C.L. Wiese, A.L. Shober, E.F. Gilman, M. Paz, K.A. Moore, S.M. Scheiber, M.M. Brennan and S. Vyapari


Effects of Irrigation Frequency During Establishment on Growth of Ilex cornuta ‘Burfordii Nana’ and Pittosporum tobira ‘Variegata’

HortScience 44 (5): 1438-1443

Irrigation for establishing landscape plants is restricted to the first 60 days after planting by most water management districts in Florida, yet woody plants may require between 6 and 12 months to become established. Survival and growth of shrubs planted into landscapes depend on adequate irrigation until shrubs develop a root system capable of compensating for evapotranspiration losses. This study examined effect of irrigation frequency on survival, quality, and growth 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 3-month intervals for a total of 8 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 (12 to 22 WAP) and survival, quality, and growth were evaluated from that point through 104 WAP. Ilex cornuta 'Burfordii Nana' irrigated every 2 d had greater canopy growth index (52 through 88 weeks after planting (WAP)), canopy dry mass (52 and 104 WAP), and maximum root spread (20 through 64 and 88 WAP) when compared to shrubs irrigated every 8d in hardiness zone 8b. Pittosporum  tobira 'Variegata' irrigated every 2 d had greater canopy growth index (12 through 104 WAP), maximum root spread (20 through 28 and 64 through 88 WAP), and canopy dry mass (52 and 104 WAP) when compared to shrubs irrigated every 8 d 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 greater plant growth in zone 8b, the 2 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 18 months when plants showed visible signs of drought stress which occurred when there was no measurable rainfall for 30 consecutive days. 

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