Advancing Sustainability in Pelargonium Nursery Management: Scientific Exploration of an Innovative Prolonged Cold Storage System for Cuttings

Abstract

Cold storage of pelargonium cuttings addresses the issue of nonoverlapping production seasons in Central Europe, where cuttings are harvested from stock plants in December, but rooting begins in mid-February/March. Here, we show an innovative system for cuttings storage using nature-based solutions. We compared post-delivery storage of unrooted cuttings in paperpots maintained in greenhouses (8/6 °C day/night) to standard rooting immediately after delivery. Key factors included genotype (Pelargonium zonale, P. peltatum, and hybrids), four delivery weeks (48–51), two growing seasons (2021 and 2022), and storage duration (up to 4 weeks). Genotype strongly influenced cold storage tolerance, with P. peltatum enduring storage for up to 4 weeks without significant loss of rooting efficiency, unlike P. zonale. The success of storage depended on stock plants’ quality and nutritional status: higher nitrogen content in 2022 cuttings compared to 2021 was associated with reduced rooting in P. zonale and hybrids. Neither delivery timing nor residual ethephon affected rooting outcomes after storage. This study demonstrates that storing pelargonium cuttings for up to two weeks using this method preserves quality while optimizing production efficiency by reducing nursery space, water, fertilizer, and pesticide use. This shift in production practices reduces per-unit costs and enhances the economic viability of bedding young plant producers.

1. Introduction

Vegetative cuttings are an essential means of propagation for many commercially important ornamental species. Pelargonium species are among the most important species in the bedding and balcony annual plant market in European countries and the USA; these plants are propagated vegetatively [1]. Ornamental pelargoniums are divided into four groups—all hybrid species—resulting from intense breeding of native African wild species. The first is Pelargonium ×hortorum zonal pelargonium, named after the original species Pelargonium and has an upright habit and zonation on leaves due to one of its ancestors. The second most common group included ivy pelargonium P. peltatum (syn. P. hederifolium), which has a trailing habit and shiny, ivy-like leaves. The next one is an interspecific hybrid of P. zonale × P. peltatum, and the first commercial cultivars combining the best qualities of these sourced species were introduced to the market in 2005. Finally, P. ×domesticum regal pelargonium is less prevalent on the market due to its demanding care [2,3]. Pelargonium cultivars are available mainly from vegetative cuttings that provide genetic stability and uniform development, allowing production automation [4]. Producers supplying the market with the finished product of potted pelargoniums depend highly on importing high-quality cuttings. Farms in Europe and the USA are purchasing soft cuttings (unrooted or liners) severed from stock plants grown in specialized nurseries located in climates with suitable weather conditions and lower production costs, usually in Central and North Africa, Israel, Turkey, Southern Europe, and Central America [5,6]. The cuttings market is one of the most significant floriculture markets; e.g., in 2018, approximately 4 billion cuttings were produced by the top 10 producers worldwide [5]. In 2021, the total world trade value of ‘Unrooted Cuttings and Slips’ reached 633 million dollars. The top importers of cuttings were the Netherlands ($166 MM), the United States ($116 MM), Germany ($72 MM), Canada ($39.2 MM), and Italy ($34.6 MM) [7].

Production stock plants for pelargoniums are planted in the greenhouse from the end of July through August, so the cuttings will be ready for the peak cutting season of mid-November through early February. Pelargonium cuttings are harvested at a rate of 2–3 cuttings per stock plant per week or a total of 30–45 cuttings/m²/week. Foliar applications of ethephon are made weekly during the early weeks of stock plant production, and this is the preferred method for aborting flowers [8]. Ethephon also promotes the branching of some species. However, ethephon applications need to be terminated before the cutting harvest season begins since ethephon causes ethylene to continue to be produced in plant tissue for several weeks after its application [9]. Late applications of ethephon result in increased ethylene production in the postharvest environment, causing leaf yellowing and leaf abscission during the first days of rooting. After being detached from the mother plant, a cutting is typically composed of a small shoot that is 2–5 cm long and possesses a shoot tip and 2–5 leaves. After harvesting in the greenhouse, the cuttings were bagged, marked, coded, inspected for pests and diseases, and packed in boxes to be stored in controlled environments (temp +5 °C to max +10 °C). Then, the unrooted cuttings are distributed to customers, mainly by air, which takes another day or two, for 48–72 h from harvesting to delivery at the customer’s greenhouse [6].

Greenhouse growers rely significantly on the production of stock plants, as these plants directly impact rooting performance. This success is intertwined with the harvested cuttings’ quality, the postharvest environmental conditions, and the time spent in storage and shipping. Extended exposure to a postharvest environment consistently diminishes the performance of cuttings [6]. Once unrooted cuttings are received by the grower, they are inserted into the substrate and misted for a few days until they regain turgor. Then, in the following few weeks (3–5), depending on the cultivar), plants develop adventitious roots through the callus phase. Environmental and cultural conditions are adjusted for each propagation stage [10].

Nurseries specializing in pelargoniums in Europe face challenges with rooting issues attributed to the subpar quality of cuttings provided in winter combined with problems from the prolonged shipping period affecting the viability and rooting ability of the cuttings [11]. The usual production timeline for rooted cuttings of an appropriate size for the stock market is up to 5 weeks [12]. The discrepancy between the maximum productivity of the stock plants (December) and the maximum demand in the market, which occurs in February in the case of pelargonium cuttings, results in a considerable loss of cuttings, which is unacceptable for logistical reasons. This forces the planting of an excessive quantity of cuttings, which increases costs and escalates environmental pressure (greater volume of transported cargo, larger growing area in heated greenhouses, and greater water and fertilizer consumption). Thus, delaying and staggering the production cycle is necessary to eliminate losses due to the overgrowth of rooted cuttings. To this end, their storage has long been advocated, often using ethylene inhibitors [13,14]. However, such methods could be more effective and require chemical treatment, which is undesirable when considering maximum sustainability in horticultural production [15]. In this respect, additional environmental problems may be encountered while cultivating nursery stock in Africa.

In our research, which was conducted under operational conditions using thousands of cuttings of dozens of pelargonium varieties over two growing seasons, we attempted to answer the questions of whether and to what extent it is possible to store unrooted cuttings without the use of chemicals or using natural winter conditions to slow the growth of cuttings. We also investigated the extent to which the initial conditions of the cuttings affected the rooting process. We also studied the effect of ethephon content and the degree of mineral nutrition on rooting efficiency under cold storage conditions. The research aimed to assess the impact of the proposed technology on both the productivity and economic efficiency of the production process. It sought to demonstrate that the changes in the production system would enhance the company’s financial performance while reducing water usage, fertilizers, and chemical plant protection products used in the pelargonium nursery. These improvements, in turn, contribute to lowering CO₂ emissions and the overall carbon footprint associated with pelargonium production.

2. Materials and Methods

2.1. Plant Material and Experimental Design

Experiments were conducted during the 2020/21 and 2021/22 growing seasons on pelargonium cultivars from 3 different groups: Pelargonium zonale, P. peltatum, and P. zonale × peltatum. A total of 15 and 21 varieties were used in the experiments in 2020/21 and 2021/22, respectively (

Table 1. Pelargonium cultivars were tested in the experiment during two cultivation seasons, 2021 and 2022.

Cultivar	Species (Variety Group)	Flower Color	Breeder/ License	Observation Year
Champion Fire Red	P. peltatum × zonale 1	red	Psenner	2021, 2022
Champion Flamingo	P. peltatum × zonale	pink	Psenner	2022
Champion Magic	P. peltatum × zonale	pink	Psenner	2022
Champion Neon	P. peltatum × zonale	purple pink	Psenner	2021
Champion Red	P. peltatum × zonale	red	Psenner	2021, 2022
Champion Salmon	P. peltatum × zonale	salmon	Psenner	2022
Anthony	P. zonale	red	PAC	2021, 2022
Flower Fairy Berry	P. zonale	deep pink	PAC	2021, 2022
Flower Fairy Red	P. zonale	deep pink	PAC	2021, 2022
Flower Fairy Velvet	P. zonale	purple	PAC	2021, 2022
Flower Fairy Violet	P. zonale	violet	PAC	2022
Flower Fairy White	P. zonale	light pink	PAC	2021, 2022
Francesco	P. zonale	deep purple	Psenner	2021, 2022
Leonardo	P. zonale	red	Psenner	2021, 2022
Victor	P. zonale	red	PAC	2021, 2022
Allegria Early Red	P. peltatum	red	Psenner	2022
Allegria Fuoco	P. peltatum	red	Psenner	2021, 2022
Allegria Mex	P. peltatum	red‒pink	Psenner	2022
Allegria Single Neon	P. peltatum	deep pink	Psenner	2022
Allegria Velvet Red	P. peltatum	red	Psenner	2022
Decora Red	P. peltatum	red	-	2022
Rocky	P. peltatum	pink	PAC	2021
Ruby	P. peltatum	red	PAC	2021
VDP (Ville de Paris) Rot	P. peltatum	red	-	2021, 2022

¹ Pelargonium interspecific hybrid.

). The discrepancy in the number of varieties can be attributed to the execution of the experiment under the company’s operational conditions. The selection of varieties was contingent upon commercial importance, market demand and trends. Consequently, certain varieties examined in 2021 were not incorporated into the 2022 study. Conversely, the decision was taken to augment the number of varieties in 2022.

Research on the effect of long-term cold storage (0, 1, 2, 3 or 4 weeks) of unrooted cuttings on plant quality was conducted on the Plantpol production farm (Poland) (coordinate: 50°1′30.4″N 19°14′48.47″E) in Poland. Figure 1 shows the plan of the experiment. Cuttings were obtained from a professional nursery in Kenya, the Company Savanna Flowers (coordinate: 0°42′15.559″S 36°25′37.358″E). Terminal stem cuttings with three to four leaves (one fully developed) were severed from stock plants in Kenya at one-week intervals (weeks 48, 49, 50, and 51) in 2020 and 2021. Unrooted cuttings were packed in perforated polyethene bags (100 in each), immediately cooled to a temperature less than 8 °C, parceled in carton boxes, and then transported by truck to the airport in Nairobi to be delivered to Amsterdam airport (the Netherlands) during the night on a direct cargo flight. The cuttings were delivered from the Amsterdam airport by truck and reached their destination: Production Farm Plantpol in Zaborze (Poland). The entire logistic process from the nursery in Kenya to the production company in Poland took up to 4 days (60–72 h) at low, controlled, and monitored temperatures (2.5 °C to 15 °C, mean 8 °C) in the dark. This is the standard procedure for commercial deliveries of unrooted bedding and balcony ornamental plants.

2.2. Storage Conditions for Unrooted Cuttings

On the days of delivery (the 6th, 13th, 20th, and 30th of December 2020; weeks: 49, 50, 51, and 52; and the same was repeated in 2021 and 2022), cuttings were inserted in paperpot plugs filled with the commercial substrate labeled with the supplier’s code (SoMi 537), consisting of 30% coconut fiber, 40% fine sod peat, 15% polystyrene, 15% perlite, wetting agent (Hawita, Vechta, Germany), pH 5.3, and placed in 104 plastic plug trays (HerkuPlant, Ering, Germany) at a density of 52 plugs (paperpots) per tray for stabilization. After delivery and before planting, the dry matter, ethephon, macro- and micronutrient levels, and heavy metal concentrations of the unrooted cuttings were assessed. Trays with cuttings in paperpots were placed on cultivation benches in an innovative greenhouse equipped with extensive environmental control technology. The environmental conditions during storage were maintained by the climate computer SERCOM SC800 and SercoVision 6 software (Regeltechniek BV, Lisse, the Netherlands) and were the same for each tested batch of pelargonium. The heating/ventilation set points for temperatures of 8 °C (day) and 6 °C (night) provided an average air temperature of 7 °C and an average relative humidity (RH) of 80–90%, automatically maintained by the high-pressure fogging system. Watering was initially performed by sprinklers every 2 h (during the day, on the day of sticking unrooted cuttings and after 24 h), and the spray pulse length was 7 s, followed by ebb and flow irrigation on the benches. The light intensity setpoint for shading was 30 klx, meaning that the automatic shading system was activated when the light intensity reached 30 klx (about 500 µmol/m²/s of PPFD—Photosynthetic Photon Flux Density). The plant fertilization scheme during storage consisted of providing the NPK fertilizer Granusol WSF 17-10-17 (Mivena, Waalwijk, Netherlands) at a concentration of 0.5 (mS/cm EC) in the form of foliar fertilization. This treatment was performed initially for several days until the cuttings regained turgor. Then, the plants were fed daily via foliage, and after the roots started to appear, the plants were fertigated every two days (EC of nutrient solution was 1.0–1.5 mS/cm). Additionally, a preventive protection program against fungal disease was implemented by spraying with the fungicide Signum 33 WG (BASF) at a concentration of 0.1% once a week. The storage conditions in the experimental greenhouse were the same for each tested batch of plants in each cultivation season. The plan of the experiment is presented in Figure 1.

2.3. Rooting Conditions of the Cuttings

After the storage stage (5 batches of different cold storage lengths: 0, 1, 2, 3, and 4 weeks; from each delivery at weeks 48, 49, 50, and 51), the trays of cuttings were transferred to the greenhouse under optimal rooting conditions. The temperature was raised to 22/20 °C day/night. The light intensity and relative humidity parameters were the same as those used during the storage stage. Fertilization and antifungal treatment were continued. During the rooting process, a standard dwarfing procedure was applied by spraying CCC (Stabilan 750SL, Nufarm, Düsseldorf, Germany) at a concentration of 0.1% once a week.

The final rooting response was evaluated after 4 weeks of rooting by assessing the percentage of well-developed liners with visible root systems beneath the paperpot cover. The size of each plug in the batch was evaluated. The findings are expressed as the percentage of rotten cuttings calculated as the proportion (%) of the number of low-quality young plants (those with symptoms of decay, leaf senescence, and yellowing, not well-developed adventitious roots) relative to the initial number of cuttings placed in the rooting stage. SPAD values were measured during the storage stage on the 2nd, 7th, 14th, 21st, and 28th days after the unrooted cuttings were planted into paperpots to obtain additional information about the response to cold storage. In each treatment (delivery date and length of storage), the cuttings were divided into four replicate lots, each consisting of 6 plug trays (312 cuttings) and a minimum of 2 plug trays (104 cuttings) of each variety.

2.4. Ethephon Determination in Unrooted Pelargonium Cuttings Using the LC–MS/MS Technique

Representative varieties from each of the three groups of pelargonium plants were selected to test the ethephon residue level; in 2021, 5 varieties were used, and in 2022, ‘Flower Fairy Violet’ was added to this set. For the quantitative determination of ethephon in the pelargonium cutting samples, dispersion tests were performed via the SPE-QuEChERS modular method and the LC‒MS/MS analysis method according to the norm PN-EN 15662 [16]. Prior to the analysis, the cuttings samples were frozen and stored at −20 °C. Immediately before the analysis, frozen samples of pelargonium cuttings were cut into pieces approximately 0.5 cm in length with a knife. Then, 10 g of the defrosted sample was collected into a 50 mL falcon tube, after which 10 mL of redistilled water, 10 mL of acetonitrile, and 100 µL of the internal standard (TDCPP; Tris(1,3-dichloro-2-propyl)phosphate) were added at a concentration of 10 µg/mL, and 50 µL of 5% formic acid was added. The falcon tube was capped and shaken on a reciprocating shaker for 1 min at 300 movements/min. Then, a mixture containing 4 g of MgSO₄, 1 g of NaCl, 0.5 g of sodium hydrogen citric acid hexahydrate, and 1 g of sodium citric acid dihydrate were added to the test tube. Immediately after adding the mixture of these chemicals, the tube was immediately capped and shaken again for 1 min on a reciprocating shaker at 300 movements/min. The samples were centrifuged for 5 min at 3000 rpm at a temperature of 5 °C. Subsequently, 6 mL of supernatant was collected into a 15 mL falcon tube containing a mixture of chemical reagents: 150 mg of PSA, 900 mg of magnesium sulphate (VI), and 45 mg of GCB. The samples were again shaken for 1 min at 300 movements/min and then centrifuged for 5 min at 3000 rpm at a temperature reduced to 5 °C. Then, 1.5 mL of the supernatant was transferred to a 1.5 mL Eppendorf tube and centrifuged at 10,000 rpm for 5 min. In the next step, 1 mL of the supernatant was transferred to chromatographic vials, screwed on with a septum, and analyzed using the LC‒MS/MS technique.

The analysis of the ethephon content was performed by LC–MS/MS using an HPLC Sciex Exion LC (SCIEX, Framingham, MA, USA) and a mass spectrometer detector (Scan 4500QTRAP), (SCIEX, Framingham, MA, USA). A Phenomenex Aqua chromatographic column (3 µm C18 125 Å, 50 × 2 mm) and a precolumn (C18 4 × 2.0 mm Phenomenex) were used for ethephon analysis. The temperature of the thermostat was 40 °C. A 5 mM solution of ammonium acetate in demineralized water (phase A) and a 5 mM solution of ammonium acetate in methanol (phase B) were used as the mobile phases. The eluent flow rate was 0.3 mL/min, the sample injection volume was 5 µL, and the analysis time was 14.8 min. The parameters of the electrospray ionization source operating in the negative ionization mode in the Scheduled MRM (Multiple Reaction Monitoring) mode are presented in MRM pairs monitored for ethephon: 143.01/78.8 and 143.01/107.0. The analysis was performed using the Analyst 1.7.x software, and the results were processed using the MultiQuant 3.0.3 software.

2.5. Determination of Dry Matter, Macro- and Microelements, Beneficial Elements, and Heavy Metals in Unrooted Pelargonium Cuttings

On the day of delivery, the nutritional status of the cuttings was estimated by testing the dry matter content, the levels of macro- and microelements, and the heavy metal content by sampling whole cuttings (shoot and leaves). The same selected pelargonium cultivars were tested for ethephon determination. The dry matter content was measured by the drying method at 105 °C. The contents of macro- and micronutrients, beneficial elements, and trace elements were also observed. To analyze these elements, the samples were dried at 70 °C and ground on a laboratory mill using a sieve with a mesh size of 0.2 mm (FRITSCH Pulverisette 14; FRITSCH GmbH, Weimar, Germany). Sequentially dried and ground samples were stored in sealed polyethene bags at room temperature (app. 20–22 °C). The Kjeldahl method determined the nitrogen (N) content using oven mineralization, a Foss Digestor 2020 by TecatorTM and a Velp UDK 139 semiautomatic distillation unit [17]. To analyze the contents of the other elements mentioned earlier, microwave mineralization of the plant material samples was performed according to the following procedure: 0.5 g samples were placed into 55 mL TFM vessels, 10 mL of 65% super pure HNO₃ (Merck no. 100443.2500, Darmstadt, Germany) was added, and the samples were finally mineralized in a Mars 5 Xpress (CEM, Matthews, NC, USA) microwave digestion system [17]. After the mineralization, P, K, Mg, S, Ca, and Na contents were determined using high-dispersion inductively coupled plasma optical emission (ICP‒OES; Prodigy Teledyne Leeman Labs, Mason, OH, USA) [18]. The contents of Li, B, Al, Ti, V, Cr, Mn, Cu, Zn, Sr, Mo, Cd, and Pb were measured using triple quadruple spectrometer ICP‒MS/MS (inductively coupled plasma‒mass spectrometry) with an iCAP TQ ICP‒MS (Thermo Fisher Scientific, Bremen, Germany) [18].

2.6. Chlorophyll Measurements

Chlorophyll meter readings (SPAD values) were repeatedly taken at the center of the leaves throughout the cold storage stage experiments. The measurements were taken in the greenhouse between 11:00 and 13:00 with the use of a SPAD-502 plus (Minolta, Osaka, Japan). During the SPAD measurements, the environmental parameters were as follows: light intensity ranged from 10 to 16 klx (200–300 µmol/m²/s), temperature was between 20 and 21 °C, and relative humidity varied between 60 and 70%. The adaxial side of the leaves was always placed toward the emitting window of the instrument, and major veins were avoided. One mature leaf was removed from an unrooted pelargonium, measured on the second day after arrival, stuck in the paperpots, and later after the cold storage period’s 7th, 14th, 21st, and 28th days (depending upon the treatment). One hundred leaves of each cultivar were sampled on each observation date.

2.7. Statistical Analyses

Statistical analyses were performed with Statistica 13.1 software (Dell, Round Rock, TX, USA). Multivariate variance analysis in the GLM (general linear model) module was used to determine the statistical significance of the effects of the factors used in the experiment (varieties/species, length of cold storage, year and cutting time). Linear correlation coefficients were calculated in the multiple regression module.

2.8. Economic Analyses

The economic analyses were conducted using differential (partial budgeting) calculations to compare the relative profitability of two production technologies: standard technology (used previously) and modified technology (involving the storage of unrooted cuttings). Differential calculations assess the relative profitability of alternative solutions by comparing the specific costs that differentiate the technologies. These calculations refer directly to the fundamental economic category of alternative costs or, in other words, the costs of lost benefits [19]. A key feature of differential calculations is the exclusion of standard costs shared by both technologies. The differences between the two technologies were identified when implementing this approach, assuming both aim to produce the same volume of market-ready products. The analysis, therefore, focused on how each technology impacted unit production costs. The study was carried out in four stages, with the first step identifying cost-driving differences between the technologies. The stages were as follows: I. Production of unrooted cuttings in Kenya (stock plants nursery in Kenya); II. Transport of cuttings to the company in Poland; III. Storage of unrooted cuttings in Poland; IV. Production of rooted cuttings, with an emphasis on labor costs. In the second step, the required area of the pelargonium stock plant nursery to achieve the target production volume of cuttings was estimated. This was based on experiment data, including stock plant productivity and loss rates during cuttings production. The third step involved gathering information directly from the young plant producer (Plantpol) regarding the production organization and associated costs at each stage. Currency exchange rates complemented these data as costs arose in different monetary zones.

Certain assumptions and simplifications were necessary for the calculations: 1. The number of cuttings produced per m² of the stock plants: 37 units; 2. Loss rates: 5% for standard technology and 15% during the first four weeks for the modified technology, followed by 5% thereafter; 3. Transport costs for unrooted cuttings were assumed to be the same in both technologies, with differences arising from the number of cuttings transported; 4. Storing unrooted cuttings in Poland for the first four weeks required additional costs for chemical crop protection, fertilization, and greenhouse heating; 5. In the standard technology, additional workers were hired through employment agencies for sprouting, whereas in the modified technology, existing company labor resources—usually underutilized during the winter—were used for the first four weeks.

These steps ensured a thorough evaluation of the cost implications of each technology, focusing on the impact on unit production costs while maintaining comparable production outputs.

3. Results

The rooting efficiency of pelargonium plants was significantly affected by all the factors studied in our experiment: the year of the experiment (production season), cultivar, cutting time, and length of cold storage. In the 2020/21 production season, the mean rooting efficiency was 91.01%, while in 2021/22, it was 84.6%. However, slightly different sets of cultivars were used in both years, and a detailed analysis of the differences between years was performed on the narrowed set of cultivars commonly and in more detail analyzed in both production seasons. As shown in Figure 1, the tested cultivars differed in their response to cold storage. The result of high tolerance to cold storage is noticeable for P. peltatum, especially for ‘VDP rot’, in the 2021/22 season, when most varieties had problems rooting after cold storage. Generally, cuttings of P. peltatum stored for 4 weeks were rooted in 84–96% of the plants, showing satisfactory results. Cultivars from the ‘Champion’ group (interspecific hybrids) can also be considered tolerant to cold storage (Figure 2). However, for most cultivars of P. zonale, a storage period longer than 2 weeks resulted in a strong decline in rooting. This was especially noticeable in the second growing season (Figure 2 and Figure 3A).

The length of cold storage did not affect the chlorophyll content of the leafy cuttings, as indicated by the SPAD index (Figure 3B and Figure 4). In all the treatments, the chlorophyll contents were not significantly different. They did not interplay with the rooting efficiency of specific cultivars. An analysis of the differences among the years revealed that the chlorophyll content in the second season (year 2022) was generally lower than that in the previous year (Figure 4).

Differences in the chlorophyll content in the tested pelargonium plants were noticeable but genotype dependent. The cultivars’ chlorophyll contents were not affected by the production season or the length of cold storage (Figure 4, Supplementary Figure S1 and Table S1).

These results were highlighted by correlation analyses between cold storage, rooting efficiency, and chlorophyll level. As presented in

Table 2. Correlation coefficients (Pearson’s) between rooting efficiency and chlorophyll content for all pelargonium varieties studied in the experiment. The coefficients underlined are statistically significant at p = 0.05.

Year	Cool Storage Length (Days)
	7	14	21	28	All
2021	−0.156	−0.057	−0.083	−0.267	−0.136
2022	−0.052	0.088	0.431	0.216	0.111

, reduced chlorophyll levels were positively correlated with rooting efficiency, especially after 3 and 4 weeks of storage, but only in 2022. In this season, most cultivars had problems rooting after cold storage. The opposite correlation was detected in 2021 (Table 2).

We investigated whether the stock plant production conditions and nutritional status of the harvested cuttings affect the success of cold storage and the subsequent success of rooting and pelargonium liner production. To elucidate the relationships involved, we tested sample pelargonium varieties (2021, 5 varieties; 2022, 6 varieties), which represent different groups, to determine the initial water content, ethephon residues, concentrations of macro- and microelements, and heavy metals immediately after delivery to the farm. Considering all the cultivars, the results indicated significant differences between the 2021 and 2022 production seasons (

Table 3. Rooting efficiency (%), water (%), ethephon, and mineral element contents of unrooted cuttings of five pelargonium varieties were studied in detail in both years of the experiment (mg/kg dry weight); (ns)—the difference between years is statistically insignificant for p = 0.05 (F test).

Year	Rooting (%)	Ethephon	H2O (%)	N	Na	Mg	P (ns)	S	K	Ca	Li	B
2021	92.36	0.0016	87.066	31,583	1056.6	5239.8	6412.2	3184.3	61,391.8	27,976	0.7021	27.003
2022	70.09	0.0006	86.138	34,524	831.20	3271.6	6644.7	3545.4	35,419.7	18,906	0.4077	39.979
Year	Al	Ti	V (ns)	Cr	Mn	Fe	Cu	Zn	Sr	Mo (ns)	Cd	Pb
2021	26.716	20.561	0.0443	1.6298	97.761	78.747	21.593	49.807	193.54	11.466	0.0341	0.0982
2022	56.595	14.086	0.0350	0.9119	147.64	109.13	18.767	72.570	103.25	9.4126	0.0110	0.0315

).

Subsequent batches delivered in weeks 48, 49, 50, or 51 or between the observed features did not show substantial differences (Supplementary Table S1 and Figure S2).

By analyzing the mean content of quantified constituents across all deliveries, it can be asserted that the cuttings from 2022 were less hydrated than those from 2021 and held fewer ethephon residues. Focusing on the mineral elements, the cuttings contained more N, S, B, Al, Mn, Fe, and Zn but also contained less Mg and Ca and less Na, K, Li, Ti, Cr, Cu, Sr, Cd, and Pb in 2022 than in 2021 (Table 3); however, in the second season, the chlorophyll content in the cuttings decreased, as mentioned before (Figure 3). Moreover, the observed phosphorus levels in 2022 exhibited an increase, although this difference was not statistically significant. This can be explained by possible differences in production and stock plant nursery management, especially fertilization and watering.

Correlation analyses revealed the influences of the chlorophyll level, rooting efficiency, and cutting nutritional status, and they confirmed differences between cultivation seasons (

Table 4. Correlation coefficients (Pearson’s) between rooting efficiency and chlorophyll (Chl.), water and ethephon (Eth.) contents, and the contents of mineral elements in unrooted cuttings of five pelargonium varieties were studied in detail during both years of the experiment. The coefficients underlined are statistically significant at p = 0.05.

Trait	Both Years				2021				2022
	Rooting	Chl.	Eth.	H2O	Rooting	Chl.	Eth.	H2O	Rooting	Chl.	Eth.	H2O
Rooting	1.000	0.357	0.234	0.095	1.000	0.267	0.045	−0.175	1.000	0.387	−0.304	−0.047
Chl.	0.357	1.000	0.187	0.022	0.267	1.000	0.175	−0.093	0.387	1.000	0.120	0.042
Eth.	0.234	0.187	1.000	−0.115	0.045	0.175	1.000	−0.404	−0.304	0.120	1.000	0.010
H2O	0.095	0.022	−0.115	1.000	−0.175	−0.093	−0.404	1.000	−0.047	0.042	0.010	1.000
N	−0.528	−0.121	−0.436	0.050	0.026	−0.259	−0.431	0.131	−0.337	0.120	0.237	0.364
Na	−0.154	−0.400	0.081	0.370	−0.587	−0.161	−0.225	0.234	−0.584	−0.769	0.181	0.377
Mg	0.460	0.302	0.665	0.358	0.410	0.350	0.651	0.092	−0.457	0.344	0.404	0.616
P	−0.525	−0.141	0.094	0.063	−0.318	−0.318	0.148	−0.388	−0.697	0.025	0.443	0.522
S	−0.672	−0.237	−0.191	−0.079	−0.225	−0.398	0.013	−0.242	−0.637	−0.042	0.351	0.299
K	0.440	0.100	0.583	0.404	−0.198	−0.136	0.439	0.470	−0.485	−0.022	0.444	0.414
Ca	0.294	−0.040	0.582	0.214	0.296	−0.062	0.452	0.073	−0.689	−0.486	0.181	0.058
Li	0.415	0.173	0.590	0.426	0.132	−0.023	0.506	0.244	−0.263	0.247	−0.024	0.641
B	−0.632	0.009	−0.259	−0.160	0.164	0.288	0.687	−0.286	−0.335	0.293	0.112	0.275
Al.	−0.055	0.019	0.060	0.059	0.089	−0.049	0.668	−0.616	0.341	0.166	0.111	0.605
Ti	0.132	−0.110	0.663	0.068	0.170	−0.096	0.656	−0.408	−0.764	−0.478	0.133	0.319
V	0.107	0.029	0.575	−0.166	0.138	0.035	0.626	−0.540	−0.059	−0.054	0.132	0.505
Cr	0.238	0.027	0.304	0.267	−0.332	−0.233	0.004	0.237	−0.141	0.238	0.678	0.056
Mn	−0.600	0.108	−0.060	−0.115	0.331	0.629	0.593	−0.028	−0.487	0.096	0.222	0.115
Fe	−0.668	−0.109	0.093	−0.209	0.131	−0.122	0.687	−0.555	−0.693	0.051	0.446	0.297
Cu	0.076	0.331	0.343	0.494	−0.259	0.316	0.101	0.151	−0.325	0.284	0.484	0.658
Zn	−0.536	0.251	−0.115	−0.112	0.191	0.570	0.633	−0.250	−0.243	0.525	0.281	0.271
Sr	0.439	0.066	0.655	0.105	0.255	−0.121	0.616	−0.094	−0.430	−0.111	0.231	−0.327
Mo	0.298	0.397	−0.181	−0.106	−0.042	0.270	−0.509	−0.005	0.241	0.453	−0.177	−0.354
Cd	0.288	0.118	0.656	0.087	0.117	−0.043	0.542	−0.082	−0.516	0.240	0.454	−0.100

). A negative correlation was observed between the nitrogen (N) content and rooting efficiency. This observation signifies that greater rooting efficiency is associated with lower nitrogen content, a trend consistent across both years of the study. Notably, significant negative correlations were also detected for the contents of phosphorus (P), sulfur (S), and iron (Fe), indicating that higher levels of these elements do not support rooting. Notably, aluminum, molybdenum, and zinc concentrations exhibited no positive correlations with rooting efficiency. When considering potassium (K) levels, a positive correlation emerged when the data from both seasons were aggregated. However, when analyzed separately for each year, a negative correlation was found, and this negative relationship proved to be statistically significant in 2022. Notably, the K content was reduced by half in 2022, during which rooting efficiency had already diminished. The seemingly positive overall correlation in K content can be attributed to substantial year-to-year variations in K levels.

No significant correlations were detected between ethephon residue, rooting efficiency, or chlorophyll content (Table 4). In both years, trace ethephon concentrations did not affect the rooting response. Nevertheless, a positive correlation was identified between ethephon, trace elements, and potassium (K), as detailed in Table 4.

Focusing on the effect of the delivery week and rooting response, there was no significant difference regarding delivery; however, there was a considerable reduction in rooting in 2022 compared with 2021 (Figure 5A–D).

Additionally, the cultivars in each batch were rooted equally in 2021, opposite to 2022, where the results varied greatly, and no clear conclusions or trends could be drawn (Supplementary Figure S2). In 2022, the cuttings were less hydrated in the last three weeks after delivery, but this did not affect rooting during subsequent delivery. Hydration may be a genotype-dependent feature because there were visible differences in hydration between cultivars; for example, ‘Victor’ had high hydration, and ‘VPD’ had low hydration; nevertheless, ‘VDP’ is a variety that is highly tolerant to storage and roots even after 4 weeks of cold storage (Figure 5C, Supplementary Figure S2). The initial ethephon residues were more significant in 2021 than in 2022, and the differences between the varieties and delivery weeks were minor, ranging from 0.0043 to 0.0002 mg/kg dw (Figure 5D, Supplementary Figure S2).

Examining the mineral compositions in conjunction with the delivery dates, it can be deduced that, in the year 2022, there was a notable increase in the total nitrogen (N) content, independent of the delivery date (harvest). The distinctions observed between subsequent years concerning delivery dates are insignificant and erratic. However, the conspicuous increase in N content in 2022 implies a divergence in the management practices within the nursery. Concomitantly, the levels of magnesium (Mg), sodium (Na), and potassium (K) in 2022 are expected to decrease. As previously indicated, these elements exhibit negative correlations with rooting efficiency (Figure 6A–D). Moreover, the results of the varietal analysis did not significantly differ (Supplementary Figure S2). Notably, the varieties under study exhibited marked disparities in their macro- and microelement profiles. This variability is particularly evident in the case of varieties such as ‘VDP’, characterized by relatively lower levels of Na, K, and Mg, especially in 2022. Conversely, varieties such as ‘Victor’ and ‘Champion’ exhibited higher concentrations of these elements. In light of these findings, it is conceivable that robust varietal trends manifested in 2022 because the stock plants were cultivated under conditions of mineral deficiency, consequently leading to heightened utilization of available nutrients (Figure 6A–D).

The proposed modification to the production technology reduces the pelargonium stock plants growing area by 26.4%, leading to a 25% decrease in water, fertilizer, and use of agrochemicals (

Table 5. Calculate special costs differentiating the current and modified production technology, including storing unrooted cuttings and exploiting earlier stock plant cultivation in Kenya.

Special Costs	Change in Costs in Modified Production Technology
	Increase (+) Decrease (−)	Calculated per 1000 pcs. of Rooted Cuttings (Euro)
Lease and maintenance of the pelargonium stock plants in Kenya (mainly change in the plant cultivation area)	(−)	23.5
Import of unrooted cuttings (including transport, airport and border fees)	(+)	0.5
Labor in Poland (including reduction in seasonal workers)	(−)	2.6
Storage of unrooted cuttings (including additional fertilization, chemical protection, and greenhouse heating)	(+)	0.6
Total	(−)	25.0

).

This lowers CO₂ emissions and the carbon footprint of pelargonium production and generates economic savings. By reducing the mother bed area and extending its usage time, the cost of producing 1000 cuttings is reduced by €23.55. In Poland, these changes lower labor costs by €2.57 per 1000 cuttings. However, due to higher losses when storing unrooted cuttings, an additional 3.1% of plant material must be imported. This slightly increases chemical protection, fertilization, and care costs, estimated at €1.13 per 1000 cuttings. Overall, the technology change saves nearly €25 per 1000 cuttings delivered to the market, reducing production costs by 5–7%, depending on the variety (Table 5). These improvements positively impacts the company’s overall economic performance.

4. Discussion

Numerous researchers have explored the feasibility of employing storage techniques for pelargonium cuttings and various other bedding plant species to increase quality and mitigate losses in the context of transportation [20,21,22,23]. Short-term storage of unrooted cuttings is currently a standard procedure associated with the necessary transportation of plant material. Transport occurs within 2–4 days at a controlled temperature of 5–12 °C in the dark in perforated plastic bags. Cuttings that are transported in this way and rooted immediately after transport are more than 90% successful [8]. The possibility of prolonged storage of cuttings has been less often studied [24]. In our study, we evaluated the potential of expanded cold storage of unrooted pelargonium cuttings by analyzing numerous factors, such as variety, delivery time, and cold storage duration, as determined via the scale of professional production. Extending the storage period of unrooted pelargonium cuttings by up to two weeks using a more eco-friendly method may offer limited potential to influence market seasonality and could contribute modestly to improving the sustainability of pelargonium production. However, further studies are needed to confirm these possibilities.

Varieties of pelargonium differ in their storage sensitivity [13]. Genetic factors were very clearly visible in our research. Compared with those of the other peltatum varieties, the rooting efficiency of the P. zonale varieties decreased, and the rooting efficiency of the interspecific crosses exhibited intermediate differences. Similarly, Kutcher et al. [11] noted that the rooting of P. peltatum was marginally affected by prior storage in two tested genotypes of pelargonium.

Researchers have indicated the role of ethylene in reducing the quality of stored cuttings following problems with adventitious root formation [13,22]. Ethephon (a source of ethylene) is applied as a standard in stock plant production because it inhibits elongation and delays flower development; however, in excessive amounts, it can also limit rooting. In contrast, Druege et al. [25] and Darras et al. [26] demonstrated that ethylene stimulates rooting. We measured ethephon in pelargonium cuttings to assess its possible effect. Based on our observations, ethephon residues did not affect the quality of rooting. Mutui et al. [23] reported that short-term dark storage (4 days) reduced the ability of cuttings to continue growing regenerated roots and reduced both the number of roots per cutting and the length of the roots of the Pelargonium zonale ‘Katinka’. Subsequent studies have shown that dark storage does not have a negative effect on rooting or root quality [23]. Dark storage (4 days at 21 °C ± 1 °C) of pelargonium cuttings (P. zonale) can cause leaf yellowing due to stress-induced ethylene synthesis [23]. The chlorophyll a+b content also decreased in comparison with that in plants stored at the same temperature but in the light.

Our research also included nursery growing conditions and stock plant fertilization, which directly affect the nutritional status of the cuttings. There were differences in the nutritional status of the cuttings in both years, and a greater nitrogen supply was not conducive to rooting under cold storage. On the other hand, it has been reported that increased nitrogen availability positively affects rooting efficiency via the initiation of adventitious root development [27,28,29]. The results we obtained do not necessarily contradict these conclusions. In our work, the rooting process was prolonged by low temperature. Under conditions of slowed growth, the need for nitrogen is lower. A negative correlation was observed between nitrogen (N) levels and rooting efficiency, which can be attributed to the dominance of aboveground parts. When excessive nitrogen is present for the meristems, rooting becomes less effective [30]. When the amount of nitrogen accumulated in the inoculum is sufficient for normal plant metabolism, root formation is not initiated, as under conditions of full water coverage by fogging; those roots are simply redundant. This aspect has not been studied before in the context of rooting cuttings, but the functions of water and nutrient contents as factors shaping root system development have been well characterized [31]. This observation indicates an additional advantage of our suggested pelargonium cuttings production technology. Indeed, with the use of cold storage for planted cuttings, it is possible to reduce nitrogen fertilization in mother plants. During the summer/autumn months of 2022, stock plants experienced elevated temperatures and drought, which can be classified as a physiological stressor. Consequently, due to the suboptimal growth rate of the stock plants before harvesting, it was determined that an increase in nitrogen fertilization would enhance the growth rate. The analysis of the nutritional status of unrooted cuttings supported the application of this strategy.

The other factor that may have affected the rooting efficiency differences between the production seasons was the watering of the nursery plants. The Na⁺/K⁺ ratio increases in drought-treated plants [32,33]. The same was the case in our study, where an average increase in the Na⁺/K⁺ ratio was observed from 0.017 in 2020/21 to 0.023 in 2021/22. An indicator of the limited availability of water in the nursery during the 2021/22 season may also be the higher aluminum content of the cuttings [34]. Kutcher et al. [11] assumed that mild water stress could harden stock pelargonium plants and, thus, cuttings, and these plants would survive longer, which would increase rooting efficiency but with a simultaneous reduction in cutting yield. In our experiments, potential drought in the nursery was associated with a reduction in future rooting ability under conditions of cold storage of the stuck cuttings; thus, limiting watering cannot be recommended in the proposed improved production system. The opposite effect was observed by Kutcher et al. [11], which may be connected to both different rooting conditions (cold storage in our case) and the antagonistic effects of a higher nitrogen content in cuttings produced in 2021/22. In this case, the negative effect of a higher N supply would be stronger than the positive effect of mild drought hardening. However, our recent studies showed that simultaneous decreases in nitrogen supply and drought decrease rooting efficiency under cold storage conditions.

Based on our research, we propose an improved liner production system by applying sustainable practices, which are nowadays researched and required in ornamental plant production [15,35,36,37]. The limitation of nitrogen fertilization should be taken into account when managing the fertilization of stock plants. On the other hand, limited fertilization with elements such as Ca, Mg, Na, and K is not recommended. Adequate hydration of stock plants is necessary, as drought is not recommended if cuttings are intended for cold storage. After delivery to the farm, unrooted cuttings must be immediately placed in paperpots in plug trays and placed under conditions of high relative humidity (80–90%) and natural lighting (regulated with shading to 30 klx). The key is the correct temperature of 8/6 °C (day/night), which is a compromise between the quality of plants and their subsequent rooting efficiency, the length of storage and reduced costs of heating the greenhouse in the winter months. This temperature prevented the growth of the cuttings, which were stored for up to 2–4 weeks without a significant loss of rooting (depending on the variety).

The genetic factor should be considered when selecting the storage length. Varieties from the zonale group are more sensitive than those from the peltatum group and can be stored for approximately 2 weeks. In addition to genetic differences, the physiological state of the cuttings plays a crucial role in determining their storage potential. This can be monitored using chlorophyll fluorescence parameters, which have been shown to correlate with the rooting ability of pelargonium cuttings [38]. In our case, the SPAD measure was found to be uncorrelated with the nitrogen content of plants, while certain chlorophyll fluorescence transient parameters exhibited a correlation. This outcome is likely attributable to the pre-stressing of mother plants, a process that has been demonstrated to induce alterations in leaf anatomy. It is important to note that the SPAD index is sensitive to leaf thickness [39]. The findings of Rapacz et al. [38] highlight the importance of assessing the photochemical activity of the photosynthetic apparatus as a predictive marker for rooting success in stored cuttings. Cuttings can be systematically transferred from cold storage to liner production in a greenhouse heated to 20 °C. Such methods curtail the expenditure associated with full nutrition in the nursery and, above all, reduce the severe economic and environmental costs of heating the greenhouse to 20 °C in January. This system enhances the eco-efficiency of pelargonium production. The application of chemical retardants in the pelargonium nursery can be compensated for by the introduction of cooled stock cuttings in the greenhouse. Additionally, nitrogen nutrition may be reduced in the nursery. Therefore, cooling technology decreases the need for greenhouse heating. This technology makes it possible to balance the availability of cuttings and the demand for young plants, thus limiting the significant loss of commercial yield (the exact amount of which is a company secret), as overgrown plants are not readily purchased by buyers. The absence of such losses reduces the quantities of cuttings that need to be transported from the nursery and the greenhouse space required for production, all of which have further environmental benefits. The economic analysis highlights three key benefits of the new technology. First, it reduces the costs associated with the pelargonium stock plant production by decreasing its area without limiting production (cuttings) volume. Alternatively, the same area can be maintained to increase production, provided there is demand for the additional output. Second, it lowers the need for seasonal labor and improves the efficiency of internal labor (permanent employees) during the winter. This brings both economic advantages (reduced labor costs) and organizational benefits, as it simplifies training and ensures a balanced workload for employees during slower winter periods. The third benefit is environmental, as the reduction in the stock plant area cultivation by over 25% decreases water, chemical crop protection, and fertilizer use in Kenya, despite a 3% increase in cuttings imported to Poland.

5. Conclusions

Our study demonstrates that unrooted pelargonium cuttings can be effectively stored at reduced temperatures for up to 2 weeks without compromising rooting efficiency. Among the 24 pelargonium varieties tested, P. peltatum cultivars, particularly ‘VDP’, showed the best results, while P. zonale cuttings were most sensitive to cold storage. The success of storage relied on the quality and nutritional content of the stock plants, which varied between the two growing seasons and impacted rooting efficiency. Notably, higher nitrogen levels in the cuttings from 2021/22 reduced rooting success, particularly in P. zonale and interspecific hybrids. Harvest time and trace amounts of ethephon did not influence rooting outcomes. This method of cold storage, utilizing lower winter temperatures, can enhance large-scale cutting production, lower economic costs, improve labor efficiency, and slightly reduce the environmental impact of balcony plant nursery production.