Rose can be grown successfully in different climatic zones. However, moderate temperature, bright sunshine and high light intensities are good for flower production. The early morning sun should beam over the rose beds for at least six hours a day. Rose bushes not receiving the morning sun perform poorly. In hot weather, however, partial shade during the afternoon when the sun is hot is beneficial. An area protected from hot and cold blast of wind is ideal. In England, Canada, northern United States of America, Germany and Denmark large number of young' plants as well as established plants are lost because of low temperature in winters.
The Pernetianas are most subject to loss by freezing. In cold parts of Europe and USA many rose growers protect their plants for over six months each year by elaborate and costly methods. In subtropical climates plants do not get true rest period and lose their virility within a few years. Under tropical conditions very high quality-roses can be grown. Most rose breeding is directed to meet the requirements of the temperate climate. In areas of low rainfall and high summer temperatures, dwarf roses are best.
The climatic conditions that prevail in different parts of India are well suited to rose cultivation. In the northern plains, roses flower best during winter, whereas in the temperate hilly regions of the Himalayas, the best rose flowers are produced in summer. The place like Pune, Nasik and Sangri, in the western part of India; and Bangalore in Southern India have excellent agro-climatic conditions for rose growing. The plains of Eastern India are also suitable for cultivation of many cultivars of roses.
Light intensity is the most important factor affecting the growth of rose plant and flowering. Decrease in light intensity and the duration of light period owing to the seasonal changes or shading reduce the yield of roses. Supplementary lighting or relatively high levels of irradiance, especially during periods of low solar radiation, results in increasing number of flowers. Total plant weight, growth of plant and flower production reduces with the low light intensity in roses.
Colour of the flower is influenced by light intensity and high light intensity is necessary for anthocyanin formation in rose cultivars. The effect of light on bud sprouting is related mainly to red: far-redratio; while the effect of flower development is related to mainly photon flux density. The duration of light has also pronounced effect on vegetative growth as well as reproductive structure.
Various workers extensively investigated the possible use of supplementary lighting with relatively high levels of irradiance in order to increase the productivity of green house rose. Seasonal fluctuations of solar radiation affects the rose flower production. Flower bud abortion in rose is affected by low light intensity at early stages of shoot development. Nearly 50 to 60 days are required to develop a flowering shoot from bud sprouting until flower harvest. Shading, which is widely used in order to reduce the rise in green house temperature during summer month, frequently results in decrease in flower yield. Generally, stems of the summer flowers are shorter, thinner and have smaller leaves and flower buds with flower petals than winter flowers.
Photosynthesis of roses is influenced by light intensity and affected by leaf age, CO2 levels, temperature, cultivar and water status of plants. Decrease in light intensity was followed by a decrease in the activity of gibberellin-like substances in the uppermost shoot of the rose stem. This decrease was more pronounced in the lower shoots, which are more prone to flower abortion. Darkening of rose shoot tip reduced its sink strength, while application of BA to the darkened shoot restored the mobilization capacity of the sink. The contents of endogenous cytokinins in the darkened shoots were lighter than the shoots exposed to light, indicating that the darkening may cause inactivation of endogenous cytokinins.
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1. Some rose species need special pruning
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