Abstract

Effects of irrigation frequency during establishment on the growth of Ilex cornuta 'Burfordii Nana'and Pittosporum tobira 'Variegata'. 2009. Wiese, C.L., A.L. Shober, E.F. Gilman, M. Paz, K.A. Moore, S.M. Scheiber, M.M. Brennan, and S. Vyapari. HortScience. In Press.

Survival and growth of shrubs planted into the landscape depend on adequate irrigation until shrubs develop a root system that is able to compensate for evapotranspiration losses. This study examined the effect of irrigation frequency on survival, quality, canopy growth index, root spread radius, root spread to canopy spread ratio, dry root mass, and dry shoot mass of Ilex cornuta Lindl. & Paxt. 'Burfordii Nana' and Pittosporum tobira [Dryand] 'Variegata' planted in north (Citra, FL; USDA hardiness zone 8b) and central (Balm, FL; hardiness zone 9b) Florida. Shrubs were planted into the landscape from 11.4 L (#3) containers at three month intervals for a total of eight planting dates over 2 years and irrigated every 2, 4, or 8 d with 3 L of water at each irrigation event. Scheduled irrigation was discontinued once roots grew to the canopy edge. Ilex cornuta 'Burfordii Nana' irrigated every 2 d had greater canopy growth index (52 to 88 weeks after planting (WAP)), canopy dry mass (52 and 104 WAP), and root spread (20 to 64 and 88 WAP) than shrubs irrigated every 8d in hardiness zone 8b. Pittosporum tobira 'Variegata' irrigated every 2 d had greater canopy growth index (12 to 104 WAP), root spread (20 to 28 and 64 to 88 WAP), and canopy dry mass (52 and 104 WAP) than shrubs irrigated every 8d in hardiness zone 8b. However, there were no differences in shoot or root growth due to irrigation frequency for these shrubs planted in hardiness zone 9a. Irrigation frequency did not affect shrub survival or aesthetic quality at either location. Although more frequent irrigation (every 2 d) resulted in more plant growth in zone 8b, the two shrub species tested survived and grew after planting in hardiness zones 8b and 9a on natural rainfall alone provided they were irrigated during establishment with 3 L every 4 to 8 d until roots reached the canopy edge. Subsequent supplemental irrigation was only needed in the following 6 months when plants show visible signs of drought stress and there was no measurable rainfall for 30 consecutive days.