Evaluation of Ornamental flowering shrubes for Tropical landscapes

Abstract

The present study entitled “Evaluation of ornamental flowering shrubs for tropical landscapes” was carried out at the Department of Pomology and Floriculture, College of Horticulture, Vellanikkara from Jan. 2011 to Dec. 2011. The objectives were to evaluate ornamental flowering shrubs for suitability to various landscaping uses and to compute Air Pollution Tolerance Index. The study involved evaluation of 30 tropical ornamental flowering shrub species or varieties. The selected shrubs were four years old, maintained in the shrubbery of the Department of Pomology and Floriculture. The experiment was laid out in CRD with three replications. Various vegetative and floral characters were recorded and data analysed and correlation studies were made with weather parameters. Shrubs selected for the study were described based on morphological characters. Growth of shrubs was measured in terms of height and spread. Based on the manageable height, they were classified into three groups, i.e. Tall (height above 2 m), Medium (height 1m- 2m) and Dwarf (height below 1m). Among the 30 shrubs evaluated, the maximum height was observed for Calliandra haematocephala (319.4 cm) and the minimum for Lonicera japonica (49.9 cm). Plant spread varied from 43.4 cm in Wrightia antidysenterica to 269.7 cm in Calliandra haematocephala. Regression equation of height for predicting spread was formulated using the monthly data on height and spread. Foliage characters like leaf length, leaf area, petiole length, girth and internodal length were measured. Based on leaf area, plants were categorized into medium coarse, medium, medium fine and fine textured. Qualitative characters of the foliage like shape of leaf, base, tip, margin and colour of leaf were observed and used for plant description as well as categorizing them into different texture classes. Shrub canopy shape (silhouette) was observed and used for making schematic diagram. Qualitative characters of flowers like type of inflorescence, position of inflorescence, colour and fragrance were observed. Time taken to open up the inflorescence from bud stage, persistence of single flower as well as the inflorescence were also observed. Quantitative characters like inflorescence diameter, single flower length and diameter and number of flowers per inflorescence were also recorded. Flowering seasons of the shrubs were observed and accordingly they were categorized into four different phenological phases i.e. Dec-Feb, Mar-May, June- Aug and Sep-Nov. Sideruns were observed and phenological configurations were made. Air Pollution Tolerance Indices of the shrubs were calculated. Calliandra haematocephala (31.7) showed the highest APTI value and the minimum value was observed for Allamanda cathartica ‘Dwarf’ (9.2). Shrubs were categorized into sensitive (value ≤14), intermediate (15- 19), medium tolerant (20-24) and tolerant (> 24) groups based on their APTI values. Based on the different characters studied, shrubs were classified into different landscape utility groups such as, accent plant, foundation planting, screening and privacy, hedges and topiary, shrub border, background planting, corner planting, Shrub group and mass planting, Pot and Container planting, fragrant garden, moon garden, xeriscaping, rock garden, covering sloppy banks and butterfly garden. Shrubs were observed for pest and disease incidence. Major pests were leaf eating caterpillars in Mussaenda erythropylla, Nerium indicum, Calliandra haematocephala and Ixora coccinea, flower bud borer in Wrightia antidysenterica, mealy bug and scales. Shrubs were not severely affected by diseases. Minor leaf spots were observed in certain shrubs. In the present study, shrubs were recommended for various functional uses in the landscapes based on their growth, flowering and morphological characters. Based on flowering season, they were categorized into four phenological phases. Side-runs were observed and phenological configurations were made. Air Pollution Tolerance Indices of the shrubs were also computed and the plants were categorized according to their APTI values.