Efficient water use is becoming increasingly important for horticultural operations to satisfy regulations regarding runoff along with adapting to the decreasing availability of water to agriculture. Generally, best management practices (BMPs) are used to conserve water. However, BMPs do not account for water requirements of plants. Soil moisture sensors can be used along with an automated irrigation system to irrigate when substrate volumetric water content (u) drops below a set threshold, allowing for precise irrigation control and improved water conservation compared with traditional irrigation practices. The objective of this research was to quantify growth of Hibiscus acetosella 'Panama Red' (PP#20,121) in response to various u thresholds. Experiments were performed in a greenhouse in Athens, GA, and on outdoor nursery pads in Watkinsville and Tifton, GA. Soil moisture sensors were used to maintain u above specific thresholds (0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, and 0.45 m 3 · m L3 ). Shoot dry weight increased from 7.3 to 58.8 g, 8.0 to 50.6 g, and from 3.9 to 35.9 g with increasing u thresholds from 0.10 to 0.45 m 3 · m L3 in the greenhouse, Watkinsville, and Tifton studies, respectively. Plant height also increased with increasing u threshold in all studies. Total irrigation volume increased with increasing u threshold from 1.9 to 41.6 L/plant, 0.06 to 23.0 L/plant, and 0.24 to 33.6 L/plant for the greenhouse, Watkinsville, and Tifton studies, respectively. Daily light integral (DLI) was found to be the most important factor influencing daily water use (DWU) in the greenhouse study; DWU was also found to be low on days with low DLI in nursery studies. In all studies, increased irrigation volume led to increased growth; however, water use efficiency (grams of shoot dry weight produced per liters of water used) decreased for u thresholds above 0.35 m 3 · m L3 . Results from the greenhouse and nursery studies indicate that sensor-controlled irrigation is feasible and that u thresholds can be adjusted to control plant growth.

Urban trees face a myriad of complex challenges growing in the built environment. The most common environmental conditions influencing urban tree mortality are water availability, nutrient deficiency and soil compaction. Long-term survival of recently installed trees has been directly attributed to site conditions, planting technique, and posttransplant maintenance. Tree survival is also dependent on selection of healthy, suitable plant material. Production methods for woody plants include traditional plastic containers (CG), pot-in-pot containers (PIP), and in-ground fabric containers (IGF). Alternatively, field grown trees may be produced as bare-root (BR) or root ball-excavated and burlapwrapped (B&B) trees. Each of these methods offers unique advantages in relation to production and installation. Many of the studies reviewed reveal varying post-transplant establishment and survival responses to production methods at a species-specific level.

Excessive irrigation and leaching are of increasing concern in container plant production. It can also necessitate multiple fertilizer applications, which is costly for growers. Our objective was to determine whether fertilizer and irrigation water can be applied more efficiently to reduce leachate volume and nutrient content without negatively impacting aboveground growth of Gardenia jasminoides ‘MAGDA I’. Plants were fertilized with one of three rates of a controlled-release fertilizer (subplots) (Florikan 18–6–8, 9–10 month release; 18.0N–2.6P–6.6K) [100 (40 g/plant), 50 (20 g/plant), and 25% of bag rate (10 g/plant)] and grown in 5.4-L containers outside for 137 days. Soil moisture sensor-controlled, automated irrigation was used to provide plants with one of four irrigation volumes (whole plots) (66, 100, 132, or 165 mL) at each irrigation event. All plants were irrigated when the control treatment (66 mL irrigation volume, 100% fertilizer treatment) reached a volumetric water content (VWC) of 0.35 m3·m−3. Plants in the different irrigation treatments were irrigated for 2, 3, 4, or 5 minutes, thus applying 66, 100, 132, or 165 mL/plant in the different irrigation treatments. Fertilizer rate had a greater effect on aboveground growth than irrigation volume with the 25% fertilizer rate resulting in significantly lower shoot dry weight (18.7 g/plant) than the 50% and 100% rates (25.3 and 27.3 g/plant respectively). Growth index was also lowest in the 25% fertilizer rate. Leachate volume varied greatly during the growing season due to rainfall and irrigation volume effects on leachate were most evident during the third, eighth, and ninth biweekly leachate collections, during which there was minimal or no rainfall. For these collections the control treatment of 66 mL resulted in minimal leachate (less than 130 mL over the 2-week leachate collection period), whereas leachate volume increased with increasing irrigation volumes. Pore water electrical conductivity (EC), leachate EC, NO3-N content, and PO4-P content were all highest with the 100% fertilizer rate, with the 66 mL irrigation treatment having the highest leachate EC for all fertilizer treatments. Cumulative leachate volumes for the 66 and 100 mL irrigation treatments were unaffected by fertilizer rate, whereas the 132 and 165 mL had greater leaching at the 25% fertilizer rate. Lower irrigation volumes resulted in reduced water and nutrient leaching and higher leachate EC. The higher leachate EC was the result of higher concentration of nutrients in less volume of leachate. The results of this study suggest that a combination of reduced fertilizer rates (up to 50%) and more efficient irrigation can be used to produce salable plants with reduced leaching and thus less environmental impact.

Additional index words. volumetric water content, nursery production, woody ornamentals, soil moisture sensor, container plants Abstract. Sustainable use of water resources is of increasing importance in container plant production as a result of decreasing water availability and an increasing number of laws and regulations regarding nursery runoff. Soil moisture sensor-controlled, automated irrigation can be used to irrigate when substrate volumetric water content (u) drops below a threshold, improving irrigation efficiency by applying water only as needed. We compared growth of two Gardenia jasminoides cultivars, slow-growing and challenging 'Radicans' and easier, fast-growing 'August Beauty', at various u thresholds. Our objective was to determine how irrigation can be applied more efficiently without negatively affecting plant quality, allowing for cultivar-specific guidelines. Soil moisture sensor-controlled, automated irrigation was used to maintain u thresholds of 0.20, 0.30, 0.40, or 0.50 m 3 · m L3 . Growth of both cultivars was related to u threshold, and patterns of growth were similar in both Watkinsville and Tifton, GA. High mortality was observed at the 0.20-m 3 · m L3 threshold with poor root establishment resulting from the low irrigation volume. Height, width, shoot dry weight, root dry weight, and leaf size were greater for the 0.40 and 0.50 m 3 · m L3 than the 0.20 and 0.30-m 3 · m L3 u thresholds. Irrigation volume increased with increasing u thresholds for both cultivars. For 'August Beauty', cumulative irrigation volume ranged from 0.96 to 63.21 L/plant in Tifton and 1.89 to 87.9 L/plant in Watkinsville. For 'Radicans', cumulative irrigation volume ranged from 1.32 to 126 L/plant in Tifton and from 1.38 to 261 L/plant in Watkinsville. There was a large irrigation volume difference between the 0.40 and 0.50-m 3 · m L3 u thresholds with little additional growth, suggesting that the additional irrigation applied led to overirrigation and leaching. Bud and flower number of 'Radicans' were greatest for the 0.40-m 3 · m L3 u threshold, indicating that overirrigation can reduce flowering. The results of this study show that growth of the different G. jasminoides cultivars responded similarly to u threshold at both locations. Similarities in growth and differences in irrigation volume at the 0.40 and 0.50-m 3 · m L3 u thresholds show that more efficient irrigation can be used without negatively impacting growth.

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