Salt-tolerant landscape plants are important to ornamental growers, landscapers, and residents in coastal communities. Ornamental grasses are frequently recommended for low-maintenance landscape situations and may be candidates for coastal plantings after they are evaluated for their salt spray tolerance. ‘Gracillimus’ maiden grass (Miscanthus sinensis) and ‘Hamelin’ fountain grass (Pennisetum alopecuroides) were subjected to four treatments [100% seawater salt spray, 50% seawater salt spray, 25% seawater salt spray, or 0% seawater salt spray (100% deionized water)] applied as a foliar spray. As seawater concentration increased, root, shoot, whole-plant biomass gain, height, inflorescence number, and visual quality decreased for both cultivars; however, fountain grass appears to be slightly more tolerant of salt spray than maiden grass.
Although new and innovative measures to reduce landscape water consumption are being sought, traditional methods of water restrictions and plant selection prevail. Species native to North America are often promoted as drought tolerant with little information to support or refute such claims. Furthermore, species performance is unknown in maintained environments such as commercial and residential landscapes. Thus, 10 native and 10 exotic species, commonly used in landscapes, were evaluated independently for postestablishment growth and aesthetics under irrigated and nonirrigated landscape conditions. Growth indices were recorded monthly, with dieback and plant density evaluated at termination of the experiment. At termination of the experiment, canopy size of eight native [beautyberry (Callicarpa americana), fringe tree (Chionanthus virginicus), yaupon holly (Ilex vomitoria ‘Nana’), virginia sweetspire (Itea virginica), wax myrtle (Myrica cerifera), chickasaw plum (Prunus angustifolia), saw palmetto (Serenoa repens), and coontie (Zamia floridana)] and eight exotic [golden dewdrop (Duranta erecta), cape jasmine (Gardenia augusta), crape myrtle (Lagerstroemia indica), oleander (Nerium oleander), japanese pittosporum (Pittosporum tobira), indian hawthorn (Rhaphiolepis indica), sweet viburnum (Viburnum odoratissimum), and sandankwa viburnum (V. suspensum)] species were similar for irrigated and nonirrigated treatments. Irrigation resulted in larger canopy sizes for two native [walter's viburnum (V. obovatum) and inkberry (I. glabra)] and two nonnative [japanese privet (Ligustrum japonicum) and fringe flower (Loropetalum chinensis)] species. Among the native species with larger canopy sizes under irrigated conditions, all are indigenous to swamps and streams. With the exception of virginia sweetspire, plant density and dieback were similar for irrigated and nonirrigated plants of all taxa examined. Irrigated virginia sweetspire plants had higher plant density and dieback ratings than nonirrigated plants. Results indicate that, aesthetically, irrigated and nonirrigated plants were similar. Data emphasize the importance of selecting plant material adapted to existing environmental landscape conditions.
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 the 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; USDA hardiness zone 9b) Florida. Shrubs were planted into the landscape from 11.4-L (#3) containers at 3-month intervals for a total of eight planting dates over 2 years and irrigated every 2, 4, or 8 days with 3 L of water at each irrigation event. Scheduled irrigation was discontinued once roots grew to the canopy edge [12 to 22 weeks after planting (WAP)] and survival, quality, and growth were evaluated from that point through 104 WAP. Ilex cornuta ‘Burfordii Nana’ irrigated every 2 days had greater canopy growth index (52 through 88 WAP), canopy dry mass (52 and 104 WAP), and maximum root spread (20 through 64 and 88 WAP) when compared with shrubs irrigated every 8d in hardiness zone 8b. Pittosporum tobira ‘Variegata’ irrigated every 2 days 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 with shrubs irrigated every 8 days in hardiness zone 8b. However, there were no differences in shoot or root growth resulting from 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 days) resulted in greater 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 days 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.
The survival and quality of shrubs planted in the landscape from containers is dependent on irrigation to ensure the development of a healthy root system. This study determined the effect of irrigation frequency on survival, quality, canopy growth index, root to canopy spread ratio, and dry root and shoot biomass of Viburnum odoratissimum Ker-Gawl. (sweet viburnum) planted in Florida in USDA hardiness Zones 8b (Citra, FL), 9a (Balm, FL), and 10b (Ft. Lauderdale, FL). Sweet viburnum shrubs were planted into the landscape from 11.4-L (#3) containers and irrigated with 3 L every 2, 4, or 8 days. Shrubs were planted on eight dates over a 2-year period (2004 to 2006). Irrigation frequency during the 12- to 22-week irrigation period had no significant effect on sweet viburnum survival or aesthetic quality at any location. In addition, there was no irrigation effect on root spread, root to shoot biomass ratio, or root biomass for shrubs planted in Zones 8b or 9a. However, sweet viburnum irrigated every 2 days had greater canopy growth index at 28 and 104 weeks after planting than shrubs irrigated every 4 or 8 days in Zone 8b and every 8 days in Zone 9a. When planted in Zone 10b, sweet viburnum irrigated every 2 days exhibited greater growth index, shoot biomass, and root biomass than plant receiving irrigation every 4 days. Although more frequent irrigation (every 2 days) resulted in more plant growth in Zones 8b and 10b, sweet viburnum survived and grew after planting under natural rainfall conditions provided they were irrigated with 3 L of water every 8 days during establishment until roots reached the canopy edge in hardiness Zones 8b and 9a and every 4 days in hardiness Zone 10b. Subsequent supplemental irrigation (hand-watering) was only needed after irrigation was ended when plants exhibited visible signs of drought stress and there was no measurable rainfall for 30 consecutive days.
The survival of shrubs planted into the landscape depends on sufficient irrigation during the establishment period. Few studies have investigated the effect of irrigation frequency on the posttransplant growth of landscape shrubs. We conducted two studies in U.S. Department of Agriculture hardiness zone 10b over a 2-year period in which we compared canopy growth index (GI), root extension to canopy spread ratio, canopy dry weight, and root dry weight of shrubs irrigated at different frequencies. In the first experiment, wild coffee (Psychotria nervosa) and ‘Lakeview’ orange jasmine (Murraya paniculata) shrubs were planted in Sept. 2004, Dec. 2004, Mar. 2005, and June 2005 and irrigated for 28 weeks after planting (WAP) every 2, 4, or 8 days with 3 L of water per irrigation event. In the second experiment, ‘Macafeeana’ copperleaf (Acalypha wilkesiana) and orange jasmine shrubs were planted in Sept. 2005, Dec. 2005, Mar. 2006, and June 2006 and irrigated for 28 WAP every 1, 2, or 4 days with 3 L of water per irrigation event. Canopy GI and root extension to canopy spread ratio were determined at 28, 52, and 104 WAP. The entire canopy and roots were harvested 52 and 104 WAP to determine dry weight. In Expt. 1, wild coffee and orange jasmine plants irrigated every 2 days had greater GI than plants irrigated every 8 days at 28 WAP, but GI was not different at 52 or 104 WAP. Canopy dry weight at 52 WAP was greater for plants irrigated every 2 days than every 8 days, but there was no difference at 104 WAP. There was no difference in wild coffee or orange jasmine root dry weight or root extension to canopy spread ratio among the irrigation frequencies. In Expt. 2, there were no differences in GI, canopy dry weight, root dry weight, or root extension to canopy spread ratio of copperleaf or orange jasmine irrigated everyday compared with plants irrigated every 2 or 4 days. From the data collected in these studies, it appears that irrigating wild coffee or orange jasmine every 8 days during the first 28 WAP limited canopy growth but not root development. However, after 52 WAP, rainfall events appeared to be sufficient to eliminate any initial effects from irrigation frequency. Our data suggest that wild coffee, orange jasmine, and copperleaf from 3-gal containers can be successfully established in the landscape when irrigated with 3 L of water every 4 days for the first 28 WAP.