Influence of Plant Spacing on Growth, Phenology, and Calyx Yield of Roselle (Hibiscus sabdariffa L.) under Subtropical Conditions

Roselle (Hibiscus sabdariffa) is a tropical tetraploid (2n=72) annual crop of the Malvaceae family, originating in West Africa and now widely grown across tropical and subtropical regions (Jamini et al., 2019; Omenna et al., 2023). More than 300 species of roselle have been grown throughout the southern United States, Mexico, Central America, and the West Indies (Jadhav et al., 2025). Major producing countries include Nigeria, Sudan, Thailand, and India, with yields ranging from 1.5–3 t/ha (El-Naim et al., 2012). Roselle is popularly known as ‘mesta’ or ‘chukur’ in the Indian subcontinent, including Bangladesh. It grows in warm climates and produces yellow flowers with crimson calyces rich in “anthocyanins” (Basazinew Degu & Bizuayehu Tesfaye, 2016). Calyx is used in various foods and herbal beverages due to its high antioxidant content, nutrients, low in calories, and offers several health benefits, including anti-hypertensive and anti-cancer properties (Thimmaiah et al., 2024). The crop is rich in protein (1.5%), fibre, calcium, iron, carotenes, vitamin C, phenolics, and sugars (6–8%), contributing to antimicrobial activity, diabetes control, reduced blood pressure (7–10 mmHg), lower cholesterol (10–15%), and anaemia prevention through folate-rich leaves (El-Sagher et al., 2024; Gebremedin, 2015; Hopkins et al., 2013).

Despite its economic potential, roselle agronomic practices are largely optimized for fibre rather than calyx yield. Plant spacing plays a critical role in regulating growth, light interception, nutrient uptake, LAI development, and photosynthetic efficiency, ultimately influencing biomass and yield (Gebremedin, 2015; Paul et al., 2018; Nazifi et al., 2024). Many growers continue to use narrow spacing suitable for fibre production, even though wider spacing is often more favourable for calyx yield. Density affects growth traits such as plant height, leaf number, branching, and flower production, and interacts strongly with nutrient management (Inuwa et al., 2022; Mendoza-Pérez et al., 2024). Although closer spacing increases calyces per plant, intermediate spacing consistently produces the highest calyx yield per hectare by balancing individual plant performance and population productivity (Bako, 2025; El-Naim et al., 2012). 

Although roselle has been widely studied, spacing recommendations still vary due to differences in genotype, environment, and management practices. Since plant density plays a key role in shaping growth, flowering, and yield, this study examined how different spacing levels affect roselle phenology, growth, and calyx yield in Bangladesh, where local information remains limited.

Description of the Experimental Site

The experiment was carried out at the Agronomy Field Laboratory of Bangladesh Agricultural University in Mymensingh from July 2023 to February 2024. The site (24 ° 75' N, 90 ° 50' E; 18 m elevation) lies in the Old Brahmaputra Floodplain (AEZ-9) with Sonatala series dark grey floodplain soil. The area is situated in a sub-tropical climate with heavy precipitation from April to October, and minimal rainfall from October to March.

Figure 1: Monthly average temperature, rainfall, relative humidity, and sunshine (hr) during the experimental period

Experimental Treatments, Design and Layout

The experiment comprised seven spacing treatments viz., viz., 30 cm × 30 cm (S₁), 60 cm × 30 cm (S₂), 60 cm × 45 cm (S₃), 60 cm × 60 cm (S₄), 90 cm × 30 cm (S₅), 90 cm × 45 cm (S₆), and 90 cm × 60 cm (S₇). The experiment followed a Randomized Complete Block Design with three replications. Each 6.0 m × 4.5 m plot (27.0 m²) contained seven treatments, randomly assigned, for a total of 21 plots. A spacing of 0.75 m between replications and 0.50 m between plots was maintained.

Planting material

The roselle variety, namely, BJRI VM-1 (Mesta-2), was used in the experiment. The seeds of these varieties were collected from the Bangladesh Jute Research Institute. BJRI VM-1 (Mesta-2) is a widely adaptable, disease-resistant, high-yielding, early maturing variety with a robust growth habit.

Cultural operations

The field was prepared with two ploughings and laddering, subsequently levelled and cleared of all weeds and residues. The land was prepared, and the layout of the plots was finalised on 26 July 2023, in accordance with the experimental design. Fertilisers were applied at 70 kg ha⁻¹ N, 20 kg ha⁻¹ P, 40 kg ha⁻¹ K, and 3.5 kg ha⁻¹ Zn, utilising urea, TSP, MoP, and zinc sulphate. One-third of the nitrogen and all other fertilisers were incorporated during the final land preparation, while the remaining nitrogen was applied at 30 and 60 DAS. Seeds were sown on 27 July 2023 according to the treatment, with three seeds planted in hill^-1.

Intercultural operations

Two hand weedings were done at 30 and 50 DAS. Thinning was done to keep one healthy seedling per hill at 30 days following seeding, and any spaces were replaced. The monsoon rains eliminated the need for additional irrigation, although drainage was installed to prevent waterlogging. Sevin 85SP was applied at 1.7 kg per acre to control mealybug infestations.

Sampling, Harvesting, and Processing

Data on 50% flowering were recorded on 30 November 2023. Four randomly selected plants (excluding border plants) were uprooted from each unit plot for plant characterisation and 90% physiological maturity. Red or crimson, firm calyces, fading flowers, enlarged calyces and drying seed pods identified maturity. Harvesting was carried out on 30 January 2024 from a 180 cm × 180 cm area at the centre of each plot. The harvested samples were tagged and transported to the Agronomy Field Laboratory threshing floor. Calyces were separated using a sharp knife, and seed pods were removed with a coring tool.

Data Collection

For data collection, five plants were randomly selected from each plot, and observations were recorded on vegetative growth, yield, and quality-related traits. The collected data included phenological parameters such as days to 50% flower bud appearance, 50% flowering, and 90% physiological maturity. At 50% flowering, plant height, number of main branches, number of leaves, leaf area index, leaf weight, petiole length, petiole weight, and stem weight were measured. At 90% physiological maturity, the number of fruits per plant, fruit length, fruit weight, and calyx weight were recorded. At harvest, biological yield, fruit yield, calyx yield, and seed yield were obtained.

Procedure for Leaf Area Index (LAI) data collection

The ground area occupied by each plant, based on the spacing in the plot, was determined, and the leaf area index was calculated using the following formula:

LAI =

Statistical Analysis

The data were examined using the Analysis of Variance (ANOVA) method, employing the statistical software packages Statistix-10 and R. Subsequently, mean differences were assessed using the Least Significant Difference (LSD) test.

Phenological Characteristics

Number of days from sowing to 50% budding

The number of days from sowing to 50% budding varied widely among different spacings. The highest number of days from sowing to 50% budding was observed in S₄ (103), and the lowest number of days (101) in S₁ (Table 1). Closer spacing led to a faster transition to 50% budding in roselle plants compared to wider spacings, likely due to increased competition for light and resources, which accelerated early development, whereas wider spacings allowed slower but more robust vegetative growth (Kaur et al., 2024).

Number of days from sowing to 50% flowering

Spacing clearly affected flowering time. The highest number of days (116.67) was observed with S_1, and the lowest number of days (115) was observed with S₇ (Table 1). Wider spacing enhanced light penetration and air circulation within the canopy, promoting healthier plant growth and contributing to faster flowering (Talpur et al., 2023).

Number of days from sowing to 90% maturity

Spacing clearly influenced how quickly the plants matured. Plants in S₁ took the longest to reach 90% maturity (154 days), while the widest spacing (S₇) matured earliest (148 days), similar to S₄ (Table 1). Wider spacing allowed plants to reach maturity faster than the closest spacing, due to reduced competition for light, water, and nutrients (Pokhrel et al., 2023).

             Table 1. Effect of spacing on phenological characteristics of roselle

In a column, the figures with the same letter(s) or without letter do not differ significantly, whereas figures with dissimilar letter(s) differ significantly. *= Significant at 5% level of probability, *** = Significant at 0.1% level of probability.

Growth parameters

Plant height

Different spacings significantly influenced plant height. The highest plant height (196.87 cm) was found with S₇. The lowest plant height (155.59 cm) was found with S₁ (Table 2). Due to less competition and better access to light, water, and nutrients, roselle plants spaced 50 × 50 cm grew higher than those spaced 30 × 30 cm (Bako, 2025)

Number of main branches plant^-1

Spacing affected the number of main branches per plant, with the highest (14.33) at S₇ and the lowest (6.00) at S₁ (Table 2). Roselle plants spaced 60 cm apart had more main branches than those at 30 cm, due to reduced competition, allowing bushier growth (Mendoza-Pérez et al., 2024).

Number of leaves plant^-1

The number of leaves per plant varied with spacing: S7 had the most (134.22), comparable to S4 and S6, and S1 had the fewest (105.00), followed by S2 (Table 2). Reducing plant density or increasing spacing allows each roselle plant to grow more vigorously, leading to enhanced leaf production (Ado et al., 2015).

Leaf area index

Different spacings have a considerable impact on the leaf area index. The highest leaf area index (6.82) was found with S_1. The lowest leaf area index (1.52) was found with S₇ (Table 2). Roselle plants spaced at 30 cm exhibited a higher leaf area index than those at 50 cm, indicating that closer spacing increases leaf density and canopy coverage. However, excessively close spacing may lead to greater competition for light, water, and nutrients, potentially limiting overall plant growth and yield. Optimal spacing, therefore, is essential to balance leaf development with resource availability for healthier, more productive plants (Khan & Islam, 2023; Zuo et al., 2024).

Weight of leaves plant^-1

Different spacings significantly influenced the weight of leaves plant^-1. The highest weight of leaves (134.99 g) was found with S_7, and the lowest weight of leaves (107.87 g) was found with S₁ (Table 2). Wider spacing reduces competition, allowing roselle plants to grow larger and produce heavier leaves. Closer spacing, on the other hand, increases competition and reduces leaf weight per plant despite higher total biomass (Muhie & Yimer, 2023).

Petiole length

Different spacings have a substantial impact on petiole length. The highest petiole length (5.91 cm) was found with S_7, and the lowest petiole length (4.67 cm) was found with S₁ (Table 2). Plants grown with wider spacing had longer petioles, as reduced competition allows more resources to be directed toward vegetative growth, including petiole elongation (Khattak et al., 2016).

Weight of petioles plant^-1

Different spacings significantly influenced the weight of petioles plant^-1. The heaviest petioles (24.41 g) were found with S₇. The lowest petiole weight (19.54 g) was observed with S₁ (Table 2). Wider spacing lets roselle plants grow bigger petioles, increasing their weight, and shows how giving plants room can boost yield in vegetative crops (Khattak et al., 2016).

Stem weight plant^-1

Stem weight plant^-1 was significantly affected by spacing. The highest stem weight (131.39 g) was found with S_7, and the lowest stem weight (84.60 g) was found with S₁ (Table 2). Optimal spacing enhances stem biomass in roselle, making wider spacing a preferred approach for maximizing stem yield (Li et al., 2025).

Table 2. Effect of spacing on growth parameters of roselle

In a column, the figures with the same letter(s) or without letter do not differ significantly, whereas figures with dissimilar letter(s) differ significantly. *= Significant at 5% level of probability, *** = Significant at 0.1% level of probability

Yield attributes

Length of fruits

Fruit length was significantly influenced by different spacings. The highest length of fruits (6.46 cm) was found with S_7, and the lowest length of fruits (4.77 cm) was found with S₁ (Table 3). Wider plant spacing, such as 60 cm, increased the length of Hibiscus sabdariffa fruits compared to denser spacing of 30 cm because of reduced inter-plant competition and improved resource availability (Ogam et al., 2024).

Weight of fruits plant^-1

Different spacings had a substantial impact on fruit weight per plant. S₇ produced the heaviest fruits (93.73 g). S₁ had the fruits with the lowest weight (58.27 g) (Table 3).  Due to increased photosynthetic efficiency and better resource availability, roselle plants grown at wider spacing yielded noticeably larger fruit weights (Talpur et al., 2023).

Weight of calyces plant^-1

Calyx weight per plant was significantly affected by spacing, with the highest value (44.00 g) recorded in S₇ and the lowest (22.22 g) in S₁ (Table 3). Because of better light access and reduced interplant competition, wider spacing increased nutrient uptake and plant growth, leading to a noticeable increase in calyx weight (ALobaidy et al., 2023).

Biological yield

Plant spacing significantly affected biological yield. S₄ had the highest value (13.87 t ha⁻¹), while S₇ had the lowest yield (8.45 t ha⁻¹) (Table 3). In roselle cultivation, a 50 × 50 cm spacing maximised plant size and population density, leading to a higher biological yield per unit area than either closer or wider spacings (Samari et al., 2023).

                Table 3. Effect of spacing on yield attributes and yield of roselle

In a column, the figures with the same letter(s) or without letter do not differ significantly, whereas figures with dissimilar letter(s) differ significantly. *= Significant at 5% level of probability, *** = Significant at 0.1% level of probability.

Number of fruits plant^-1

Different spacing treatments significantly influenced the number of fruits per plant. The highest number of mature fruits per plant (70.41) was recorded under S₇, whereas the lowest number (32.50) was observed under S₁. The maximum number of immature fruits per plant (15.83) was obtained from S₇, while the minimum number (9.58) was recorded under S₁ (Figure A). Closer spacing tends to limit branch development and fruit production per plant in Hibiscus species due to increased inter-plant competition. Roselle plants spaced 60 × 60 cm can produce more fruits than those at 30 × 30 cm, showing that giving plants enough space helps them grow stronger and produce more (Abrham & Shumbulo, 2024; Khan & Islam, 2023).

Fruit yield

Fruit yield varied significantly among spacing treatments, with the highest yield (36.77 t ha⁻¹) recorded in S₄ and the lowest (20.17 t ha⁻¹) in S₇. The highest dry fruit yield (2.25 t ha^-1) was found with S₄. The lowest dry fruit yield (1.24 t ha^-1) was found with S₇ (Figure 2-B)_. Wider plant spacing improved fruit yield and quality in roselle. The highest fresh fruit yield was achieved at 50 cm × 50 cm spacing due to reduced plant competition and more efficient use of light, water, and nutrients, which enhanced photosynthesis and fruit development (Samari et al., 2023).

Calyx yield

Calyx yields were significantly influenced by plant spacing. The highest fresh calyx yield (17.15 t ha⁻¹) and dry calyx yield (0.69 t ha⁻¹) were recorded in S₄, while the lowest fresh (9.41 t ha⁻¹) and dry (0.38 t ha⁻¹) yields were observed in S₇ (Figure 2-C). Wider plant spacing produced better yield performance depending on soil and environmental conditions. An optimal spacing of 60–75 cm maximized fresh calyx yield by balancing individual plant growth with overall field productivity, reducing competition for light, water, and nutrients, and promoting better canopy development and photosynthetic efficiency (Gebremedin, 2015; Mendoza-Pérez et al., 2024).

Seed yield

Fresh seed yield was significantly affected by spacing, with the highest yield (19.62 t ha⁻¹) in S₄ and the lowest (10.77 t ha⁻¹) in S_7. The highest dry seed yield (1.57 t ha^-1) was found with S₄. The lowest fresh seed yield (0.86 t ha^-1) was found with S₇ (Figure 2-D)_. Wider spacing optimized both individual plant performance and total seed yield per hectare, emphasizing the need to adjust spacing according to specific environmental and cultivation conditions. Roselle plants spaced at 60 × 40 cm produced higher seed yield than closer spacings, due to reduced inter-plant competition and enhanced vegetative growth (El-Sagher et al., 2024).

Figure 2. Effect of spacing on yield attribute characters of roselle (S₁ = 30 cm × 30 cm, S₂ = 60 cm × 30 cm, S₃ = 60 cm × 45 cm, S₄ = 60 cm × 60 cm, S₅ = 90 cm × 30 cm, S₆ = 90 cm × 45 cm, S₇ = 90 cm × 60 cm; Bar represents standard error)

Heatmap analysis

A heatmap was used to illustrate the relationships between growth traits and calyx yield of roselle (Hibiscus sabdariffa) under different plant spacing treatments (Figure 3). Growth and yield variables are shown on the x-axis, while spacing treatments appear on the y-axis. The heat map revealed clear differences in trait responses across spacing levels. Fresh calyx yield, fresh fruit yield, fresh seed yield, dry seed yield, days to flowering, days to maturity, and leaf area index showed higher contributions under optimum spacing, indicating favorable growth and yield performance. In contrast, plant height, calyx weight, leaf number, petiole length, leaf length, and leaf weight showed lower contributions at closer or non-optimal spacing, suggesting greater vegetative growth at the expense of yield efficiency. Overall, the heat map shows that optimal spacing improves calyx yield primarily by enabling efficient biomass accumulation and balanced structural growth, rather than excessive vegetative expansion.

Figure 3: Heatmap analysis of growth and yield traits of roselle (Hibiscus sabdariffa) under different plant spacing. ∗∗∗, ∗∗, ∗ and ns (not significant) represent probability of ≤0.001, ≤0.01, ≤0.05 and >0.05, respectively. Where, STB= No of days from sowing to 50% budding, STF= No of days from sowing to 50% flowering, STM= No of days from sowing to 90% maturity, PH= Plant height (cm), BN= Branches (plant^-1),  LN= Leaf number, LAI= Leaf area index (cm²), LW= Leaves weight (g), PL= Petiole length (cm), PW= Petioles weight (g), SW= Stem weight(g), MF= Mature fruits, IMF= Immature fruits, FL= Fruit Length (cm), FW= Fruit weight (g), CW= Calyx weight (g), BY= Biological yield, FFY= Fresh fruit yield (t ha^-1), DFY= Dry fruit yield (t ha^-1), FCY= Fresh calyx yield (t ha^-1), DCY= Dry calyx yield (t ha^-1), FSY= Fresh seed yield(t ha^-1), DSY= Dry seed yield(t ha^-1)

The study demonstrates that plant spacing significantly affects the vegetative growth, phenological development and yield attributes of roselle. Wider spacing enhances individual plant performance, such as branching, leaf number, fruit, and calyx weight plant^-1. In contrast, intermediate spacing (60 cm × 60 cm) produces the highest fruit, calyx, and seed yields per hectare. Therefore, cultivation of roselle at a spacing of 60 cm × 60 cm is suggested to maximize calyx yield and achieve sustainable productivity under Bangladesh's agro-climatic conditions.

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