APS_JANUARY2024

E lderberry

17

base. For each container, four canes per plant were selected and pruned to 50 cm above the potting medium surface. All other canes were removed at the potting medium surface. All plants were then placed back under the poly ethylene foam blanket and plastic sheeting for frost protection until air temperatures were consistently above 0 °C. Elderberry plants were uncovered, and six replications of each treatment were arranged in a randomized complete block design in the nursery area on 3 May 2022 after the danger of frost was past. All plants were fertilized with 50 g 15N-9P-12K controlled-release fertilizer (Osmocote®; Scotts Company, Marysville, OH) per container. Plants were subsequently grown under natural conditions with supple mental drip irrigation beginning in mid-May and adjusted as needed. New shoot growth that occurred on plants after 4 Apr 2022 was measured and all shoot growth was harvested at the surface of the pot ting medium for dry weight measurement on 6 Sep 2022. The following day, all roots from each container were washed free of potting media. Root and shoot tissue were oven-dried at 65 °C for 48 h to obtain their dry weights. On 1 Nov 2022, two-year-old American el derberry plants were obtained from the same nursery. Experimental methods and data re corded were similar to those previously de scribed. Additionally, fruit was harvested at peak ripeness (i.e., all drupes dark purple) in August. After de-stemming, fruit number and fresh weight per plant were recorded. Meteorological data were recorded using an environmental monitoring system (U30; On set, Bourne, MA) located 1 m from the pot ted elderberry plants. Mean maximum daily temperatures, as well as mean daily solar ra diation, were calculated for each month from Apr through Aug in 2022 and 2023, and total monthly precipitation for the same period was recorded. Data were analyzed using PROC GLIM MIX in SAS (SAS Institute, Cary, NC). Shoot growth and root and shoot dry weights were analyzed as a factorial arrangement of treat

ments (2 years x 2 root pruning treatments x 2 transplanting treatments). Because of the lack of flowering and fruiting in 2022 of all treat ments and the failure of the RP + NT-treated plants to bloom in 2023, fruit number and fruit weight data were subjected to a one-way anal ysis of variance (ANOVA) using the PROC GLIMMIX statement in SAS (SAS Institute, Cary, NC). Means were separated by Fisher’s protected least significant difference (LSD) test, P < 0.05. Results In Apr, May, and Jun 2022, the mean maxi mum daily temperatures were 2.7, 1.8, and 0.6 °C cooler, respectively, than temperatures recorded for these same months in 2023 (Ta ble 1). However, the mean maximum daily temperatures for Jul and Aug 2022 were 0.6 and 1.8 °C warmer than those of respective months in 2023. Before bloom and during flowering in May and Jun 2022, there was less solar radiation compared with that time period in 2023 (Table 1). There was higher precipita tion in Apr and May 2022 than in 2023 but more rainfall was recorded in Jun, Jul, and Aug 2023 than in the same months of 2022 (Table 1). Plant growth responses to treatments. The three-way interaction of year x root pruning x transplanting was significant for new shoot growth and total shoot dry weight ( P = 0.001 and P < 0.001, respectively) (Table 2). Shoot growth and dry weight for each treatment combination were always less in 2022 than in 2023 (Table 2). For each year, the RP + NT treatment reduced shoot growth by 38.8% in 2022 and 25.5% in 2023, respectively, com pared with the NRP + T treatment. Although the NRP + NT had more shoot growth than the RP + NT treatment, it partially controlled shoot vigor when compared with plants that were transplanted. For each year, shoot dry weight was the least for the RP +NT treatment and greatest for the NRP + T treatment (Table 1). In 2022, NRP + NT and RP + T treatments had similar shoot dry weights, but they were greater than