INTRODUCTION

Vertical gardens are defined as gardens that cover the facade walls using various plants species (Rahman et al., 2019). They are also called green space walls, wall gardens, green wall technologies, green scaffolding, bio walls, green façades, vertical or living walls, biofacade walls, etc., across various regions around the globe (Bakar et al., 2013, Amir et al., 2014, Rahman et al., 2014, Jim, 2015, Basher et al., 2016). Globally, more people live in urban areas than in rural areas, with 54% of the world’s population residing in urban areas (Zaid et al., 2018) its benefits, its carbon sequestration potential and its calculation methodologies, and its potential for urban heat island (UHI. Urban growth, including human population and buildings, is predicted to increase exponentially in the coming years (Peschardt and Stigsdotter, 2013, Price et al., 2015).  Urban areas will face several new and ongoing challenges related to health, environment, economy, food, education, etc (Skelhorn et al., 2014) one strategy that has been suggested to address both adaptation and mitigation for urban areas is the increased use of greenspace. A number of studies have analysed this strategy through the use of empirical, analytical methods, or numerical methods. These tend to focus on city or regional scale changes in land use with only a broad categorisation of greenspace type. This study tests seven greenspace scenarios that might be applied at a block or neighbourhood level and the resulting microclimate changes that can be achieved through such applications for a temperate city in northwest England. Using a suburban commercial site in Manchester, UK as the case study area, the research utilises the urban microclimate model ENVI-met to compare the changes in air and surface temperatures on a warm summer day in July 2010 (approximately 4. °C above the rural reference July average maximum temperature. Thus, with rapid urbanization, a need arises to allow nature to manifest in urban buildings. This rapid urbanization is hence, creating a huge potential in green space and a more quality green landscape. Urban landscaping is gaining popularity nowadays as people are becoming more conscious about a green and clean environment and are increasingly used to improve green cover in urban environment (Akbari et al., 2001, Strohbach et al., 2012, Yang et al., 2008). Urban green spaces improve the surroundings and enhance the wellbeing of urban population by positively improving the ambient conditions and noise levels thereby enhancing human health (Ghazalli et al., 2019). Apart from this, they can contribute to urban biodiversity (Lundholm, 2006, Francis and Lorimer, 2011), storm water management (Schmidt, 2003), air quality (Bruseet al., 1999, Pugh et al., 2012), temperature reduction (Santamouris, 2014) and reducing heat island effect (Alexandri and Jones, 2008, Gago et al., 2013).

The application of vertical gardening also has social and economic benefits along with environmental benefits. These systems have a therapeutic effect by promoting the mental wellbeing through exposure to vegetation, beautification of cities (Theodoridou et al., 2012), increasing the value of properties (Ichihara and Cohen, 2011) and providing heat (Sadineni et al., 2011) and noise protection (Wong et al., 2010, Renterghem et al., 2013). The demand for vertical gardens is already higher in cities but the cost and sustainability of plant species restrict the growth of vertical garden industry. The low survival and success rates of plants in green walls are due to extreme conditions such as high radiation, temperature, wind and pollution prevailing in the cities. Many enthusiastic people have started constructing vertical gardens but failed due to the lack of information on structures, suitable plant species, water and nutrient management, medium, diseases and pest management, etc. Safety concerns of supporting structures, green building ratings, innovative materials and development of various types of green modules units, community expectancy and ways and means of localizing vertical greening, reuse of construction fences, water supply and drainage system, recurring maintenance, etc., are some of the important issues that have to be addressed before proceeding with vertical gardening (Peng et al., 2015). An interdisciplinary approach involving civil and material science engineering, law discipline, architecture and urban designs is required to reduce the risks and negatives associated with vertical gardening. Since this is an upcoming area and there is very meagre research work has been carried out on this aspect with regard to India, the present investigation was carried out to find suitable ornamental flowering plants for vertical gardening during the summer season.

MATERIALS AND METHODS

The present study was conducted during 2019–2020 at the College of Horticulture, Pune, Maharashtra, India which is situatedat18.32°N latitude and 73.51°E longitude at an altitude of 555.74 MSL. The total annual rainfall is 1071.7 mm and the temperature ranges between 20.8°C and 37.6°C. 20 species of ornamental flowering plants, representing a wide spectrum of morphological variability were selected for the study (Table 1). An iron stand of 6×6 ft. was prepared and on each stand polypropylene vertical panel frames were fixed. One polypropylene vertical panel frame contains three cups with a pot locking system and on each stand, 11 columns and 3 rows of polypropylene vertical panel frames can be accommodated. One stand accommodates 4 treatments separated by planting border plants with 20 plant units per treatment. The experiment was conducted in a completely randomized design with 20 treatments and 2 replications.

Table 1: Ornamental flowering plants used for the study

2.1.  Frame description

• Dimension of 1 frame (approx.): 450×150 (Length× Width) in mm

• The area covered per set/frame is 0.73 sq. (approx.)

• The frame can be stacked vertically and horizontally

2.2.  Media

For raising a vertical garden, the selected media should be light weight, porous and neutral in pH with high water and nutrient holding capacity. Therefore, a mixture of coco peat, red soil and vermin compost in a 2:1:1/2 ratio was used as growing media.

2.3.  Consumer acceptance

The consumer acceptance was recorded for flowering plant species based on overall visual appearance considering the five parameters 1 Plant height; 2 Area coverage; 3 Number of flowers; 4 Size of flower; 5Colour of flower and thus plants are categorized into excellent, very good, good and poor. Consumer acceptance is presented in Table 10.

RESULTS AND DISCUSSION

The flowering species selected for the study were having distinctive growth habits. The data of different quantitative parameters were recorded at 20 days intervals up to 100 DAT which showed a significant variation. Plant height is an imperative trait for the existence of vertical gardens and has always been negatively correlated. The least plant height 7.3 cm and 10.1 cm was found in Crossandra infundibuliformis at 20 and 40 DAT, respectively. At 60, 80 and 90 DAT the lowest plant height was found in Begonia sppi.e.12.9, 14.4 and 15.9, respectively. The highest plant height, 24.7 cm, 36.4 and 37.6 cm was observed in Cosmos bipinnatus at 20, 40 and 60 DAT, respectively. At 80 DAT, the highest plant height 31.6 cm was observed in Salvia officinalis and Pentas lanceolata andat 100 DAT maximum plant height of 36.1 cm was recorded in Callistephus chinensis (Table 2).

Table 2: Plant height of ornamental flowering plants (summer season) (cm)

Among the treatments, wide variation was observed in plant height and it might be due to its growth habit. Based on these aspects, ornamental species like Begonia spp., Crossandra infundibuliformis, Tagetespatula and Gomphrena globose were found to be suitable for vertical gardening in summer season. The results are in line with Srikanth (2015) who found that the use of dwarf plant species was preferable for vertical gardens. Sachs et al. (1976) and Motos and Oleveira (1998) recommended the optimum plant height of a potted plant should be 1.5 to 2 times the container height.

Like any other character, the stem diameter is also equally significant as it sustains the plants from breaking and damage. Callistephus chinensis showed an increasing trend throughout the experiment (6.1 to 6.7 mm) from 20 to 100 DAT. The lowest stem diameter of 3 mm, 3.3 mm, 3.6 mm, 3.6 mm and 3.8 mm was observed in Catharanthus roseus at 20, 40, 60, 80 and 100 DAT, respectively (Table 3).

Table 3: Stem diameter of ornamental flowering plants (mm) (summer season)

The treatments exposed wide distinction in plant area coverage and it might be due to its growth habit, leaf length, leaf width and leaf area which are the main indicators to understand the plant area coverage. Based on the statistical observations, the highest area coverage (152.44 cm² and 195.2 cm²) was observed in Dianthus caryophyllus whereas; the least area coverage (32.85 cm² and 49.49 cm²) was recorded in Crossandra infundibuliformis at 20 and 40 DAT, respectively. While at 60 and 80 DAT, the highest area coverage (277.07 cm² and 290.16 cm²) was observed in Petunia×atkinsiana and the lowest area coverage was recorded in Lantana camara (82.16 cm² and 102.69 cm²), respectively (Table 4).

Table 4: Area coverage of ornamental flowering plants (cm2) (summer season)

Based on the results, ornamental species like Dianthus caryophyllus, Petunia atkinsiana, Portulaca grandiflora and  Pentas lanceolata were found to be suitable for vertical gardening in summer season. The results are in line with Srikanth (2015) and Alex (2012). The sustainability and greenery of vertical gardens depend on the number of leaves and leaf area. The number of leaves differs from species to species and it depends on the number of branches and leaf type. The results are in line with Srikanth (2015). The highest number of leaves was recorded in Portulaca grandiflora (136, 215, 258, 300 and 334) at 20, 40, 60, 80 and 100 DAT, respectively (Table 5). Among 20 plant species, only Antirrhinum majus showed the maximum number of branches (9) for summer season. At 40, 60, 80 and 100 DAT, the maximum number of branches were recorded in Portulaca grandiflora (20, 33, 33and 34) during summer season (Table 6). Significant difference with respect to the number of flowers among the 20 plant species was observed. Among them, Pentas lanceolata showed the highest number of flowers (30, 26, 40 and 37) at 40, 60, 80 and 100 DAT, respectively. Flower size is also an important character to be considered as it determines the compactness and appearance of the plant. Celosia cristata had the highest flower size (6.1 cm and 6.1 cm) at 40 and 60 DAT, respectively, while Petunia ×atkinsiana showed the highest flower size (5.3 cm and 5.4 cm) at 80 and 100 DAT, respectively (Table 7). The lowest flower size (1.3, 1.3, 1.4 and 1.6 cm) was observed in Gomphrena globosa at 40, 60, 80 and 100 DAT, respectively (Table 8).

Table 5: Number of leaves of ornamental flowering plants

Table 6: Number of branches of ornamental flowering plants (summer season)

Table 7: Number of flowers of ornamental flowering plants (summer season)

Table 8: Size of flowers of ornamental flowering plant (summer season)

During the course of its growing period, momentous differences were observed among the 20 species in the days required for flower initiation. In the present study, it was observed that Tagetes patula required the least number of days for flower initiation i.e. 19.2 days. While the highest number of days was recorded in Portulaca grandiflora (51.5 days) (Table 9). Species with early flower initiation are desired for the maintenance of aesthetic beauty of vertical garden. Early initiation of flower may be due to genetic factors and prevailing climatic conditions of the area. Significant differences were observed among the 20 species for days required for flowering. Species with the maximum duration of flowering are the most desirable flowering plants for vertical gardens. In the present study, Begonia spp(72.5 days) recorded the highest flowering duration, which was found at par with Catharanthus roseus (72.0 days), Antirrhinum majus (70.5 days) and Gomphrena globosa (68 days). The lowest flowering duration was observed in Cosmos bipinnatus (27.5 days) (Table 9). The most important aspect of vertical garden is the degree of time in which the plants appears healthy and attractive. Thus, the plants with longer durations are the most preferred for vertical gardens.

In the present study, significant differences were observed among the 20 species for total cropping duration out of which, Antirrhinum majus recorded the highest crop duration of 130.5 days which was found at par with Gazania linearis (121 days) and Pentas lanceolata (120 days). The lowest crop duration was observed in Celosia cristata (75 days) (Table 9). Significant differences were observed among the 20 species for its establishment percentage.

The present investigation witnessed a 100% faster establishment in 12 species under study. The highest establishment percent was observed in Antirrhinum majus, Begonia spp, Calendula officinalis, Crossandra infundibuliformis, Dianthus caryophyllus, Lantana camara, Pentas lanceolata, Portulaca grandiflora, Salvia officinalis, Catharanthus roseus, Torenia fournieri and Gomphrena globosa. While the species Cosmos bipinnatus, and Petunia ×atkinsiana showed minimum survival percentage (Table 9). This is due to its capacity to withstand adverse conditions like increase in temperature, wind velocity and its potential to tolerate drought conditions which is a prime expectation in any vertical garden plant selection. The findings are in line with Srikanth (2015).

Table 9: Flower initiation (days), Flower duration (days), Crop duration (days), Establishment (survival %) of ornamental flowering plants (summer season)

Table 10: Consumer Acceptance

3.1.  Qualitative characters

Flower colour, growth habit, leaf type and leaf shape were taken as qualitative characteristics as they helped to relate to the aesthetic value of the plants. All the qualitative characters were presented in Table 11.

3.2.  Flower colour

Flower colour is one of the factors to enhance the attractiveness of plants. The flower colour was recorded by comparing the colour of the flower with the Royal Horticulture Society colour chart (5th edition). Appearance and attractiveness are important factors in the study of flowering plants. The attractiveness depends on the colour of flower plants. Among these 20 species, significant difference was observed.

3.3.  Growth habit

Among the 20 plant species, significant difference was observed in the growth habit. Antirrhinum majus, Zinnia elegans, Lantana camara, Pentas lanceolata, Catharanthus roseus were having erect and branching types. Celosia cristata, Cosmos bipinnatusand Salvia officinalis were having erect and non-branching types. Begonia spp, Dianthus caryophyllus, Tagetespatula, Viola tricolor var. hortensis, Petunia×atkinsiana, Torenia fournieri and Gomphrenag lobosa were of spreading and branching types. Callistephus chinensis, Calendula officinalis, Crossandra infundibuliformis and Gazania linearis were of spreading and non-branching types.

3.4.  Leaf type

Among these 20 plant species, only Tagetes patula is odd pinnately compound and other remaining 19 species were recorded as simple type of leaf.

3.5.  Leaf shape

Among the 20 plant species, difference was observed in the leaf shape. Begonia spp, Calendula officinalis, Zinnia elegans, Lantana camara, Viola tricolorvar. hortensis and Catharanthus roseus has ovate leaf shape. Antirrhinum majus, Dianthus caryophyllus, Tagetes patula, Torenia fournieri, Gomphrena globosa, Pentas lanceolata were observed to have oblong leaf shapes. Gazania linearis, Petunia×atkinsiana, was found to have linear type of leaf shape. Callistephus chinensis was observed to have spatulate type of leaf shape. Celosia cristata was recorded as saggitate type of leaf shape and Cosmos bipinnatus was found to have variable type of leaf shape and Crossandra infundibuliformis and Portulaca grandiflora as ovate to lanceolate type of leaf shape.

Table 11: Qualitative leaf characters of flowering plants selected for the study

Table 11: Continue...

CONCLUSION

The study of evaluation of 20 flowering plant species in the summer season concluded that the ornamental flowering plant viz., Begonia spp., Dianthus caryophyllus, Torenia fournieri, Gomphrena globosa and Catharanthus roseus were found to be excellent for the summer season.

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