Evaluation of Quality Performance in Paper Pulp vs. Polyethylene Nursery Pots for Green Sustainability

Abstract

The use of biodegradable paper pulp pots has been gaining traction, especially among environmentally conscious consumers and horticultural practitioners who prioritize sustainability. The choice between paper pulp and polyethylene nursery pots in horticultural practices is a complex decision, involving considerations such as environmental impact, cost-effectiveness, durability, and overall sustainability. This study aims to provide practical insights into the comparative performance of paper pulp and polyethylene pots, specifically in terms of plant health, degradation, and techno-economic considerations. The study involved the growth performance assessment of four plant species, Cannonball Tomato, Celebrity Tomato, Parris Island Lettuce, and French Marigold, in a greenhouse experiment setup. Additionally, a degradation analysis was conducted to determine the average degradation rate and pattern. Finally, a techno-economic analysis compared the value of plant health and degradation with the market price. By evaluating the quality performance aspects of paper pulp pots, this study not only provides valuable insights but also identifies potential areas of improvement for other biodegradable pots, thereby contributing to the ongoing efforts to promote sustainable horticultural practices.

1. Introduction

In 2021, the United States (US) generated approximately 40 million metric tons of plastic waste [1], with only around 5–6% being recycled due to challenges like soil and pesticide contamination, along with ultraviolet photodegradation, especially impacting agricultural products like polyethylene or plastic garden pots [2]. These polyethylene pots, predominantly made from petroleum-based plastics for their affordability, durability, and flexibility, face significant recycling hurdles due to contamination, contributing to the environmental crisis with an estimated 98% ending up in landfills, posing long-term risks as they can take thousands of years to decompose, releasing toxic chemicals into soil, groundwater, and food supplies as they degrade [3]. Furthermore, paper and paperboard waste constitutes a significant portion of the total municipal solid waste (MSW) produced in the US, amounting to 68.05 million tons, and ranks as the third largest component of MSW disposed of in landfills [4]. Both paper and plastic have significant manufacturing-related costs and environmental impacts, but they differ in terms of raw material sources, energy consumption, and end-of-life environmental effects. Paper production is resource-intensive, consuming considerable energy and water and generating substantial waste and greenhouse gases. Despite this, paper is derived from renewable resources, unlike plastic, which originates from the limited resource of oil—though plastics account for only 4% of fossil resource use and have lower energy and water requirements [5]. Paper’s weight and volume also add to transportation costs. This makes polyethylene production more cost-effective. In terms of recycling, the Environmental Protection Agency (EPA) notes that paper is more likely to be recycled (about two-thirds) compared to plastic (5%) and is also more manageable in recycling facilities due to its lower contamination sensitivity [6].

In a move towards sustainability, integrating solid waste into the production chain can aid the circular economy’s objective of fostering environmentally friendly and sustainable systems and industrial processes. Planting pots manufactured from industrial and agricultural waste like wood pulp and paper can either be planted directly into the soil along with the plant, where they will decompose over time, or, in some cases, must be disposed of after transplantation into a compost or landfill facility where they will biodegrade. This approach promotes both environmental friendliness and sustainability in production practices. An instance of these paper pots in practice is the pots produced by Western Pulp Products in Oregon, USA. These pots are composed of recycled paper, with over 74% being recycled material, including at least 37% post-consumer recycled paper, along with pressed wood pulp [7].

Paper pulp pots have been utilized across various contexts and applications—as summarized in

Table 1. Summary of significant research highlights and findings related to paper pots.

Refs.	Research Highlights	Results
Section A. Research on paper pulp pots manufacturing-related characteristics
Juanga-Labayen and Yuan [8]	Investigated the effectiveness of blending textile waste with paper waste to create biodegradable seedling pots, demonstrating comparable strength and biodegradability to commercial alternatives.	The bio-composite blend, consisting of cotton and polycotton with newspaper and corrugated cardboard, exhibited optimal mechanical properties and anaerobic biodegradability while achieving 100% seed germination, highlighting its potential as an environmentally friendly alternative.
Paudel et al. [9]	Investigated the properties of paper-based seedling pots with varying additives in pot production.	Results indicated that while water absorption and tensile strength differed among the pots, additives improved pot strength in wet conditions without affecting seedling germination and growth.
Lee et al. [10]	Developed a biodegradable seedling pot by blending paper mill sludge with old newspaper at varying ratios, resulting in rapid organic matter deterioration due to a low carbon-to-nitrogen (C:N) ratio below 20.	Increasing paper content enhanced pot thickness and decreased pot density, while cellulose fibers in paper facilitated water absorption, with the addition of alkyl ketene dimer (AKD) aiding in water repellency during seedling growth. Incorporating wet strength additives improved breaking length and burst strength, albeit slightly diminishing air permeability, and accelerated biodegradation in soil, leading to complete degradation within 150 days.
Fuentes et al. [11]	Paper-based bio-composites, alongside other waste-derived materials, like gelatin, corn and wheat waste flour, and sunflower and rice husk, were utilized to develop biodegradable seedling pots.	Tests on water absorption, solubility, tensile strength, and biodegradation were conducted, with gelatin-based bio-composites exhibiting high solubility and water absorption rates. However, paper-based bio-composites showed slower biodegradation rates compared to gelatin-based ones, indicating their potential for prolonged use as compostable containers.
Section B. Research highlighting plant growth indices in paper pulp pots
Lopez and Camberato [12]	Examined various bio-based pots for appearance and durability in greenhouse cultivation.	While wood pulp, sphagnum peat moss, rice straw, and coco fiber pots were susceptible to algae growth and breakage, molded fiber containers (composition: minimum 74% recycled paper; supplier: Western Pulp Products) remained intact and displayed superior plant growth characteristics, including greater shoot and root dry weights and an enhanced bract area index compared to other container types, thus highlighting the advantage of using molded fiber/paper pots for greenhouse crop production.
Seo et al. [13]	Assessed the viability of cylindrical paper pot seedlings for hot pepper cultivation, examining seedling growth and fruit yield under various tray types and fertigation methods.	Results showed comparable growth patterns and fruit yields between paper pot seedlings and conventional plug seedlings, indicating the potential applicability of paper pots for pepper cultivation.
Nambuthiri and Ingram [14]	Conducted plant growth studies to evaluate plantable pots for different types of groundcover plants.	Plants cultivated in paper and bioplastic containers exhibited comparable growth to those in standard plastic containers, and these plantable pots underwent almost complete bio-degradation after four months in the field.
Li et al. [15]	Transplanted Encore azalea ‘Chiffon’ liners into one-gallon containers of black plastic and biodegradable paper, respectively, for growth indices comparison.	Results showed that plants grown in paper containers exhibited increased growth indices, dry weights, leaf area, and root growth compared to those in plastic containers, particularly with nitrogen rates ranging from 10 to 20 mm. Additionally, plants in paper containers had higher nitrogen content despite lower tissue concentrations, suggesting better nutrient uptake efficiency compared to plastic containers.

. Table 1 is divided into 2 sections: Section A summarizes the significant research on paper pulp pots manufacturing and related characteristics, and Section B summarizes the results of various recent research studies highlighting plant growth indices in paper pulp-based nursery pots.

While polyethylene pots remain popular due to their durability and cost-effectiveness [16], biodegradable pots, such as paper pulp pots, are expected to grow in popularity, primarily as sustainability increasingly influences purchasing decisions for gardening pots [17]. As more growers and consumers prioritize environmental considerations, paper pulp pots will likely become a more common choice in horticultural practices. Consequently, we can anticipate a decrease in prices as supply and demand rise, making these eco-friendly alternatives more accessible to all. The rising preference for paper pots is supported by several factors, including growing environmental concerns such as plastic pollution and climate change [3]. Paper pots, being biodegradable and compostable, represent a sustainable alternative to plastic pots, aligning with consumer preferences for environmentally friendly products [3]. As awareness of sustainability practices and demand for sustainable products continue to grow, the adoption of paper pots is expected to increase, reflecting the shift in sustainable trends in home gardening and industrial horticulture [18].

In response to this trend, this paper contributes to sustainable development practices by presenting various quality performance analyses to identify areas for improvement in paper pulp pots and other biodegradable alternatives, ensuring their competitiveness in the evolving market landscape. The evaluation also provides insights into the comparative performance between paper pulp, representing biodegradable pots, and polyethylene pots, which are non-degradable, with regard to plant health, environmental, and economic dimensions. This information carries significant trade-off implications for green sustainability shifts and initiatives in horticultural practices. By examining quality performance metrics, our study offers actionable guidance to industry stakeholders, policymakers, and sustainability practitioners to enhance biodegradable pot material selections and quality management strategies, furthering environmental sustainability goals within the horticultural, industrial, and manufacturing sectors.

2. Materials and Methods

This section outlines the materials procured, and the methods employed in the comparison experiment to assess quality performance in paper pulp and polyethylene pots. The overall procedure of the quality performance comparison study between the two pot materials is summarized in Figure 1. Section 3 and Section 4 will cover the post-greenhouse analysis and potential challenges.

2.1. Materials for Greenhouse Experiment

Three categories of materials employed for the experiment are the plant containers, plant species, and the growing media, as summarized in Figure 1. The greenhouse experiment was conducted primarily to observe the plant growth in 3-inch paper pulp and polyethylene nursery pots. Commercially available paper pulp and polypropylene were used in this experiment. Paper pulp pots are biodegradable and eco-friendly. In contrast, polypropylene pots are non-biodegradable, non-toxic, lightweight, and widely used. The 3 inches is the diameter at the top opening of the pots. Nursery pots refer to the plant containers used for propagating seeds or growing young plants before they are transplanted into larger containers or often directly into the ground. The materials of the pot can affect the growth and development of the root system, as well as its overall health and vigor [19].

It is beneficial to see which plants can thrive and establish themselves well in smaller-diameter pots for several reasons, including space efficiency, specialized plantings, and resource conservation. This knowledge empowers gardeners to create diverse and sustainable garden spaces tailored to their needs and preferences. In this experiment, the performance of pots was compared by planting two similar fruit-bearing plants with Cannonball and Celebrity Tomatoes, leafy plants with Parris Island Lettuce, and flowering plants with French Marigolds. These plant species were selected based on seed availability in the greenhouse at the time of the experiment. Furthermore, we chose these plants because they could be transplanted into larger containers once they outgrew the nursery pots.

The Pro-Mix BX with microbial fungicide by Sun Gro^® Horticulture was used as the growing medium for all plant species and pot materials. Additionally, proper fertilization is crucial for achieving high-quality crops in a greenhouse setting. This study utilized liquid-feeding fertilizer containing 200 parts per million (ppm) of nitrogen (N) and employing Jack’s 20-20-20 fertilizer composition. This all-purpose fertilizer is commercially available with a balanced 1:1:1 NPK ratio, with 20% each of nitrogen (N), phosphorus (P), and potassium (K), which are three essential nutrients required by most plants for healthy growth and development. To prepare this liquid fertilizer, 13.5 ounces of the fertilizer must be dissolved in 100 gallons of water, resulting in a 200 ppm N solution. This concentration is deemed to ensure adequate nutrient supply to the plants, promoting healthy growth and maximizing crop quality.

2.2. Greenhouse Experiment

As shown in Figure 2, the greenhouse experiment has five significant procedures, from seed germination to data collection.

In the seed germination procedure, the seeds were planted in 4-cell packs at North Dakota State University (NDSU) Horticulture Greenhouse. Seeds were grown in these 4-cell packs for four weeks before being transferred to actual pots, as shown in Figure 3a. During the seed germination process, more seeds than needed for the greenhouse experiment were germinated. Observations were made over six weeks until the seeds had germinated and developed into seedlings suitable for transplantation. The assessment primarily relied on visual observations, with only healthy-looking seedlings selected for transplantation.

Four replications were decided for each pot type per plant species to accommodate the possibility of poor seed quality. Hence, eight plants per species were grown and experimented with. Considering we had four plant species, a total number of 32 plants were grown in the greenhouse. After four weeks of seedling growth in plastic trays, the plants were transferred to the 3-inch paper pulp and polyethylene nursery pots. This procedure is called transplantation.

The growth process was designed for a total of six weeks after transplantation. All the plants were fertilized once daily during this period with liquid fertilizer, as described in Section 2.1. Weekly visual analyses were conducted to monitor normal and healthy growth and to observe if there were any signs of diseases. In week 3, a more detailed visual analysis was conducted, and the setup was captured for visual growth comparison, presented in Figure 3b. After three weeks of growth in pots, the following observations were made. The plant growth was significantly stunted or under-developed in paper pulp pots. The plant coloration in 3-inch plastic pots seemed slightly better than in 3-inch paper pulp pots, but the difference was almost negligible at this growth stage. Among all the plant species, the French Marigold exhibited the fastest growth, followed by Parris Island Lettuce. On the other hand, both tomato species appeared to need more time to grow and produce fruit buds fully.

After a 6-week growth period in the 3-inch paper pulp and polyethylene nursery pots, the plants were harvested before final measurements for data collection were taken. This procedure involved removing the plants from the pots, rinsing away the growing media, and separating the fresh mass (stem and leaves) from the root portion. For data collection of pot quality assessment regarding plant growth performance, the measurement variables include plant height (P_H), plant width (P_W), fresh weight (F_W), and root weight (R_W), as shown in Figure 3c. While this whole measurement procedure was carried out, photographs were taken at all the steps for visual analysis, with the different pot types placed side-by-side for better growth comparison and understanding. Figure 4 shows the visual inspection and comparison for all plant species, including all four replications: (a,c,e,g) visual inspection after harvesting before washing away the growing media, and (b,d,f,h) final visual inspections with roots exposed after rinsing away the growing media, respectively. These photographs were taken before separating the fresh mass and the root portion for data collection.

2.3. Quality Performance Analysis

The quality performance analysis of biodegradable paper pulp pots compared to nonbiodegradable polyethylene or plastic pots was conducted post-greenhouse experiments, which included quantitative plant health assessment, decomposition analysis, and techno-economic analysis. The results of these analyses will be elaborated in Section 3.

2.3.1. Plant Health Statistical Analysis

The quantitative plant health assessment involves the previous greenhouse experiment data collection of parameters such as plant height, width, fresh weight, and root weight to evaluate the overall health and growth performance of plants in each type of pot. To quantitatively assess the quality performance of the two pots and to determine if a significant difference in the plant growth quality exists when grown in two different pot materials, an inferential statistic t-test approach was conducted with the following hypothesis.

$$\begin{gathered} \mathrm{N}\mathrm{u}\mathrm{l}\mathrm{l} \mathrm{h}\mathrm{y}\mathrm{p}\mathrm{o}\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{s}\mathrm{i}\mathrm{s} \left(H_0\right):{\mathsf{\mu }}_1={\mathsf{\mu }}_2 \\ \mathrm{A}\mathrm{l}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{n}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{v}\mathrm{e} \mathrm{h}\mathrm{y}\mathrm{p}\mathrm{o}\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{s}\mathrm{i}\mathrm{s} \left(H_1\right):{\mathsf{\mu }}_1\ne {\mathsf{\mu }}_2 \end{gathered}$$

(1)

where ${\mathsf{\mu }}_1$ is the average plant health metric for plants grown in paper pulp pots, and ${\mathsf{\mu }}_2$ is the average plant health metric for plants grown in polyethylene pots. The null hypothesis, H₀, states that there is no difference in the plant health grown in the two kinds of pots [16]. In contrast, the alternative hypothesis, H₁, states there is a difference in plant health between plants grown in paper pulp pots versus those grown in polyethylene pots. A significance level of 5% or 0.05 was employed to verify the hypotheses’ validity. The H₀ will be rejected when the calculated probability value (p-value) is less than a 0.05 significance level. This scenario suggests that the observed difference in the average plant health metrics between the two pot types is statistically significant, agreeing with the H₁. On the other hand, when the obtained p-value is greater than the 0.05 significance level, the H₀ will not be rejected. This scenario suggests that any differences observed in plant health metrics could be attributed to random chance or factors other than the type of pot used in this study.

The t-test uses the t-distribution values and the degrees of freedom to determine statistical significance. The equal variance or pooled t-test was employed for this study because the number of samples collected for each plant health metric for each pot material is the same. More on the t-test can be found in refs. [20,21]. Employing this rigorous statistical approach in analyzing the experimental data aimed to provide valuable insights into the value of biodegradable paper pulp pots compared to traditional plastic pots in supporting plant growth and identifying areas for potential improvement in horticultural practices. The statistical analysis was mainly conducted in Excel (version 2403) with Analysis ToolPak and verified with the statistical software Minitab 21.4.2.

2.3.2. Pot Degradation Analysis

Degradation analysis was conducted to assess the rate at which the paper pulp pots started to break down materials and structures due to various factors such as environmental conditions, chemical reactions, and physical forces. The degradation of the pots can result in a decline in their quality performance, functionality, or integrity. Additionally, analyzing the degradation rate can provide valuable insights into their environmental impact and sustainability at the end of the pots’ lifecycle [22]. Since paper pulp pots are bio-degradable, one of the aims of this experimental study was to determine how much these pots degrade during the six-week utilization period. A short-duration degradation study on nursery pots was conducted using an above-ground experimental set-up approach [16,19,23].

The weights of individual pots were previously measured before the greenhouse experiments, as shown in Figure 5a. After the plant measurement data were recorded at the end of the greenhouse experiments, the paper pulp pots damaged during handling and watering were discarded. Figure 5b shows an example of a damaged paper pulp pot with significantly chipped edges. After a meticulous visual inspection to assess the damaged pots, eight of the sixteen paper pots in the best condition were considered for degradation assessment purposes (Figure 5c). These paper pots were cleaned thoroughly and put in a drying facility. After five days at the drying facility, the weights of the dry paper pots were measured. Monitoring the weight reduction of bioplastics is one of the most standard methods of evaluating their biodegradability [24,25]. After the weight of the dried paper pulp pots was measured, the degradation rate was quantified based on the calculated percentage weight loss, which was carried out by comparing their initial and final weight as follows [19,23,26].

$$Weight Loss (\%)=\frac{W_i-W_f}{W_i}\times 100\mathrm{\%}$$

(2)

where W_i is the weight of the paper pulp pots before the start of the experiments, and W_f is the weight of the paper pulp pots at the end of the experiments. Both weights were measured in grams.

After obtaining the degradation rate, various degradation models were applied to understand the specific degradation patterns involved in the process. This is crucial for improving the quality performance of paper pulp pots that can withstand environmental conditions and maintain their integrity over time. Four degradation models were employed: linear, exponential, logarithmic, and power functions. In the linear degradation model, a constant degradation rate is assumed to occur over time. The exponential degradation model assumes that the degradation rate is exponential to the remaining quantity or the weight of the pot’s material. In contrast, the logarithmic degradation model assumes a decreasing rate of degradation over time, which is also an inverse of the exponential functions. Thus, the degradation patterns of the exponential and logarithmic models are opposite. In the power degradation model, the degradation rate is assumed to be proportional to the power of time. The following equations were employed to quantify these degradation models.

$$\mathrm{L}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{a}\mathrm{r}:D\left(t\right)=D_0-kt$$

(3)

$$\mathrm{E}\mathrm{x}\mathrm{p}\mathrm{o}\mathrm{n}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}:D\left(t\right)=D_0{e}^{\left(-kt\right)}$$

(4)

$$\mathrm{L}\mathrm{o}\mathrm{g}\mathrm{a}\mathrm{r}\mathrm{i}\mathrm{t}\mathrm{h}\mathrm{m}\mathrm{i}\mathrm{c}:D\left(t\right)=D_0/\left(1+kt\right)$$

(5)

$$\mathrm{P}\mathrm{o}\mathrm{w}\mathrm{e}\mathrm{r}:D\left(t\right)=D_0{t}^{-k}$$

(6)

where D(t) is the weight of the pots at time t, D₀ is the initial weight of the pots measured in grams, k is the degradation rate constant obtained from Equation (2), and t is the study time (days, months, years, or cycles). These equations were used to forecast how much the weight and material of the pots change over time as they undergo degradation processes. A two-year study period was employed. To validate the results, degradation data from various published studies on paper pots at 6 months and 1.5 years were compared.

2.3.3. Techno-Economic Analysis

Despite the growing interest in eco-friendly alternatives, paper pulp pots may still face challenges in gaining widespread acceptance in the market. Due to performance and cost concerns, growers and consumers accustomed to plastic pots may hesitate to switch to paper pots [27,28]. Based on previous analyses of plant health and degradation performance, a techno-economic analysis was performed to determine the financial benefits of utilizing biodegradable paper pulp versus polyethylene pots. The technological advantages of implementing paper pots were quantified from a normalized value of the plants’ health performance and degradation rate. The min-max feature scaling was employed to normalize the values of plant health metrics, standardizing the data to ensure the collected data fall within a range of 0 to 1 (X_norm), regardless of their initial units [29].

$$X_{norm}=\frac{X-X_{min}}{X_{max}-X_{min}}$$

(7)

where X is the initial recorded value of plant health metrics P_H, P_W, F_W, or R_W. X_min denotes the minimum value, while X_max represents the maximum value of plant health metrics within the group. The group comprises data from the two different pot materials. To determine the costs, the average market price quotes for paper pulp and polyethylene pots from ten local distributors were obtained. It is important to note that these prices reflect the regional market and may vary based on geographic location, country-specific regulations, or supplier agreements. Additionally, these prices may fluctuate periodically based on the demand-supply, inflation, or currency exchange rates. A generic cost–benefit analysis was conducted to determine the benefit values of technology per dollar.

$${BC}_{ratio}=\frac{\sum Benefits}{\sum Costs}=\frac{B_{PH}+B_D}{C_{MP}}$$

(8)

where BC is the benefit–cost ratio, B_PH is the benefits obtained from the plant health, B_D is the benefits obtained from the degradation, and C_MP is the cost derived from the market price. If the obtained BC_ratio is greater than 1, it indicates that the benefits outweigh the costs, while a BC_ratio less than 1 suggests that costs outweigh the benefits. It should be noted that this short-term techno-economic analysis was conducted from a consumer point of view to evaluate the acceptance of the paper pulp pots. While this straightforward analysis offers valuable insights into the immediate benefits and costs associated with using paper pulp and polyethylene pots, broader impact factors from manufacturing processes, recycling efforts, and other life-cycle aspects may influence the long-term cost–benefit considerations and decision-making processes for stakeholders.

3. Results

3.1. Plant Health Analysis Results

The plant health assessments, in terms of plant growth, were recorded for each plant specimen, and the averages are presented in Figure 6. Plant height and width are measured in centimeters (cm), and the fresh plant and root weights are measured in grams (g). The vertical bars in the column chart represent the average plant growth parameters of various plant species cultivated in both paper pulp and polypropylene nursery pots, and the variations in the data collection are shown as the error bars.

The results presented in Figure 6 show that plants grown in paper pulp pots for Cannonball Tomato and Celebrity Tomato demonstrated plant height and width comparable to those grown in polyethylene pots. However, fresh and root weight observations suggested superior performance for all plant species in polyethylene nursery pots. These results indicate that polyethylene pots may provide more favorable plant growth and development conditions than paper pulp pots. One noteworthy observation is that Parris Island Lettuce grown in paper pulp pots exhibited less variability than in polyethylene pots, as demonstrated by shorter error bars. However, for other plant species, the variability appears to be consistent between the two types of pots. This variability in plant health metrics can be attributed to factors such as growth conditions, soil composition, pot materials, seed quality, and others.

In general, by visual analysis alone, plants grown in paper pulp pots exhibited the least growth across all the plant species. This observation is especially noticeable in the case of Parris Island Lettuce and French Marigold compared to the plants grown in the polyethylene nursery pots. This may be due to the susceptibility of paper pulp pots to high water loss through their porous sidewalls, which subsequently suffer from a high evaporation rate [16]. It is plausible that insufficient water retention in paper pulp pots hindered optimal plant hydration, leading to delayed plant growth [9]. Further investigation and experimental replications are needed to comprehend the specific factors influencing the observed differences in plant health metrics between the two types of pots, including the effect of moisture retention, air exposure, and plant nutrition in the plant growth process.

To quantitatively validate the results from the greenhouse experiment, a statistical approach with t-test hypothesis testing was conducted to discern any significant differences in plant health assessment resulting from using different nursery pots.

Table 2. Quantitative comparison of plant health metrics with t-test hypothesis testing.

Plant Species	t-Test Results *	Plant Height (cm)	Plant Width (cm)	Fresh Weight (g/plant)	Root Weight (g)
Cannonball Tomato	p-value	0.975	0.182	0.006	0.230
	Decision	Accept H0	Accept H0	Reject H0	Accept H0
Celebrity Tomato	p-value	0.910	0.932	0.012	0.036
	Decision	Accept H0	Accept H0	Reject H0	Reject H0
Parris Island Lettuce	p-value	0.017	0.001	0.007	0.039
	Decision	Reject H0	Reject H0	Reject H0	Reject H0
French Marigold	p-value	0.029	0.272	0.115	0.646
	Decision	Reject H0	Accept H0	Accept H0	Accept H0

* Accept H₀ = there is no difference; Reject H₀ = there is a difference in the plant health observed between the two types of pots.

summarizes the t-test hypothesis testing results for each plant health metric and species, presenting the p-values and decisions for the hypothesis in Equation (1).

The results from t-test hypothesis testing provide a quantitative clarification on the differences observed in plant health metrics across various pot types. It reveals no significant difference between plant height and width for the Cannonball and Celebrity Tomatoes grown in different pot materials. However, a significant difference exists in the fresh weight of the tomato plants if they are grown in two different pot materials. While no significant differences were noted in the root weight of Cannonball Tomatoes across paper pulp and polyethylene pots, significant variations in root weight were observed for Celebrity Tomatoes. The same observation in Figure 6 was confirmed by t-test hypothesis testing for Parris Island Lettuce, indicating a significant difference detected across all plant health metrics if grown in different pots. Although t-test hypothesis testing results reveal a substantial difference in French Marigold plant height if grown in different pots, other plant health metrics showed no significant variation. These findings emphasize the substantial impact of pot materials on plant health and highlight potential areas for improvement in paper pulp pots to compete effectively with polyethylene pots across various plant species and cultivation environments.

3.2. Degradation Analysis Results

The initial and final weights of the eight paper pulp pots (in grams) are shown in Figure 7, along with the weight loss percentage of the respective paper pots. The average initial weight was about 8.76 g, and the final weight averaged about 8.68 g. The average degradation rate based on the weight loss of the paper pots during the 6-week use period and after the 5-day drying period was about 0.88% with 1.24% standard. Most of the weight loss data are uniform except in two cases (Pot 1 and Pot 7), which might be attributed to the position of the paper pots during irrigation in the greenhouse. The paper pulp pots positioned at the extremities were less protected and more exposed to environmental elements, such as water or heat, than those placed in the middle among other plant pots. As a result, these pots placed at the extremities might decompose a little more rapidly than the different pots. It also suggests that degradation will occur at a faster rate in an open environment like a landfill, as opposed to a controlled environment such as a greenhouse. Pot 1 exhibited the fastest degradation rate at 2.95%, and Pot 6 showed the slowest degradation rate at 0.08%.

In addition to the degradation rate, analyzing the degradation patterns may offer insights into the long-term quality performance behavior of paper pulp pots. While the degradation rates of the pots can be obtained at the end of the experimental study or plant growth process, obtaining the pots’ degradation patterns experimentally may not be as straightforward as determining their degradation rates. This challenge relates to measuring the pots’ degradation rate over time without damaging the plants and disturbing their growth process. Thus, exploring non-invasive or indirect methods for monitoring degradation patterns while preserving plant health is crucial.

For this effort, the degradation of the pots was assumed to follow a particular degradation pattern. Employing Equations (3)–(6), different degradation patterns were forecasted for up to 2 years. Figure 8 shows the results of a two-year study period for linear (%Lin), exponential (%Exp), logarithmic (%Log), and power (%Pwr) degradation patterns with an average degradation rate k of 0.875%. The fastest degradation behavior follows an exponential pattern, where the paper pots are expected to degrade to 44% of their initial weight in 1.5 years. In contrast, the slowest degradation behavior follows the linear pattern, where the paper pots are expected to retain around 90% of their initial weight in 1.5 years.

To validate the experimental findings and the accuracy of the predicted degradation results, the forecasted degradation process based on various degradation patterns was compared with the degradation data obtained from multiple published studies on paper pulp pots. Two extended timeframes were considered, a 6-month and 1.5-year study period. Figure 8 shows the projected degradation process for the two extended study periods. Additionally, the comparison of degradation projection with published data is summarized in

Table 3. Degradation of paper-based pots in a 6-month study period.

Study Period	Refs.	Pot Materials *	Degradation (%)
	Experiment and data analysis results	Paper pulp (%Lin)	3.04%
		Paper pulp (%Exp)	23.38%
		Paper pulp (%Log)	21.03%
		Paper pulp (%Pwr)	10.96%
	Schrader et al. [26]	Paper (uncoated)	14%
6 months		Paper—single-coated with PU	19%
		Paper—double-coated with PU	12%
	McCabe et al. [30]	Paper fiber	53%
		Paper fiber—PA coat	34%
		Paper fiber—PLA coat	27%
		Paper fiber—PU coat	31%
		Paper fiber—TO coat	27%
	Experiment and data analysis results	Paper Pulp (%Lin)	9.2%
		Paper Pulp (%Exp)	55.5%
		Paper Pulp (%Log)	44.73%
		Paper Pulp (%Pwr)	17.32%
1.5 years	McCabe et al. [30]	Paper fiber	60%
		Paper fiber—PA coat	42%
		Paper fiber—PLA coat	36%
		Paper fiber—PU coat	51%
		Paper fiber—TO coat	34%
	Kratsch et al. [31]	Paper fiber	60%

* PA = polyamide; PLA = poly(lactic acid); PU = polyurethane; and TO = Tung Oil coating.

for the 6-month and the 1.5-year periods.

Based on the comparison results over the 6-month study period, paper pots treated with coatings tend to exhibit either exponential or logarithmic degradation patterns, typically at degradation rates ranging from 20% to 30% of their initial weight. PU single-coated paper pots were observed to degrade by 19% by Schrader et al. [26] and various coatings on paper pots were observed by McCabe et al. [30] to degrade by about 27–34% in 6 months. This deduction is also confirmed for the 1.5-year study period, where most paper pots were observed to degrade about 40–60%, which also seemed to follow exponential or logarithmic patterns. Both McCabe et al. [30] and Kratsch et al. [31] observed that untreated paper fiber pots degraded at a 60% rate over 1.5 years. Coated paper pots degraded more slowly at approximately 35–50% in 1.5 years, according to findings from McCabe et al. [30]. These comparison results emphasize the effectiveness of coatings in preserving the structural integrity of paper pots over extended periods, potentially enhancing their durability in horticultural applications.

While the majority of the references cited in Table 3 were based on studies conducted in soil, their findings remain applicable and can be compared with the presented above-ground experimental setup. The comparison with references aims to demonstrate that the four mathematical models (linear, exponential, logarithmic, and power) can be used to predict the degradation of materials. Building on our previous findings, different materials exhibit distinct degradation patterns, with environmental factors often serving as catalysts in the degradation process. When employing a mathematical model to predict the degradation of a pot over time, it is vital to consider the pot’s material properties.

3.3. Techno-Economic Analysis Results

The techno-economic analysis was conducted based on three components: the benefits from healthier plants or a positive greenhouse experiment outcome, the benefits from the degradation process, and the costs from the consumer point of view in terms of market price.

Table 4. Average market price obtained from 10 local distributors.

Quote	Paper Pulp ($)	Qty	Unit Price ($)/ea	Polyethylene ($)	Qty	Unit Price ($)/ea
1	$8.99	50	$0.18	$9.90	50	$0.20
2	$14.99	100	$0.15	$9.99	100	$0.10
3	$17.99	120	$0.15	$16.99	200	$0.08
4	$14.99	60	$0.25	$23.99	200	$0.12
5	$15.99	100	$0.16	$11.99	100	$0.12
6	$16.99	100	$0.17	$18.99	100	$0.19
7	$17.99	100	$0.18	$8.80	80	$0.11
8	$9.99	50	$0.20	$12.99	100	$0.13
9	$20.99	200	$0.10	$9.99	100	$0.10
10	$13.99	60	$0.23	$7.99	50	$0.16
		Average	$0.18		Average	$0.13

summarizes the results for market price quotes obtained from 10 local distributors in January 2024 for the paper pulp and polyethylene 3-inch round pots.

From the quotes obtained, based on the average unit price, paper pulp pots are $0.05 more expensive per pot than polyethylene pots, which is approximately 40% more in unit price. To assess whether this price differential is justified by the benefits obtained from plant health assessment and degradation, a cost–benefit analysis was conducted with normalized values from plant health assessment and degradation. The results from the cost–benefit study and the components are listed in

Table 5. Cost–benefit analysis results.

Pots	BPH	BD	CMP	BCratio
3-inch paper pulp	0.32	0.875	$0.18	6.74
3-inch polyethylene	0.69	0.000 *	$0.13	5.28

* Polyethylene pots did not degrade during the study period. Thus, the degradation benefits were regarded as zero.

.

The calculated BC_ratio for paper pulp pots was 6.74, higher than the BC_ratio for polyethylene pots at 5.28. This cost–benefit analysis reveals that although paper pulp pots did not outperform polyethylene pots in plant health and are priced higher, their limitations can be compensated for by the environmental advantages derived from the faster degradation process. Therefore, for consumers who prioritize environmental considerations, transitioning to paper pots may not necessarily put them at a significant disadvantage. It should be noted that the results from this analysis do not advocate for a mandatory transition to paper pulp pots. Instead, this analysis aims to help customers understand the trade-offs in selecting a particular pot material. The findings from this study allow customers to make informed decisions based on their priorities and goals by considering various factors.

3.4. Quality Performance Assessment

To summarize the quality performance assessment presented in this paper, the relationship between the results from individual analyses presented in the previous section is combined into a radar chart. This radar chart offers a holistic understanding of the comparative performance of paper pulp and polyethylene pots. A radar chart or spider chart is a graphical representation of multivariate data, providing a two-dimensional visualization that facilitates comparison across various parameters.

Figure 9 shows a radar chart of quality performance assessment representing the relationship between plant health performance, the degradation process, and the market value for paper pulp and polyethylene pots. The three different variables of plant health, degradation, and market value are presented in three equiangular spokes. The data points for each variable are plotted on these spokes and connected to form a triangular shape, with zero value at the center of the triangle. From the radar chart, the quality performance assessment of 3-inch polyethylene pots is depicted by the yellow triangle, while the performance of 3-inch paper pulp pots is indicated by the green triangle.

The plant health and degradation values were derived from the normalized benefit value of the two components from the techno-economic analysis. The market value was employed instead of the market price to ensure consistency across the quality performance components between 0 and 1. The market price value was normalized with Equation (7), with the lowest price holding the best market value and vice versa. From the radar map in Figure 9, the total quality performance value of paper pulp pots was 1.64, and for polyethylene pots, it was 1.41. This short-term analysis, viewed from a consumer perspective, reveals the need for ongoing efforts to enhance the plant health performance of paper pulp pots and potentially reduce the market prices of paper pulp pots.

4. Discussion

4.1. Long-Term Sustainability

Continuous efforts to enhance the quality and performance of paper pulp or other biodegradable pot options may lead to broader application and adoption of sustainable products and ultimately increase consumer acceptance. Having examined the short-term quality performance of paper pulp and traditional polyethylene pots, continuous efforts should be pursued by integrating these findings to foster long-term sustainability. Industrial engineering principles offer valuable frameworks for bridging short-term analysis with long-term sustainability goals, as shown in Figure 10.

Industrial engineering principles emphasize the importance of continuous improvement to enhance processes or products over time [32]. These principles can be implemented iteratively to transform the presented short-term analysis into pathways for long-term sustainability by expanding the scope of the short-term study, deepening the understanding between the cause-and-effect relationship of short-term actions and long-term consequences, and ultimately offering a more comprehensive view of how long-term sustainability can be realized. By analyzing the quality performance of different pot materials, industrial engineering principles can identify areas where processes related to time, cost, and quality can be optimized to improve efficiency [32] in achieving sustainability across environmental, social, and economic dimensions in horticulture and agriculture practice. For example, identifying ways to increase supply by improving the manufacturing process of paper pulp pots to reduce energy consumption or waste generation contributes to sustainability efforts.

4.2. Limitations and Future Work

There are several limitations in the presented short-term quality performance analysis. From the 6-week study period of the greenhouse experiment, this short-term observation might not entirely encompass the long-term implications of plant health and pot durability. Additionally, the current greenhouse experiment was limited to only four plant species: Cannonball Tomatoes, Celebrity Tomatoes, Parris Island Lettuce, and French Marigolds. While these species offer diversity in fruit-bearing, flowering, and leafy plants, they may not fully represent the overall performance of all plant types. Therefore, future research may consider more targeted experiments focusing on specific types of plants to provide a more comprehensive understanding of pot performance.

The degradation analysis reveals the significance of understanding the long-term behavior of paper-based materials in various soil conditions and environmental factors. Adverse growth conditions, excessive humidity, extreme drought, or prolonged exposure to sunlight and UV radiation are known to accelerate degradation processes [33]. However, the presented analysis only included the above-ground experiment where the pots were positioned on benches in the greenhouse. To address this limitation, future greenhouse experiments will include in-soil and above-ground experiment setups, with smaller pots embedded within larger ones for extended observation periods. Additionally, the current study only examined three-inch pot dimensions. Future investigations will also incorporate a variety of pot shapes and dimensions in addition to various pot materials to expand the scope of the greenhouse experiment and degradation analysis.

Moreover, in terms of material properties, to improve plant health performance in paper pulp pots, further investigations will delve into understanding different compositions that can be blended into paper pulp pots to stimulate plant growth and produce healthier plants. One potential drawback of paper pots is that the plants grown in paper pots need more water than those grown in plastic containers [34]. Research focusing on optimizing bio-degradable coating formulations to improve the water retention and durability of paper pulp pots will be explored. While this study did not include elements such as manufacturing processes and life-cycle costs in the techno-economic analysis, they significantly influence the long-term viability of adopting paper pulp pots. Therefore, future research endeavors will include a more detailed techno-economic analysis encompassing an overall life-cycle assessment to provide a more comprehensive understanding of the economic implications and environmental impacts of different pot materials. By incorporating material properties, the manufacturing process, and life-cycle analysis into a more comprehensive economic evaluation, these efforts may contribute to reducing the market prices of paper pulp pots, making them more accessible as a sustainable option for horticultural practices.

Additionally, seed quality significantly influences the overall assessment of plant health. Seed integrity plays a crucial role in determining the performance and robustness of subsequent plant growth. Future replication studies may benefit from incorporating comprehensive germination tests at the beginning of the greenhouse experiment to provide a more comprehensive understanding of seed viability and its implications for overall plant health assessment across various pot materials. In this research, experiments are conducted in a controlled greenhouse environment. The impacts of many factors, such as temperature fluctuations and sunlight, were not considered in this study. Therefore, conducting a degradation study using both above-ground and in-soil experimental setups provides a comprehensive understanding of how materials degrade in different environments. Above-ground setups assess exposure to air, sunlight, and temperature fluctuations, while in-soil setups evaluate biodegradability, soil interaction, and moisture effects.

5. Conclusions

In conclusion, this study delved into the comparative performance of biodegradable paper pulp pots and non-degradable polyethylene nursery pots in horticultural practices. With the rising popularity of environmentally conscious approaches, understanding the implications of pot choice is paramount. With a thorough investigation encompassing plant health, environmental impact, and techno-economic considerations, potential areas of improvement to the paper pulp pots were obtained from this study. The greenhouse experiment, involving four plant species, Cannonball Tomatoes, Celebrity Tomatoes, Parris Island Lettuce, and French Marigold, revealed the quality of plant growth performance within each pot type. Additionally, degradation analysis provided crucial data on the average degradation rate and patterns, further enhancing the understanding of pot sustainability. Techno-economic analysis, including the evaluation of plant health, degradation process, and market price cost–benefit ratios, establishes the viability of market acceptance for paper-based biodegradable nursery pots. By meticulously examining quality performance aspects, this study assists industry decision-makers in enhancing the quality performance of paper pulp pots as a potential effort toward sustainable horticultural practices. This analysis is essential for ensuring competitiveness against traditional non-degradable pots and enhancing customer acceptance of biodegradable pots in the market.