The 2010 ASHS Annual Conference

Rooted cuttings of Viburnum odoratissimum were grown outdoors to market size in 11.4-L containers.  Actual evapotranspiration (ET_A) of nine plants was determined daily, along with evaporation from three control containers shaded by plastic foliage to mimic plant growth. The first 60 days after transplanting, substrate evaporation accounted for most of ET_A.  Substrate evaporation was generally constant the first 160 days before declining, but still remained around 160 mL/day through harvest at market size.  ET_A increased with growth and generally followed variations in reference evapotranspiration (ETo).  Mean ET_A during most of the production cycle was less than 600 mL/day (11.8 mm based on upper container surface area).  With the spring growth flush, mean ET_A reached 1.3 L/day as plants achieved market size.  Mean cumulative ET_A to produce 90% of measured plants to market size was 155 L or 3.1 m depth per plant based on container surface area.  Water need indices, similar to crop coefficients, were highly correlated with percent canopy closure.  This correlation offers a straight forward method to model shrub irrigation requirements based on plant size, spacing and ETo.