RESTRICTING OVERHEAD IRRIGATION TO DAWN LIMITS GROWTH IN CONTAINER-GROWN WOODY ORNAMENTALS

Elaeagnus pungens Thunb., Ligustrum japonicum Thunb., Photinia x fraseri 'Red Top', and Rhododendron sp. 'Fashion' (azalea) growing in 10.4-liter containers were irrigated only at dawn with overhead impact sprinklers or pulse-irrigated three or four times each day with a drip system. Plant water potential was measured diurnally each week for 24 weeks, and growth was measured at the end of the growing season in December. Overhead irrigation resulted in less growth of all species than plants maintained near 100% container moisture with pulse irrigation. With the exception of photinia, more growth was associated with significantly lower daily accumulated water stress. Water stress of overhead-irrigated plants was generally not severe enough to cause stomatal closure.