Abstract
Production of attractive and water-efficient plants native to the plains and prairies of central North America can sometimes be limited because of problems associated with successful rooting of vegetative cuttings. Winecups (Callirhoe involucrata) is an attractive native plant, valued for its long period of bloom, drought tolerance, and winterhardiness, but can be difficult to propagate from seeds and vegetative cuttings. Seed dormancy issues can result in unreliable germination and seedling variations, which reduces crop uniformity. Although propagation from rooted cuttings maintains crop uniformity, cuttings often fail to root or root poorly. Manipulating the growing conditions of stock plants to suppress reproductive growth may improve rooting success of vegetative cuttings. Based on research conducted earlier with other ornamental perennials and programmed photoperiods, winecups plants were grown under three programmed photoperiods to determine if a particular photoperiod could be used to suppress reproductive growth and promote vegetative growth. The study consisted of three experiments, all conducted in similar fashion but at different times during the year. Results indicate that plants grown under 10-hour and 8-hour photoperiods remained vegetative longer when compared with plants grown under 12-hour photoperiod. Vegetative cuttings harvested from plants grown under 8-hour photoperiod had higher percent rooting when compared with vegetative cuttings harvested from plants grown under 10-hour and 12-hour photoperiods. Based on the findings from this research, plant propagators may be able to increase production of winecups by growing stock plants under 8-hour photoperiod.
Winecups is just one of the several common names for Callirhoe involucrata. Other common names include buffalo rose, copa de vino, cowboy rose, low poppy mallow, micoanujasqui, prairie winecups, purple poppy mallow, and wine cup(s) (Dorr 1990). Winecups is a hardy, low water requiring herbaceous perennial, native throughout the plains and prairies of the central United States, with populations also occurring in the Great Lakes Region, Pennsylvania, and Virginia, as well as farther west in the Pacific Northwest; south central Canada; and northern Mexico (Plant Select® 2009 and 2017; US Department of Agriculture, Natural Resource Conservation Service 2024). Bates et al. (1989) and Dorr (1990) have identified three naturally occurring varieties of winecups in North America: Callirhoe involucrata var. involucrata, Callirhoe involucrata var. lineariloba, and Callirhoe involucrata var. tenuissima, with the principal distinctions being geographical and morphological. Because of the variation that is known to exist, this species is considered a “polymorphic complex” (Bates et al. 1989).
Valued for its attractive growth, long period of bloom, drought tolerance, winterhardiness, and wide native range, winecups has become a highly desirable plant for the horticulture and landscape industries (Alberts and Mandel 2004; Plant Select® 2009, 2017, 2024). Propagation via seeds requires scarification of the hard seedcoat (Skogerboe 2001; Plant Select® 2009, 2017, 2024). However, because of the morphological differences associated with this species, propagators may want to propagate winecups vegetatively, rather than from seed, to maintain crop uniformity.
Vegetative propagation can be accomplished by micropropagation and cuttings. Micropropagation requires a sterile environment, and specialized growing media and supplies, whereas cutting propagation can be done in most greenhouses and does not require the specialized growing media and supplies. According to Hartmann et al. (2017), cutting propagation is the most important means for clonal regeneration of many horticultural crops, and successful cutting propagation requires development of adventitious roots. Studies have shown that efficient vegetative propagation can be achieved when stock plants are maintained in a juvenile or vegetative state of development, and that the presence of reproductive tissue can inhibit root development, resulting in failure of cuttings to produce roots (DeVier and Geneve 1997; Samarakoon and Faust 2022). As explained by Jackson (2009), juvenile plants do not respond to inductive stimuli that would be sufficient to induce flowering in an adult plant; and the juvenile phase can be as short as a few days in some herbaceous species or extend to several years in woody species. In many plant species, the juvenile-to-adult phase change is associated with phenotypical changes, such as alterations in leaf shape and/or leaf arrangement on the stem, as well as the production of flowers. In a study of 10 cultivars of chrysanthemum (Dendranthemum grandiflora), DeVier and Geneve (1997) found that root formation in cuttings was reduced as flowers developed on stock plants. In addition to the physiological state of the stock plants, rooting of vegetative cuttings may be impacted by rooting substrate (composition, nutrient concentration, temperature, and moisture), light (quantity, quality, and duration), and temperature; and can vary among cultivars of a species (Foster et al. 2017; Samarakoon and Faust 2022).
Adams and Langton (2005) noted that initiation of reproductive growth in plants is often regulated by photoperiod (the length of the light period in the diurnal cycle of 24 h). Photoperiod, as well as daily light integral (the number of photosynthetically active photons that are delivered to a specific area over a 24-h period), temperature, and plant hormones have all been shown to affect the length of the juvenile phase. Pallez Dole (2001) investigated the effects of photoperiod on the growth and quality of purple velvet plant (Gynura aurantiaca). Purple velvet plant is grown for its unique and attractive foliage; the purple color is actually due to the numerous deep purple trichomes that cover the leaves and stems. The inflorescences are malodorous heads of yellowish-orange disk florets that, when present, reduce plant quality and marketability. Pallez and Dole (2001) found that plants grown under 8-h photoperiod remained vegetative and had desirable plant quality. However, plants grown under 12-h and 16-h photoperiods developed reproductive growth, which reduced plant quality.
Rooting success of cuttings can be influenced by the photoperiod under which stock plants are grown. In a study involving three species of willows (Salix spp.), Moshkov and Kocherzhenko (1939) found that southern species grown under northern light conditions failed to reach the physiological state necessary for optimum rooting of cuttings unless they are grown with short day photoperiods. Moshkov and Kocherzhenko (1939) determined that the photoperiodic conditions experienced by a parent plant controls the rooting ability of cuttings harvest from that plant. In an investigation of the effects of photoperiod on the rooting of cuttings harvested from two cultivars of Siberian dogwood (Cornus alba), Whalley and Cockshull (1976) assessed the effects of four photoperiod treatments, and found that increased rooting occurred in cuttings obtained from Siberian dogwood plants grown under long-day photoperiod.
Only a few references regarding vegetative propagation of winecups could be located. Phillips (1995) indicates that winecups can be propagated from root cuttings that have at least one node or bud. Ryan (1998) notes that stem cuttings (3 to 4 inches long) harvested from winecups plants in early summer rooted quickly. Information on the Plant Select® website indicates varying rooting success with two-node stem cuttings harvested from young shoots, dipped in a 1:10 solution of a rooting hormone comprised of 1% indole-3-butyric acid and 0.5% 1-napthaleneacetic acid (Dip’N Grow, Inc., Clackamas, OR, USA), and placed under mist for 2 to 3 d. The contributor comments that sometimes there were “unacceptably high” losses due to unsuccessful rooting but provides no information pertaining to the physiological state of the stock plants from which cuttings were harvested (Plant Select® 2024).
In previous studies, Koski et al. (2024) found that when stock plants of ‘P009S’ twinspur, ‘Furman’s Red’ sage, and ‘Wild Thing’ sage were grown under photoperiods of 8 h, 10 h, and 12 h, the mean probability of rooting of cuttings harvested from those plants was significantly greater for cuttings harvested from plants grown under 10-h or 12-h photoperiods than for cuttings harvested from plants grown under 8-h photoperiod, and there was no significant difference in the mean probability of rooting of cuttings between cuttings harvest from plants grown under 10-h or 12-h photoperiods.
To learn more about the effects of the stock plants in the vegetative production of winecups, a study was conducted at Colorado State University (CSU) Horticulture Center (Fort Collins, CO, USA; lat. 40.5703°N, long. 105.0903°W) that began in Apr 2023. The purpose of this study was to determine if photoperiod regulation could be used to suppress reproductive growth by promoting vegetative growth in winecups stock plants, thereby enhancing rooting of cuttings harvested from those stock plants.
Materials and methods
Three experiments were conducted: Expt. 1 was started 12 Apr 2023, Expt. 2 was started 16 Jun 2023, and Expt. 3 was started 13 Nov 2023. The three experiments could not be conducted simultaneously because we had only three grow tents, and each of the three photoperiod treatments required one grow tent.
Photoperiod treatment areas
The study was conducted in a greenhouse at CSU Horticulture Center. The ambient photoperiod treatment was conducted on a greenhouse bench, and the three programmed photoperiod treatments [12 h light (12 h), 10 h light (10 h), and 8 h light (8 h)] were conducted in 4-feet × 8-feet × 8-feet grow tents (Gorilla Grow Tent, Santa Rosa, CA, USA) set up in the same greenhouse with the ambient light treatment. Each photoperiod treatment area was equipped with a digital thermometer (AcuRite, Lake Geneva, WI, USA) that provided minimum, maximum, and current temperatures, which were recorded daily or at least several times each week. Each grow tent was also equipped with two light-emitting diode (LED) lights (Philips Toplighting Linear GPL DR/W MB 200 400 V, Signify Netherlands, Eindhoven, North Brabant, Netherlands), two 4-inch 165-ft3/min inline fans (Active Air, Hydrofarm, Shoemakersville, PA, USA), and one three-speed floor fan (Home Depot, Atlanta, GA, USA). The linear LED lights were used because they were available at the Horticulture Center. LED lights were positioned ∼52 inches above the bench on which the plants were grown. The inline fans helped to remove hot air from within the grow tents. The floor fan helped to circulate air within the grow tents. The 12-h, 10-h, and 8-h photoperiod treatments were each assigned to one of the three grow tents. Within each grow tent, the linear LED lights were programmed with a mechanical timer (Apollo® 10-240v 10A; Titan Controls®, Angleton, TX, USA). Each photoperiod treatment was assigned to its grow tent for the duration of the study.
Plants
The winecups plants used in each experiment were young plants (less than 6 months old) either grown from seed or rooted cuttings and obtained from different sources (due to availability at the time each experiment was initiated). Plants for Expt. 1 were young plants grown from seed in a 72-cell tray and obtained from a local greenhouse (Gulley Greenhouse, Fort Collins, CO, USA) on 23 Mar 2023. Plants for Expt. 2 were young plants grown from seed and dug from a local garden on 24 May 2023. Plants for Expt. 3 were young plants grown from seed and transplanted into black plastic containers (2.5 inches × 2.5 inches × 3.5 inches) arranged in 32-cell trays and obtained from a local greenhouse (Kiyota Greenhouse, Fort Lupton, CO, USA) on 10 Nov 2023. For each experiment, the young plants were transplanted into black plastic containers (4 inches × 4 inches × 5 inches) filled with growing medium composed of coarse grade peatmoss, coarse grade perlite, dolomitic and calcitic limestone, and nonionic wetting agent (Berger BM6 HD; Berger, Saint-Modeste, QC, Canada). In each experiment, 32 containers were prepared and then divided equally among four photoperiod treatment areas, with eight replications per treatment. After plugs were transplanted into the containers, each container was labeled, and placed in a 15-cell square pot carry tray (one tray for each of the four photoperiod treatment areas).
The height (H) and two widths (W1 and W2) were measured (in centimeters) for each plant; these measurements were then used to generate a beginning size index for each plant [(H+W1+W2)/3]. The trays of labeled containers were then placed into their assigned photoperiod treatment area. While in their photoperiod treatment areas, plants were watered with a solution of 20N–4.4P–16.6K diluted to a concentration of 100 parts per million N (Greencare Fertilizers, Inc., Kankakee, IL, USA). At each irrigation event, 250 mL of fertilizer solution was applied to each container. To better understand when containers needed to be watered, a soil moisture sensor (Theta Probe, Delta-T Devices Ltd, Burwell, Cambridgeshire, England) was used to determine growing medium moisture. Growing medium moisture measurements were taken two to three times each week to assess moisture content in the growing medium, and to determine when a container needed to be watered. When soil moisture percentage was 15% or less, that container was given 250 mL of fertilizer solution.
Plants were in assigned photoperiod treatment areas for 11 weeks for Expt. 1 (12 Apr 2023 to 28 Jun 2023), 18 weeks for Expt. 2 (19 Jun 2023 to 26 Oct 2023), and 9 weeks for Expt. 3 (13 Nov 2023 to 17 Jan 2024). Each plant was observed weekly for signs of reproductive growth. Onset of reproductive growth was affirmed when a flower bud first became visible in the terminal growth of a stem. The date that reproductive growth was first observed on a plant was recorded on a data sheet. Observations continued weekly for all plants in each photoperiod treatment area. An experiment was concluded when all (or most) of the plants in any one of the programmed photoperiod treatment areas (12 h, 10 h, or 8 h) exhibited reproductive growth, or after plants had been in photoperiod treatment areas for 18 weeks (Expt. 2). At the conclusion of each experiment, each replicate in each photoperiod treatment area was remeasured to obtain an ending size index. Growth rates, calculated as centimeters per week, were calculated as the difference between ending and starting size indices divided by the number of weeks separating measurements. Subsequently, five of eight plants in each experiment were harvested, placed in labeled paper bags, and weighed (in grams) using an analytical balance (Ohaus Corporation, Parsippany, NJ, USA), then dried in a drying oven (Despatch, Minneapolis, MN, USA) at 70 °C for 72 h. Dried plants (in their paper bags) were reweighed after removal from drying oven. Medial vegetative cuttings (each containing two nodes and ∼5 to 7 cm in length) were clipped from the unharvested plants in each photoperiod treatment, and 24 cuttings from plants in each photoperiod treatment area were dipped into a 1:19 solution of a rooting hormone composed of 1% indole-3-butyric acid and 0.5% 1-napthaleneacetic acid (Dip’N Grow) for 15 s before being stuck into a moistened 72-cell rooting tray (Jiffy Preforma; Jiffy Products of America, Inc., Lorain, OH, USA). The trays of cuttings were then placed on a bench equipped with a heat mat set at 72 °F, and misting system initially programmed to deliver 8 s of mist every 30 min. After 2 weeks, the misting time was adjusted to 8 s every 60 min. The plants from which the cuttings were obtained were then cut back to a height of ∼4 cm, allowed to regrow in their assigned photoperiod treatment area, and again observed for production of reproductive growth. The stuck cuttings were observed weekly for rooting for 4 weeks.
Statistical analysis
The data for the three experiments were combined for statistical analysis. Linear mixed models were fit to observations of the duration of vegetative growth (weeks), growth rate (centimeter/week), and final dry weight (grams). Photoperiod treatments and experimental repeats were modeled as fixed and random effects, respectively. For significant fixed effects, mean separation was performed using Tukey’s honestly significant difference. For harvested cuttings, a logistic model was fit to binary observations of the absence (0) or presence (1) of roots over time with similar fixed and random effects, but the model contained an additional continuous variable indicating the elapsed time (days) after sticking cuttings. Analysis of deviance was used to analyze the cutting rooting data; this measures the discrepancy between the current model and a model that fits the data perfectly. A smaller deviance indicates a better model fit. Means comparison was performed by computing the probability of rooting, averaged over time, for a given fixed effect. The data were analyzed using R (R Core Team 2021).
Results
Can photoperiod regulation be used to suppress reproductive growth by promoting vegetative growth in winecups stock plants, thereby enhancing rooting of cuttings harvested from those stock plants? Although the length of the programmed photoperiod treatments (12 h, 10 h, and 8 h) remained constant, the conditions in the ambient light treatment area varied with each experiment. Because of the variability associated with the ambient light treatment area, we focus primarily on the results from the three programmed photoperiod treatments. Analysis of variance (ANOVA) indicates that photoperiod treatments significantly affected duration of vegetative growth (P < 0.001), growth rate (P < 0.001), and ending dry weight (P = 0.009) (Table 1). Analysis of deviance indicates that photoperiod treatments significantly affected probability of cutting rooting (P < 0.001) (Table 2). The key findings indicate that stock plants grown under 8-h photoperiod remained vegetative for a longer time, and had lower ending dry weights, when compared with stock plants grown under 12-h photoperiod.
ANOVA of effects of photoperiod treatments on duration of vegetative growth, growth rate, and ending dry weight of winecups plants (three experiments combined).
Analysis of deviance of the probability of rooting of cuttings harvested from winecups grown under different photoperiods (three experiments combined).
Temperatures within photoperiod treatment areas
Although the study was conducted in a greenhouse, and the three programmed photoperiod treatments were conducted in grow tents set up inside the greenhouse, temperatures within photoperiod treatment areas varied depending on the time of year the experiments were conducted (Table 3). During Expt. 1 (conducted 15 Apr 2023 to 28 Jun 2023), mean maximum temperatures inside grow tents ranged from 88.5 to 90.8 °F; higher than mean maximum temperatures inside grow tents during Expts. 2 and 3. During Expt. 2 (conducted 19 Jun 2023 to 26 Oct 2023) mean maximum temperatures inside grow tents ranged from 85.8 to 88.1 °F, and during Expt. 3 (conducted 13 Nov 2023 to 17 Jan 2024) mean maximum temperatures inside grow tents ranged from 73.4 to 74.8 °F (Table 1). Based on local temperature data (Colorado Climate Center, Fort Collins, CO, USA) outside mean maximum temperature during Expts. 1, 2, and 3 was 59.5 °F, 66.8 °F, and 32.6 °F, respectively, and maximum temperature ranges during Expts. 1, 2, and 3 were 32 to 78 °F, 41 to 81 °F, and −4 to 50 °F, respectively. Inside temperatures appeared to have been somewhat affected by outside temperatures, as indicated by the lower temperatures recorded both inside and outside during Expt. 3. It is unclear as to how temperatures affected duration of vegetative growth, growth rate, and dry weight of stock plants grown under the different photoperiods.
Mean temperature and range of temperatures for each experiment within each photoperiod treatment area of winecups photoperiod study.
Duration of vegetative growth
When data for the three experiments were combined, plants grown under 10-h and 8-h photoperiods had significantly longer mean duration of vegetative growth (8.71 weeks and 9.17 weeks, respectively) when compared with plants grown under 12-h photoperiod (6.58 weeks) (Table 4).
Comparison of duration of vegetative growth, growth rate, and ending dry weight for winecups plants grown under different photoperiods (three experiments combined).
Growth rates
Growth rate was calculated as the difference between ending size index and beginning size index divided by the elapsed time between the measurement of the ending size index and the measurement of the beginning size index {[size index(time2) – size index(time1)]/elapsed time between time1 and time2}. When data for the three experiments were combined, plants grown under 10-h and 8-h photoperiods had significantly smaller mean growth rates (8.87 cm per week and 10.81 cm per week, respectively) when compared with plants grown under 12-h photoperiod (18.51 cm per week) (Table 4).
Ending dry weights
When data for the three experiments were combined, plants grown under 12-h photoperiod had significantly greater mean ending dry weight (5.19 g) when compared with plants grown under 10-h and 8-h photoperiods (3.02 g and 3.38 g, respectively) (Table 4).
Rooting of cuttings
At the observation level, rooting was recorded as a binary variable, where 0 was assigned to “not rooted” (no), and 1 was assigned to “rooted” (yes). The data follow a Bernoulli distribution (Encyclopedia of Mathematics 2020) in which the discrete probability distribution of a random variable is given the value of 0 if no and the value of 1 if yes. Because these types of data do not meet the assumption for ANOVA that data are normally distributed, the standard ANOVA to test effects and separate means could not be used. The most common approach to fitting models to binary data are to use logistic regression, which produces unfamiliar coefficients representing the log-odds of a change in outcome (unrooted/rooted) for each experimental treatment, and the log-odds are often converted to odds ratios or probabilities, which are more easily understood. As indicated in Table 5, the effect of photoperiod treatments on stock plants significantly impacted the probability of rooting of cuttings. Cuttings harvested from plants grown under an 8-h photoperiod had significantly higher probability of rooting (0.78) when compared with cuttings harvested from plants grown under 12-h and 10-h photoperiods (0.63 and 0.52, respectively).
Comparison of probability of rooting of cuttings harvested from winecups plants grown under different photoperiods within 28 d after sticking (three experiments combined).
Discussion
Foster et al. (2017), in their studies on the propagation of twinflower (Linnaea borealis), noted that the source of cuttings impacted quality of rooting. Several studies have correlated reduced root formation when cuttings are obtained from plants exhibiting reproductive growth (DeVier and Geneve 1997; Dole and Gibson 2006; Pallez and Dole 2001; Samarakoon and Faust 2022). In this study, which investigated the effects of programmed photoperiods on the growth of winecups, and the cuttings harvested from those plants, we found that plants grown under 8-h photoperiod tended to remain vegetative longer when compared with plants grown under longer photoperiods. This finding is in agreement with Pallez and Dole (2001), who found that purple velvet plants grown under 8-h photoperiod remained vegetative and produced foliage with the brightest purple color, and produced the greatest number of vegetative shoots when compared with plants grown under 12- or 16-h photoperiods.
We observed differences among the winecups plants in the three experiments. In Expt. 1, four of the plants grown under 10-h photoperiod produced reproductive growth by the fourth week of photoperiod treatments, but then stopped producing reproductive growth by the 11th week, and the remaining four plants remained vegetative even after the 11th week. Similarly, in Expt. 1, four plants grown under 8-h photoperiods produced reproductive growth by the fourth week of photoperiod treatments, but all plants had stopped producing reproductive growth by the 11th week. In Expt. 3 only one of the plants grown under 10-h photoperiod developed reproductive growth, and none of the plants grown under 8-h photoperiod developed reproductive growth during the 10 weeks the photoperiod treatments were applied. Something was different in Expt. 2. Even after 11 weeks under the photoperiod treatments, none of the plants in Expt. 2 developed reproductive growth. We are uncertain as to why plants in the three experiments responded differently to the photoperiod treatments; however, the plants used in the three experiments were obtained from different sources and at different times of the year. As indicated by Raihan et al. (2021), plant vegetative phase transition is influenced by numerous epigenetic factors; external environmental stimuli interact with internal cues that in turn regulate gene expression. However exactly how these interactions alter gene expression and influence phase transition is still not well understood. The greater dry weights of winecups plants grown under 12-h photoperiod (Table 4) are reported to be a common occurrence. As noted by Adams and Langton (2005), there have been numerous reports that when plants are grown under long-day photoperiod (photoperiod greater than 12 h of light), the dry weight of aboveground parts of the plant increases. Over the years, researchers and plant propagators have noted that the rooting ability of cuttings harvested from various species of herbaceous and woody plants often shows seasonal variation, and as well as variations of species within a genus (Whalley and Cockshull 1976). Foster et al. (2017) noted that previous research demonstrates that rooting may be affected by a variety of environmental factors, including light, substrate moisture, and nutrient concentration. Roll and Newman (1997) showed that the photoperiod under which stock plants of poinsettia (Euphorbia pulcherrima) were grown influenced the rooting of cuttings harvested from those stock plants. The authors concluded that using a night break to prevent flower initiation of stock plants produced higher-quality cuttings when propagation took place after the critical daylength for flowering had passed. Torres and Lopez (2011) found a similar response with yellow trumpet bush (Tecoma stans); plants grown under photoperiods of 12 h or less produced fewer flower buds when compared with plants grown under photoperiods of 14 h or greater. Among the three experiments, we did observe differences in cutting rooting success. For plants grown in Expt. 1, there was no difference in mean percent rooting of cuttings harvested from plants grown under 12-h, 10-h, and 8-h photoperiods, 95.8% for all three photoperiods When compared across the three experiments, in Expt. 1, mean percent rooting of cuttings was the same (98.5%) for all programmed photoperiods, even though at the time of cutting harvest, all eight of the plants grown under 12-h photoperiod were reproductive, but none of the plants grown under 10-h and 8-h photoperiods were reproductive. When compared across the three experiments, in Expt. 2, mean percent rooting of cuttings harvested from plants grown under 12-h, 10-h, and 8-h photoperiods were 95.8%, 91.7%, and 100.0%, respectively, even though none of the plants grown under any of the programmed photoperiods were reproductive. When compared across the three experiments, in Expt. 3, mean percent rooting of cuttings was noticeably lower for cuttings harvested from plants grown under 12-h and 10-h photoperiods (66.7% and 66.7%, respectively), but not for cuttings harvested from plants grown under 8-h photoperiod, where cutting rooting was 95.8% (Table 6). Although it might be assumed that the primary reason for this lower rooting success was attributed to the presence of reproductive growth in the plants grown under 12-h and 10-h photoperiods, we cannot make this assumption because although reproductive growth was present in all eight (100%) of the plants grown under 12-h photoperiod, reproductive growth was present in only one (12.5%) of the plants grown under 10-h photoperiod. Thus it appears that the presence of reproductive growth is just one of possibly several factors that affect cutting rooting. This thought is supported by Dole and Gibson (2006), who in addition to cutting quality, note that environmental conditions associated with temperature and light can greatly affect cutting rooting success. In our study, we found that when winecups plants were grown under 8-h photoperiod, reproductive growth was suppressed and cutting rooting improved (Tables 4 and 5). Although we did not directly assess root quality, we did observe that the roots produced on cuttings harvested from plants grown under 8-h photoperiod were thicker when compared with the roots produced on cuttings harvested from stock plants grown under 10-h and 12-h photoperiods. Based on the findings from this research, plant propagators may be able to increase production of winecups by growing stock plants under 8-h photoperiod.
Percent rooting of cuttings 4 weeks after sticking cuttings harvested from winecups stock plants grown under different photoperiods and dates.
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