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A greenhouse study was conducted to quantify the irrigation requirements of two rose (Rosa hybrida L.) cultivars, RADrazz and Belinda’s Dream, which are widely valued for their ease of maintenance in landscapes, grown at four constant volumetric substrate moisture contents (SMCs) of 10%, 20%, 30%, and 40%. In both cultivars, there were no differences in growth and physiological responses between 30% and 40% SMC. In ‘RADrazz’, shoot dry weight (DW) was reduced by 25% and 86%, root DW was reduced by 27% and 71%, and flower number was reduced by 27% and 86% at 20% and 10% SMC, respectively, compared with 30% SMC. Midday leaf water potential (c), photosynthesis (Pn), stomatal conductance (gS), and transpiration (E) were highest at 30% and 40% SMC and they were lowest at 10% SMC. In ‘Belinda’s Dream’, shoot DW was reduced by 30% and 87%, root DW was reduced by 35% and 81%, and flower number was reduced by 42% and 75% at 20% and 10% SMC, respectively, compared with 30% SMC. Midday c was least negative at 40% SMC, whereas it was most negative at 10% SMC. There were no significant differences in midday c between 20% and 30% SMC. Pn, gS, and E were highest at 30% and 40% SMC and lowest at 10% SMC. In summary, plants at 30% and 40% SMC maintained the highest shoot and root DW, flower number, midday c, Pn, gS, and E. Water applied at 30% and 20% SMC was reduced by 31% and 70% compared with 40% SMC with excellent performance at 30% SMC and acceptable growth and quality at 20% SMC. The 10% SMC led to significant growth reduction, poor quality, and 25% mortality. Due to decreasing water resources and increasing population and urbanization, water conservation and development of more efficient irrigation systems are critical in greenhouse and landscape water management (Nicolas et al., 2008; Niu et al., 2006a). Additionally, many crops are overirrigated in greenhouse production, which results in runoff and leaching of water and nutrients from the greenhouse into the environment. To optimize water use in greenhouse production, a thorough understanding of the amount of water needed to produce quality plants is vital. Although water requirements of food crops and turfgrass have been enumerated, data quantifying the irrigation requirements of ornamental landscape plants are minimal at present. By irrigating plants based on water requirements, water use could be reduced, and plants may be acclimated for drought tolerance in the landscape (Kozlowski and Pallardy, 2002). Roses (Rosa hybrida L.) are some of the most popular garden plants in the world. RADrazz and Belinda’s Dream rose cultivars are well adapted to various climatic and soil conditions and provide the consumers with garden plants that require minimum fertilizer, water, and pesticides while growing in gardens or landscapes (Aggie Horticulture, 2014; MacKay et al., 2008). However, there is little science-based knowledge about the minimal irrigation required for plant growth and their responses to different SMC. Most drought studies use the drydown method to determine drought tolerance. In a cyclic drought study by Cai et al. (2012), ‘RADrazz’ and ‘Belinda’s Dream’ roses had significant reductions in Pn, gS, and E as SMC decreased from 20% to 10%. Plant responses to such cyclic drought stresses may differ from the responses to a continuous drought at stable SMC. The constant SMC can be maintained by the use of sensor technology in greenhouse production. Conserving water and reducing the environmental impact of runoff are two important issues confronting container production in greenhouses and nurseries (Warsaw et al., 2009). With increasing cost of water and stringent legislation, and decreasing water availability, the development of efficient irrigation technology that conserves water and reduces runoff without adversely affecting crop quality is becoming increasingly important for success of container nurseries. Applying irrigation based on plant water requirements is a key concept in water-conserving irrigation scheduling (Warsaw et al., 2009). Using a real-time sensing technology to detect the substrate water status and control irrigation is a promising approach for improving sustainability of irrigation management (van Iersel et al., 2010). The volumetric SMC is the most valuable environmental factor for automatic irrigation control (Jones, 2007). To study the growth and photosynthetic physiology of begonia (Begonia semperflorens L.) at six SMCs, Miralles-Crespo and van Iersel (2011) used time domain transmissometry sensors (TDTs) in multiple containers to control the irrigation based on container-specific SMC thresholds. The six SMCs ranged from 13.6% to 47.2%. The results showed that shoot DW of begonia increased as SMC increased, and plants had similar shoot DW at SMC higher than 34.8%. The total evapotranspiration increased linearly with SMC. With decreased SMC, begonia had significant reduction in leaf size, Pn, and gS (Miralles-Crespo and van Iersel, 2011). Burnett and van Iersel (2008) reported that there was an increase in water use efficiency and reduction in stem length and branch numbers of gaura (Gaura lindheimeri Engelm. & Gray) with decreasing SMC (45% to 10%). In a study by van Iersel et al. (2010), a substrate moisture sensor-controlled irrigation system was developed to quantify the daily water use of petunia (Petunia ·hybrida Hort ex. Vilm) in SMCs from 5% to 40%. Lower SMC resulted in a decrease in shoot DW, leaf y, and yS. There was only slight additional growth above 25% SMC. Similarly, at four constant SMCs (9%, 15%, 22%, and 32%), Nemali and van Iersel (2008) found that gas exchange, chlorophyll fluorescence, and leaf water potential were similar between 32% and 22% SMC for impatiens (Impatiens wallerana Hook.) and salvia (Salvia splendens Sell ex Roem. & Schult). The objectives of the current study were to determine minimum water requirements and quantify the growth and physiological responses of two popular landscape roses, ‘RADrazz’ and ‘Belinda’s Dream’, grown at four different SMCs using the TDT sensors in multiple containers to control the irrigation based on container-specific SMC thresholds. Received for publication 12 Mar. 2014. Accepted for publication 17 Apr. 2014. To whom reprint requests should be addressed; e-mail tstarman@tamu.edu. HORTSCIENCE VOL. 49(6) JUNE 2014 741 Materials and Methods Plant materials and culture. Rooted cuttings of two landscape rose cultivars, RADrazz and Belinda’s Dream, were purchased from Greenheart Farm (Greenheart, Arroyo Grande, CA) and transplanted to 23.5-L (28.1 cm wide, 45.7 cm long, 18.3 cm height) plastic containers (Iris USA Inc., Pleasant Prairie, WI) on 21 Jan. 2012 in a glass greenhouse at College Station, TX. Containers were filled with Fafard 52 mix (bark, Canadian sphagnum peatmoss, perlite, vermiculite, dolomitic limestone, wetting agent) (Fafard, Inc., Anderson, SC). The mix was evenly amended with 54 g of a slowrelease fertilizer, 15N-3.9P-9.9K Osmocote (Peters Professional, Scotts-Sierra, Marysville, OH). After transplanting, plants were manually irrigated with reverse osmosis (RO) water to container capacity and drenched evenly with broad-spectrum fungicide (Banrot ; Scotts-Sierra Crop Protection Company, Marysville, OH) until runoff to prevent root rot. During the establishment stage (35 d), plants were pruned once a week to remove flower buds and improve plant shape. Although the cultivars used for the study are relatively pest-free in the landscape, in this greenhouse study, plant foliage was washed with soapy water periodically to control spider mites. Greenhouse temperatures were controlled by a pad-and-fan cooling system during the summer and by a natural gas heating system during the winter. The average temperature in the greenhouse was 26.4 C day/22.0 C night, which was measured and logged by temperature sensors (HOBOs; Onset Computer Corp., Bourne, MA). The average daily light integral (DLI) and the average relative humidity (RH), measured using sensors (Watchdogs; Spectrum Technologies), were 27.5 mol·m·d and 70.0%, respectively. Irrigation system. The irrigation system consisted of Acclima TDT sensors (5.4 cm wide, 20.3 cm long, 1.4 cm height) (Acclima Inc., Meridian, ID), solenoid valves, and a polyethylene header pipe placed in the center and down the entire length of the bench. The Acclima TDT sensors were placed in the center of the container, lying flat. Two dribble ring emitters were placed on top of the root substrate and around the plants and secured with pins. Polyethylene pipe (Silver-line Plastics, Asheville, NC) was cut to fit between the header and each container and attached to the header with a tee fitting (Lasco Fittings Inc., Brownsville, TN). A 10-cm section of pipe was attached to each tee with a polyvinyl chloride threaded male adapter (Lasco Fittings Inc.) and Teflon tape (LG Sourcing Inc., North Wilkesboro, NC) that was attached to the solenoid valve (N-100F-H; Weathermatic, Dallas, TX). Containers were arranged as completed randomized design in two 3 · 1-m greenhouse benches with 51 cm between containers. Two dribble ring emitters (61 cm lead, 15 cm diameter) (Dramm Corporation, Manitowoc, WI) were evenly spaced and connected to the 25-cm polyethylene pipe by a microtube to deliver water to the plants. The garden hose was used to connect the system to a pressure regulator (25 PSI; Mister Landscaper, Dundee, FL) at the greenhouse water main faucet, which was the source of RO water. All sensors were placed and an extension cord (Chicago Electrical Power Tools, distributed by Harbor Freight Tools, Camarillo, CA) was cut into 86-cm pieces to connect each sensor. The irrigation system used in this greenhouse study measured SMC in multiple containers and irrigated the plants based on container-specific SMC thresholds. A laptop computer was connected to the irrigation system once a day to monitor the SMC and control for problems. When a sensor fails, the co

The Effect of Substrate Moisture Content on Growth and Physiological Responses of Two Landscape Roses (Rosa hybrida L.)