock, such as the , are often increased by cutting the tuber into pieces. Each piece cut should have an eye to it. Potatoes are frequently cut in this way when the seed bought is on the large side. It is generally recommended that any cut tubers should be allowed to remain in the air for a few hours, or days, before replanting. A skin or callous then forms over the cut, and disease spores from the are less likely to enter.
Just as tuberous plants are increased by cutting the roots into portions, so can the fleshy roots of plants such as the Oriental Poppy be formed into, to increase the stock. In the case of the Oriental Poppy, pieces of the root about the length of a finger are cut cleanly across, above and below, and planted vertically in the soil, with about two or three inches of soil above the top. Seakale is another plant which is increased in this way. This method of making root is even more certain to succeed than the method of from the leaf stems, and it is certainly a useful way of increasing rapidly many of the common .
Plants have the power of developing roots from almost any portion of the plant. That is why it is comparatively simple to raise fresh plants from cuttings. The only difficulty is that, as the new pieces inserted have no root, they are not able to take up moisture at the normal rate. If the atmosphere is dry, and the cutting inserted has a large leaf surface, from which moisture is being constantly given off the cutting dries and dies. By maintaining a moist atmosphere all round the cutting, the gardener makes it possible for the plant to keep moist while the roots are forming. Bell glasses (or jam jars) inverted over the plants, or the use of a propagating frame which is kept close shut, or the use of a closed cold frame, all serve the same purpose—that of keeping a stationary moist atmosphere round the cutting, until the roots have formed.
Cuttings of deciduous trees and shrubs are far best made at the end of summer, the reason being that there is no leaf surface in winter, and consequently little loss by evaporation. Plant roots form before the new leaves of spring call for more soil moisture. The difficulty that arises with cuttings under glass is that the stationary moist atmosphere may easily set up the disease known as “damping off.” In which case the plant dies as surely as if it were left to shrivel through dryness. To avoid trouble of this kind, cuttings are rooted either in pure sand, or very sandy. Actually cuttings root best in pure moist sand, but as soon as the roots begin to grow the plants demand a certain amount of food, which the sand does not contain. So that if a cutting can be rooted in a sandy compost, instead of pure sand, it is an advantage, as the new plant can be left without disturbance for a longer period.
A useful way to prevent damping-off amongst cuttings, is to sterilize both the cutting and the soil of the propagating frame before the cutting is inserted. Cuttings can be put into a weak, pale, rose-coloured solution of permanganate of potash crystals in water, for a few hours before they are to be inserted in the propagator. The sand or soil used for the propagating frame can be sterilized by watering well with the same solution.
Cuttings in the Open
When it is intended to root cuttings in the open, there is always a certain amount of risk, and occasional losses will occur due to long periods of drought, etc. However, cuttings of many garden plants may be rooted comparatively easily. The secret is to choose pieces in just the right condition. Very hard wood does not send out roots so readily as does newer growth, but very new, tender, sappy growth is much more likely to suffer in dry or cold weather than are older leaves and stems. The best thing therefore is to choose half-ripened stems. (I find it best to cut off the rather tender tops of Rose cuttings, for instance, when inserting pieces of ramblers, etc., in the open garden, as I always do at pruning time.)
Another point is to insert the cuttings at a time of the year when showers are likely to be frequent, and drying winds few, and also when the soil and atmosphere are warm, warmth being essential for production of new growth.
It is for these various reasons that cuttings of Roses and shrubs and of bedding plants such as Geraniums, Violas, etc., to be rooted outdoors, are usually taken towards the end of summer, that is in August and September. The cuttings are inserted in any shaded part of the garden, where bright sunshine will not dry them too rapidly, and as autumn showers can reasonably be expected, cuttings inserted at this time have the best possible chance of success.
Where to Cut
In most plants it is found that roots form readily at the joints. The common practice is, therefore, to “make” a cutting by cutting immediately below the leaf joint. Some plants are best just pulled out at the joint. Pink “pipings,” for instance, can be pulled off in this way. The only other thing to do in “making” a cutting is to take off a few of the lower leaves from the stem before inserting it in the sand. The reason for this is that the leaf, being rather more succulent than the stem, is more liable to damp off, and it is inadvisable for leaves to be below the soil level.
In a few cases, such as, for instance, in the case of Willows and Clematis, roots appear to form more readily from the parts of the stem between joints, and cuts are usually made there in preference to just below the joints. These are called internodal cuttings.
In some plants it is more convenient to make cuttings from leaves.Rex is one of the best-known examples of this. This is the Begonia which has the large ornamental leaves of variegated colouring. If a leaf is taken and notched on the underneath side in several places, and then laid over moist sand in pans, and pegged down where the notches are, so that it comes in actual contact with the sand, roots will quickly form. Each piece of leaf with the roots so formed can then be separated, and potted up as a new plant. Some leaves will form new plants at the edge. For instance, a large leaf of Bryophyllum laid on damp sandy soil, as in the case of the Begonia, and kept moist, will produce new plants all round the outer edge.
A common trouble with someone who grows indoor, is that some of them tend to become tall and “leggy” and unsuitable for table decorations. The Aralia is a common example of this. After a number of years it usually presents a long-legged appearance, which is anything but beautiful. Cutting the plant down to near the soil-level would spoil its appearance, and it is better to induce the plant to make roots, higher on the stem and to repot the top with the new roots.
To do this, the operation of ringing is practised. With a sharp knife a ring of the outer bark is removed from the main stem, at the part where the new roots are wanted, that is, fairly near the green top. After this, moist soil must be packed and held round this ringed part until the roots have formed. The easiest way to do this is to split a flower pot in two halves vertically, and replace the halves round the stem of the plant, filling the pot with soil and binding it into position on the stem. A few canes pushed into the soil of the old pot will hold the split pot more securely. After the roots have formed, the lower portion below the new roots is cut away, and the top re-potted. If a split flower pot is not used, moss can be bound round the ring and kept moist until the roots form. Ringing is often adopted with other plants, such as Tree Carnations, Dracaena, etc.
Layering is a form of plant increase which Nature frequently practises. The Bramble, for instance, sends out long canes, which gradually bend their tips down towards the soil; as the tips touch moist soil they send out roots, and a fresh plant is formed. The gardener practises the same operation in order to increase such plants as Loganberries, and a good many of the ornamental shrubs. He also practises it with some of the border plants as, for instance, Carnations. Strawberries are increased in the same way.
The operation ofis most commonly practised with Carnations in the amateur’s garden and will be described in detail. Other forms of layering are done on exactly the same principle. The first essential for layering Carnations is that the soil round the plant should be vacant for a space of, say, 6-12 in. all round, and it should be of light open texture. The best thing to do is to surround the plant with a 2 or 3 in. layer of fresh soil (which should include wood ashes and mortar rubble) before the layering is begun.
The next essential is that the plants shall be well provided with side growths fit for layering, that is, side growths that are not carrying flowers.
The actual operation of layering is rather similar to taking cuttings, except that each cutting is left partly attached to a parent plant until the roots have formed. It is therefore not so likely to succumb to drought, or other troubles, since it has the sustenance of the parent plant on which to fall back.
Each of the side growths to be layered is stripped of two or three pairs of leaves from a part of the stem, say, about 3 or 4 in. from the top. After this, a slanting cut is made about two-thirds of the way through the stem, the cut being made upwards. This part of the stem is then bent down into the prepared soil, so that the cut is open, and a peg of some sort is pushed in to hold the plant firmly in position. The soil is then pressed well round it, and the operation is complete.
At the end of about three weeks roots should have formed at the place where the stem was cut. It is not, however, advisable to move the layer for another few weeks, though it can be severed from the parent plant. It is best to leave it where it is until about eight weeks after layering and then to move the new plant to permanent quarters.
Layering of Carnations is usually done about July and the plants are then ready for autumn planting in fresh borders.
In the case of hard-wooded shrubs, layering is more satisfactory than taking cuttings, but it frequently takes some considerable time for roots to form. In the case ofit may not be possible to move the root layer for about twelve months.
Budding is a form of plant propagation practised in order to save time. If a single bud of a new variety of rose is grafted, for instance, on to a strong healthy brier long strong shoots of the new variety will soon develop. Budding is also practised because some of the best varieties of roses or fruits will not grow strongly on their own roots. For whatever reason budding is done the operation is the same.
The tool needed is a budding knife with a very sharp cutting blade and blunt pointed handle. Budding can only be practised at a time of year when the sap is active, so that the bark of the stem will separate easily from the wood. For budding, a healthy bud on wood of the current year’s growth must also be used. The operation is quite simple.
A T-shaped cut is made in the bark of the stock (that is the brier or tree on which a new variety is to be grafted). The cut is opened with the blunt handle of the budding knife, the bark being eased away from the wood and turned back to allow for the insertion of the bud. For this the blunt-pointed handle of the knife is used.
The bud to be inserted must be prepared only immediately beforehand, otherwise the bud begins to dry, and will not unite with the stock. Preparation of the bud consists in making a semi-circular cut in the stem behind the bud so that the bud is cut out with a portion of bark and wood attached. (The bud is a dormant leaf bud, not a flower bud.) From the back of this the piece of wood is removed, leaving the bud only with the bark. This must be done rather carefully otherwise the bud comes out with the wood.
Before it becomes dry, the piece of bark with the bud is slipped into the T-shaped opening, and the cut edges pressed back in position so that the bud and bark attached are held closely against the inner wood of the stock. Raffia is then bound round to keep them firmly in position. The raffia should pass over all the broken edges of the bark, but should leave the bud exposed.
In a very short time, say about three or four weeks, it will be possible to tell whether the budding is successful. Either the bud will shrivel and die, or it will plump up, and it will be quite evident that it has united with the stock. When this happens the raffia is cut, so that sap is not impeded in reaching the bud.
Should a shapely standard be desired, it is usual to bud the stock in two or three places, as less training is subsequently necessary to produce a good bud.
Grafting is an operation similar to budding, with the exception of the fact that instead of a single dormant bud, a whole shoot of one plant is grafted on to the stock. Several forms ofare practised. All, however, are on the same principle. The scion must be joined with the stock in such a way that the cambium layers of each meet together. The cambium layer is the layer between the bark and the pith of a tree.
If the stock and scion are of the same size a simple slanting cut can be made and the two put together and held in position with grafting wax and raffia. If there is considerable difference in size, the smaller scion is inserted at the side of the stock so that the cambium layers meet. Cuts in all cases must be freshly made immediately before the union, otherwise the grafting will be unsuccessful.
The different names given to the kinds of grafting, merely refer to the shape of cut which is made in the scion.
CLEFT GRAFTING is when a cleft or V-shaped cut is made in the stock and the scion is cut to a wedge shape, so that it fits in the cleft.
SADDLE GRAFTING is when the shape of the cut in the scion is like an inverted W so that the scion sits over the stock.
RIND GRAFTING is when two or three cuttings are inserted on the outer edge or rind of the tree.
Inarching is a somewhat similar practice to grafting, sometimes done in the case of vines. The stems from two vines are brought close together and a piece cut from the bark of each. The two surfaces are pressed together and the join is sealed over as in grafting. When the union is complete the top of the unwanted vine is cut off, and the other vine separated below the join so that the top of the wanted vine is left on the inferior stock.
Special grafting wax is sold in small quantities for use by amateur gardeners. It is better to buy this than to mix a homemade supply. It is a soft putty-like substance which, when pressed round the graft, holds it firmly and prevents the access of rain, or keen-drying winds, to the cut-portions of the tree or shrub.
AFTER BUDDING OR GRAFTING only the newly grafted buds are allowed to grow on the plant in subsequent seasons. The tops of budded plants are cut back in early spring to just beyond the new bud, and any growths developing on the old wood below the bud or graft are rubbed off at once.