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7. Propagation of Hibiscus

Although there are four ways of reproducing hibiscus plants of a particular variety, only two are commonly used: cuttings and grafting. The other two, tissue culture and air layering, are not used by the average gardener. Hibiscus grown from seed always have seed variation, particularly the later hybrids which may revert to the types used in their formation. A plant grown from cuttings or grafts will be identical to the parent plant in leaf, flower, growth etc.

Cuttings

Parts of a plant that are taken from it to be used for vegetative propagation are called cuttings. With hibiscus, parts of the stem are taken, and classified according to the type of wood as tip cuttings, medium wood cuttings and hardwood cuttings.

Tip Cuttings

These are usually taken in summer, when the new growth is most vigorous. Proper handling of these cuttings is of prime importance in successfully developing new plants. Do not take a quantity of tip cuttings and submerge them in a bucket of water for long periods. Simply submerge them in a solution of water and Formula 20 for a minute or so, then place them under a moist cloth or in a plastic bag with some water sprinkled inside the bag. Keep them out of the sun to prevent wilting. Take tip cuttings 10 15 cm (4 6 in) long. Make a clean cut roughly at a 45 degree angle through an eye. (There is an eye at the base of each leaf.) Dip them in a hormonal rooting powder suitable for softwood cuttings, and place them in the rooting medium. This can be coarse river sand, perlite and peat, vermiculite and peat, or a mixture of perlite, sand and peat. If the leaves are large they should have the leaf area reduced by half. The cuttings do better if placed in single propagating tubes, however they may be placed in one community pot. Glasshouses with misting devices are preferred for tip cuttings. For the home gardener a small frame covered with clear plastic will do provided the plants are sprinkled several times throughout the day to prevent excessive transpiration.

Medium Wood Cuttings

These are taken in autumn as the soft wood begins to mature, and are mainly taken by nurserymen wishing to build up a stock of the particular variety. These cuttings are not popular with home gardeners because taking them removes flowering wood; also they do not have time to establish themselves fully before the cooler weather arrives. Firm wood slightly smaller than pencil thickness is selected and all but the three top leaves removed. These are then reduced by half, and a diagonal cut through an eye about 7.5 cm (3 in) below the bottom leaf is made on the stem. The cutting is now ready for planting. Dip it into a medium wood hormone powder (Seradix No 2) and plant in individual propagating tubes in the same rooting medium as for tip cuttings. Place under glass or cover. Do not repot until spring.

Hardwood Cuttings

The easiest way of propagating hibiscus is by hardwood cuttings taken the last month of winter or in early spring. This is the normal pruning time anyway, so avail yourself of the ample supply of wood. Make sure that you have a small makeshift glasshouse or coldframe ready to protect the cuttings from wind, prevent them from drying out, and provide the necessary extra warmth required to encourage root growth.

Select strong, straight wood, pencil thickness or a little larger. Weak twisted stems produce equivalent plants; the better the wood the better the plants. Remove all the leaves, by bending them backward against the stem or by cutting off with secateurs. Do not pull or tug them particularly if they are a little dry, for they will strip, pulling out the eyes and tearing the bark. Using a sharp knife make a cut at about 45 degrees through an eye at the base of the cutting, slicing right through in one even stroke. The cutting is then trimmed to a length of 12.5 - 15 cm (5 - 6 in). These cuttings may be placed either in individual propagating tubes or in 15 cm (6 in) community pots, which will hold about thirty cuttings. Hardwood cuttings seem to prefer coarse river sand with a little peat mixed through it as a rooting medium, however various mixtures of perlite and peat, or perlite, sand and peat have all been successful.

Once the cuttings are struck they may be potted on into larger pots using a mixture of two parts sandy loam, one part coarse sand, one part peat, one part old cow manure (fine), and one part leaf mould. To remove the rooted cutings from the community pots without damaging their roots, separate them in a bucket of clear water before potting. Always water them with a solution of water and Formula 20 after potting. The cuttings should be dipped in a hormone powder before planting, preferably a medium or hard wood type (Seradix No 2 or 3). Most people plant their cuttings too deep. Insert them into the rooting medium to a depth of 2.5 to 3.7 cm (1 - 1  in).
There are numerous types of propagating units available which will aid the home gardener in the striking of cuttings and raising of seed. Investment in one of these units will ensure more success with propagation and increase the pleasure of watching plants created by you growing and maturing.

Grafting

Grafting is used to increase the number of plants from an existing variety or to establish a weakgrowing variety on more vigorous roots. Cuttings of a strong rootstock such as H. arnottianus (Wilder's White) or `Albo Lacinatus' (`Ruth Wilcox') are grown in pots to strong, sturdy plants with wood about the diameter of a pencil. If this understock plant is fed with a soluble fertiliser a week before grafting, growth of the scion will be accelerated.

When choosing rootstock for grafting, species like H. schizopetalus that grow tall and whip like are not recommended. They are small in girth, and scions grafted on them will grow larger in diameter than the stock, resulting in weak grafts. We find that there are different understocks that are more suitable in different climates. For instance some growers use `The President' or `Pride of Hankins' (`Landersii') in their area in preference to `Albo-Lacinatus' and vice versa. A good guide is to study the older types of hibiscus in your area and select the strongest, hardiest, most vigorous and most disease resistant, particularly to root rots. You will find that there will be a number of varieties that you will be able to use as understock.

The most commonly used methods are the side graft, tip graft and veneer graft (see drawings). The variety to be grafted to the root or understock is called a scion. This wood is cut into lengths containing two or three eyes, showing green buds.

If the buds are brown and dormant the scion will grow but it will take longer. Remember that the lowest bud of the scion should fit close to the rootstock to produce a straight and well shaped plant. Protect the plant from wind and drying out until the buds emerge as leaves. This can be achieved by placing a plastic bag over it until the graft is established and keeping in the shade. If the rootstock is a vigorous grower, within two or four weeks a tissue, comparable to scar tissue in animals, will have formed over the cut surfaces of the graft. Grafting tape is best left on for six to eight weeks, however any stronger binding should now be loosened to prevent strangulation. Once the new buds have several leaves, the leaves and eyes of the rootstock may be cut out. The plant should carry a tag with the name of scion and date grafted.

Many growers wax the grafts to prevent drying out and to exclude moisture and disease organisms. Use grafting wax or grafting tar (Colgraft or Emastak). Using a small paint brush, paint the grafting wax over the entire graft, sealing it completely. You need not remove the wax, for it will break off as you remove the grafting tape. When using the grafting tar, completely seal the union of the scion and rootstock and the cut on the scion. Do not cover the buds or eyes!

The success of the grafting operation is dependent upon acquiring a skill or `feel' in the procedure. It takes a certain amount of practice to get this feel and the more grafting you do the more proficient you become. You won't do it perfectly the first time, but each one you do after will get better. When pruning a bush save a long branch to practice on, making one slanting cut after another until you can make even, regular cuts that will match perfectly on the sides (without cutting your fingers).

Get the best knife you can find made of good quality steel which will hold an edge; there are special grafting knives by various manufacturers including. Kunde which are designed for the job. Keep it clean and sharp and protect its edge from contact with other tools. Do not use it for any other purpose except cutting plant material, and apply a thin coat of oil or vaseline to the blade when not in use for any length of time. Learn how to hone a fine edge with a good fine grain carborundum stone and how to whet a razor edge. Grafting knives are sharpened on one side only, either for left or right-handed people. Lay the blade almost flat on the stone and sharpen against the edge as though you were cutting the stone, moving the blade toward you at an angle of about 30. Some people prefer to move the blade in a circular motion on the stone. Be careful to keep the surface of the stone perfectly smooth and even. Remove any burs by stropping on leather or very fine emery paper. Plant fibres and acids in the tissues slowly erode and corrode the fine knife edge, so it should be stropped now and again. If you keep a raw potato handy and run the knife edge through it occasionally the potato will clean the knife and help it stay sharp longer. The knife should be able to slice through the stringy fibres of the wood at a small angle without bruising or tearing. It is important that the knife edge is keen enough to make smooth cuts that match perfectly with an even contact between surfaces. The popular utility knives with interchangeable blades may be used as long as the user takes care, for they are very sharp. They are also cumbersome, but with practice one becomes just as proficient with them as with the normal knives. The changing of blades takes but a second and one is always assured of a very sharp edge. Stick to a well known brand such as Stanley, for the blades of some brands are of inferior steel with poor cutting edges.

Always try to match the thickness of the scion with an understock of the same thickness. This is not always possible and it is not necessary to match both sides of the cambium layers, one matching cambium layer sufficing, but a better union will result if both sides are matched. The cambium is the soft green layer of tissue between the white wood and the bark. Without touching the cut surfaces with the fingers, match them and bind tightly together with plastic grafting tape. Sometimes Twistems can be used. Rapid healing of the graft union is necessary so that the buds of the scion may obtain water and nutrients from the rootstock by the time they begin to sprout.

Side Graft
This graft is also known as the side wedge graft and is probably the graft most commonly used for hibiscus. A piece of scion wood, preferably not longer than 7 cm (3 in) with two or more eyes, is cut and sharpened to a pointed wedge. This wedge must be cut with one even stroke on each side. A slanting downward cut equal in length to the scion cut is made into the rootstock at an angle of about 60. The wedge is inserted with the buds pointing up. After matching the cambium layer on at least one side, the graft is then tightly bound with grafting tape and the union sealed with grafting tar or mastic. Trim off any eyes on the understock below the graft to prevent these from shooting, and also trim a few centimetres from the top of the plant, leaving enough leaves to enable the plant to recover rapidly. Once the scion has begun to grow and the first leaves are beginning to mature, then the top section of the rootstock is cut off as close to the graft as possible. Plants that have been grafted come away a lot faster if placed under glass or otherwise under optimum conditions. Side grafts `take' much better when the plants are growing vigorously, usually in summer and autumn, although they can be done at other times of the year except winter, unless under glass.

The Wedge or Cleft Graft
This method is used by most commercial growers as it provides a better union between the scion and the rootstock. It is mainly done in spring when ample grafting material is available from prunings. The rootstocks are grown in small, easy to handle pots, 7.5 - 10 cm (3 - 4 in), until about pencil thickness in diameter. The scions are cut from wood the same diameter, or as close as possible, and are made no longer than 7 cm (3 in) with at least two eyes. The rootstock is cut off about 10 cm (4 in) above the pot and all the eyes removed. A cut is then made right in the centre of the rootstock about 2.5 cm (1 in) deep, and the scion cut to make a matching wedge shape. The wedge is placed in the cut in the rootstock, tied with grafting tape and sealed with grafting mastic. If placed in a glasshouse these grafts begin to shoot out within a few weeks.

There is a variation to this which gives the grafter an even better union. After the top of the rootstock has been removed and the cut made down the middle, the bark is peeled back on one side. The section of white wood now visible is cut out for a length of about 2.5 cm (1 in), and the scion wedge, cut less acute than before, is placed against the remaining white wood with the cambiums matching. The bark is placed against the other side of the scion. This union is more uniform and is advised when grafting wood over 13 mm ( in) thick.

Tip Graft
This is almost the same as the wedge graft except that it is done on green tip wood. Cut a scion with several eyes below the growing tip, which is removed to prevent wilting, and sharpen the bottom of it to a wedge. Cut the top of the rootstock and splice it down the centre as for the wedge graft. Insert the wedge into the rootstock matching the cambium and bind tightly. Covering with a plastic bag will keep the green wood from drying out. Use a stick or stake in the pot to hold the plastic away from the scion, and a rubber band around pot and bag to keep the moisture in. Place the plant in the shade for about a week and gradually harden off, removing the bag before the plant is placed in the sun. This method of grafting is mainly done during late summer or early autumn just as the green wood begins to firm. This graft can also be reversed, the rootstock being sharpened to a wedge and inserted into a corresponding notch cut in the scion. The advantage of this method is that moisture is kept out better and the downward flowing sap in the cambium helps the scion to callus faster. This method is called saddle grafting.

Veneer Graft
A smooth, shallow cut about 25 mm (1 in) long is made diagonally into the rootstock. At the base of this cut, a second short inward and downward cut is made, intersecting the first cut, so as to remove the piece of wood and bark and leave a small notch in the rootstock. On the scion wood, make a long matching cut on one side and a very short one at the base on the opposite side. Fit the scion into the notch on the rootstock matching the cambium layers at least on one side, with the notch at the bottom of the rootstock forming a cap to cover the end of the scion wood. Bind tightly with grafting tape and apply grafting tar. This is also known as a chip graft and seems to provide a good percentage of `takes'. Cut off the remainder of the rootstock once the scion has produced mature leaves.

While it is possible to place many grafts of different varieties on a single large bush, this is not advised unless the growth patterns of the varieties grafted are identical; if there are various growth habits in the scions, the stronger main plant will prevail. However it is possible to place many grafts on the one bush and remove them once they have taken either by air layering or by cutting them off and treating them as cuttings.

Cutting Grafts
A new method of grafting has been developed by commercial nurseries to provide good, well-established grafted plants to the public at reasonable prices. This method is called cutting grafts and it involves the taking of cuttings for understocks and then grafting, usually by wedge or cleft grafts, the scions of the required variety onto them. The cutting grafts are then treated like normal cuttings and placed in a propagating medium until struck and ready for potting. This way of producing plants is much faster for nurserymen, however it is not practical for the home gardener as he does not usually have the ideal conditions available. Cutting grafts should be taken in spring.

A grafted plant must be examined from time to time to detect shoots from the rootstock emerging below the graft. These must be removed as they may dominate or take over the entire plant, choking out the desired growth of the scion. These are easy to detect as they usually appear as strong `water shoots', and of course there will be a marked foliage variation between the rootstock and scion.

Many hard to propagate and slow growing varieties have been successfully grafted, and when these varieties are placed onto a strong, hardy, disease resistant root system the results are amazing. They perform so much better than most and more hybrid hibiscus are now being grafted. Always look for grafted plants of later varieties particularly if you live in a cooler area. Most nurserymen now graft the varieties which in their opinion warrant grafting.

Air layering (marcottage, or mossing off)
This method of propagation will provide a larger plant in a shorter time. The best time for air-layering is in the warm weather. A healthy, upright growing branch is girdled completely with two cuts about 2.5 cm (1 in) apart and the bark and green cambium are removed completely down to the white wood. A hormone rooting powder maybe applied to the upper side of the cut. (Steps 1 and 2 in diagram.)

Use plain water and place sphagnum moss in it to soak. Next, squeeze a double handful of the well-soaked moss relatively dry and wrap it around the cut area, covered by apiece of plastic, then a 15 x 15 cm (6 x 6 in) sheet of aluminium foil. A layer of brown paper may be placed over the foil and tied securely. The plastic and foil will retain the moisture, and the brown paper will exclude light and deter birds that may peck holes and let the moss get dry. (Steps 3 and 4 in diagram.)

When examination shows that a good ball of roots has developed, the branch is cut off below the ball, and plastic and foil carefully removed without disturbing the roots and moss. Do not remove the moss! The end of the branch is then trimmed as close to the ball as possible before being placed in a bucket of water containing Formula 20. Allow the plant to become saturated then pot and water thoroughly. It is advisable to cut back some of the leaves and to protect from wind and sun until the new plant is well established. Place the potted air-layer in light shade for two or three weeks for best results. Fertilise lightly in thirty days.

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