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8. Hybridisation

The best time to hybridise hibiscus is from autumn to early winter. The cooler weather is ideal, as high temperatures dry out or inhibit the pollen so that it is not as viable. Pollen may be stored in vials in the refrigerator until a wanted female parent blooms.


The parts of a hibiscus flower

When the bloom first opens, the anthers bear light coloured kidney shaped sacs. As the morning progresses these open or dehisce, and bright yellow pollen is exposed. This pollen is now ready to apply to the stigma pads of the selected pod parent or female. These pads are receptive even before the bloom opens. The pollen may be applied with a soft brush, or the bloom of the pollen parent may be picked and the pollen applied directly to the stigma pads, taking care to cover each pad thoroughly. Day old pollen may be used if it has been kept in isolation, but the pod parent must be fresh, so that the stigma pads are sticky and the pollen will adhere to them. Each grain of pollen then grows a tube down through the style and hopefully fertilises an ovule in the ovary (see line drawing).

At this point the cross should be entered in a stud book, giving the cross number, date, name of pod parent (female) and name of pollen parent (male), leaving space to enter the date of harvest and number of seeds. This will all go on one line in the book. A light tag should be attached to the stem of the pollinated flower, giving the cross number, the date, and the names of both parents, mother first and father second. When crossing two singles there is a much better chance of getting singles than doubles, although doubles will occasionally result. When crossing a single and a double the chances of getting singles and doubles are roughly equal. Most double hibiscus, but not all, are useless as female parents because of the arrangement of their floral parts. They can however be used as pollen parents.

After the petals fall the fertilised ovary enlarges. In a few days the calyx tips should be trimmed away carefully to prevent them harbouring insects. It is important to keep insects off the pod in the early stages, for sometimes they will sting a seed capsule and cause one of the sections to die. More seeds are lost to insects than any other cause. It is a good idea to carry with you in the garden an aerosol can of insecticide to spray the pods or a puffer pack of insecticide dust. The pod will ripen in forty to ninety days, turning from apple green to light brown. At the earliest sign of cracking open, a square of nylon net may be tied around the pod to prevent loss of seed. When the pod cracks open it should be picked, the seeds counted, placed in a shallow container to dry, then transferred to an envelope or box marked with the cross number, date, and other information. In general the larger the seed, the larger the flowers will be.

Some hybridisers plant the seed immediately, others let is dry for several days or even several months. Sometimes it is a good idea to wait until spring before sowing the seeds, so the seedlings have a full growing season before them before the winter comes, unless of course you have glasshouse conditions available. A suitable medium must be mixed in which to sow the seed. Vermiculite and peat, perlite and peat, sand and peat or compressed peat blocks are ideal. A depression 6 mm ( in) deep should be made in the medium to receive the seed. It is important that the planting medium be sterile to avoid diseases. In profile, the seed appears much like a human head. Hold the seed by the face to protect the embryo and then with a single edged razor blade (Gem type) or sharp utility knife, nick or scalp the rounded top of the head until a whitetop appears. This hastens germination. If you have difficulty finding the top of the head, take the seed between your thumb and finger and roll it a couple of times and it will stop in the right position. Because it is tapered on the bottom it will stop with the narrowest part down and you can nick the top of the head. Drop the seed in the depression you have made, cover it with sterile sand, and moisten thoroughly. When properly nicked and planted seeds will germinate in six to thirty days.

After the first four leaves appear, the seedlings should be potted, and if peat pots were used they must be covered with potting soil. Use a sterile sandy soil. Be sure to keep baby seedlings on the dry side if they are in a heavy soil medium. Pots for young seedlings should be sterile. Once established, seedlings may be planted directly into garden beds.
Hibiscus seedlings in full sun tend toward development of stocky, branched plants, with the possibility of earlier bloom. Dense shade will definitely retard the first bloom. Tip cuttings from young seedlings will outgrow the seedlings and bloom earlier. Take tips about 10 cm (4 in) long when the seedlings are about 30 cm (1 ft) high and propagate under mist or graft onto suitable understock.

Most seedlings will bloom in ten to fourteen months, some may take longer. Do not cut back as this will delay the flowering. Retain only the best seedlings, those with promise. Discard those which are undesirable, to help minimise the proliferation of undesirable seedlings. It is worthwhile to observe the plants for a year or two after they have begun to bloom before releasing them or registering them with the Hibiscus Society. In your breeding program, use only prolific bloomers with fully overlapped petals, and a heavy to medium textured flower. This should ensure that at least you will have quality. To be a really worthwhile seedling it must have acceptable qualities that are better than any other variety in its colour range. Out of twenty seeds from the same pod each will differ in colour or colour tones, colour of eye zone and petal formation. Don't be seduced by the loveliness of a new seedling which is not up to standard; discard it! Space in a garden is valuable and a bad plant takes up as much room as a good one.

If you are sincerely interested in raising new varieties of hibiscus from seed, then why not join a hibiscus society. The American and Australian Hibiscus Societies have what is known as a `seed bank' and members of these societies who are hybridising and have more seeds than they care to plant, send them to the seed bank officer of each society with the following information: parent identity mother first then father then date of cross. These seeds are then available to members of the societies. This of course is only one of the benefits one gains from a society. The latest up-to-date cultural hints and happenings in the world of hibiscus are available to members through periodic journals.

Mutations or Sports

These sometimes occur on a plant for no apparent reason, it just appears to be a freak of nature. One or more branches on a bush produces a completely different coloured flower, but usually has the same foliage. In some cases however the foliage may differ (e.g. turn yellow or variegated, purplish or deeper green). If the sport is good enough it can be reproduced by cuttings or grafts and classified as a new variety. Sometimes a variety will throw a number of sports which in turn may try to revert to the original plant. Golden privet is a well known sport or mutation from the original green privet, and we have all seen golden privet hedges with splashes of green foliage where the plant has reverted; these must be cut out or else they will completely take over. The same applies to hibiscus; if the original plant is strong and vigorous, then the mutation, if it reverts, may disappear. `Mrs Andreasen' is a well known sport of `Mrs George Davis' ('Kona'), and quite often the strong `Mrs George Davis' will come through and try to dominate the `Mrs Andreasen'. On this particular variety it looks very spectacular when the plant is covered with masses of double pink (`Mrs George Davis') and light apricot (`Mrs Andreasen') blooms. This plant has been known as `Peaches and Cream' when this happens, but if allowed to grow, the `Mrs George Davis' will completely outgrow and smother the `Mrs Andreasen'. 'Sabrina' is a sport of `Mrs George Davis' also, and 'Enid Lewis' is a sport of 'Sabrina'; in all we have three worthwhile sports that originated from `Mrs George Davis'.

Do not confuse the shoots or branches of understock or rootstock which arise from below the graft on grafted plants with sports. The foliage of rootstock is usually quite different from the top portion of the plant. If any of these branches appear from below the graft cut them off immediately as close as you can to the main trunk of the plant.

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