Growing stages of ornamental plants

The mastery of growing stages is crucial for the adequate application of growth regulation. The development of the higher plants is divisible for two separate periods: for the juvenile (or vegetative) and for the adult (or generative) stage. The main difference between the two stages that the plants are not able to bloom in juvenile phase. It may be further peculiarity of the juvenile stage the differing leaf-form (heterophylly), the differing growing character (inclination for tillering and sprouting, or raising of creeping stems on the ground), and the more effective protection against the harmful animals (thorns, prickles, stinging-marginal leaves, foliage high in repellent fragrance). The tissue-conformation of the plants is also differed in the juvenile stage compare to the latter stadium. The stem of a juvenile plant has as usual flimsier and more parenchymatic tissue. Therefore the adventitious roots can initiate easier, so the vegetative propagation becomes faster. Contrarily while the adult phase the plants attain their whole advance state, and they are already able to grow flowers and fruits, if the environmental conditions are suitable for there. The other characteristics of the adult stage may be the changed leaf-form and growing character (non-tillering, non-sprouting, soft-growing), the loosing of the protection organs, and in the stem the stereome dominates against the parenchymatic tissues, so the regeneration ability of the plant decreases.

The two phases follow each other every time, but the transition can drag for years, especially in woody plants. This procedure takes only few weeks or months in the herbaceous plants and short-life species.

The transition is affected by more factors; the most important is the plant-size. It can be specified also in absolute unit (e.g. in the case of bulbous plants, where the adult age can be defined by the diameter of the bulbs), but in the most cases the absolute volumetric sizes are not object, but the number of internodes and leaves. It can be so possible, that the plant, which was treated by internode-extension inhibitor (growth retardant), is able to bloom. The conformation of growing stages is also influenced by the water- and nutrient-supply of the plant. The vegetative organs of a well or too much supplied plant growths significantly, so the juvenile phase elongates. First of all nitrogen generates this effect, while the dominant potassium and phosphorus push the plant development to generative direction. The stinting of nutrient and irrigation induces the early ageing of plant organism, and it also means that the plant comes faster into production. This phenomenon called neoteny is a defensive mechanism in the life of the plant, because it tries to ensure by any means the advanced reproduction.

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Juvenile and adult leafs of Hedera helix

Juvenile and adult leafs of Morus alba

3. Growth regulation of ornamental plants

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Juvenile, transitional and adult leafs of Monstera deliciosa

But the reduced supply worsens the quality of flowering, so it has to be carefully with the using of this blooming induction method. It has to find the point where the decreased supply causes only a minimal blooming quality-loss. Therefore, the plant gets abundant supply again after the induction of generative phase, because after a successful induction the plant does not return easily to vegetative stage.

However, there are some cases when the backspace to the juvenile phase can be stimulated, it called rejuvenilization. Of the vegetative propagation the cuttings and what is more the grafting have also rejuvenilization effect. The hormonal balance changes in the cuttings after the isolation from the mother-plant, and they come back again more or less into juvenile stage. In the case of grafting due to the juvenile rootstock the scion becomes also juvenile again. But this phenomenon may depend strongly on species and varieties. Sometimes the plant does not return to juvenile phase after vegetative propagation. This knowledge is exploited by the horticulturists, e.g. in the case of ‟Arborescens‟ type

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ivies where the aim is the preservation of the adult attributes on the propagated plant, too. The stronger and most safety rejuvenilization effect can be realized by external given hormones (cytokinins), which are commonly used also in micropropagation. There can be observed on woody plants, that it is on the same specimen juvenile and adult parts, too. It is due to the inequality of the light distribution. The marginal part of the crown, which has a lot of light, becomes faster adult compare to the overshadowed, lower part of the crown. This shoots in the shadow retain their juvenile form for a longer time, which advantage is taken of by the horticulturists, and they collect the cuttings from this part of the plant. So, the conformation of growing stages is a complex system in the plants which depends on more factors.

The changing to adult phase does not mean automatically the starting of the flower-induction. It eventuates, if the adequate environmental conditions are realized, which will discussed at large in the next subsection.