2014 ASHS Annual Conference

Irrigation Best Management Practices for container plant production indicate that plant species should be grouped according to water needs.  Current recommended grouping is primarily based on opinions from producers. Objective comparisons in water usage between species are often confounded by variable plant sizes and container spacings that existed during measurements.  The objective of this research was to compare ET rates of plant species with containers spaced to achieve full canopy coverage.

We evaluated uniform and marketable-sized plants grown in trade #3 (approximately 10-L) containers filled with pine bark-based substrates at nurseries in Florida and Virginia.  The plant species tested included Ilex cornuta 'Burfordii Nana', Loropetalum chinense var. rubrum 'Burgundy', Podocarpus macrophyllus, Rhaphiolepis indica 'Alba', Rhododendron spp. 'Conversation Piece', Rosa spp.  Sunrosa® Pink, and Viburnum odoratissimum in Florida and Berberis thunbergii f. atropurpurea 'Rose Glow', Gardenia jasminoides 'Frostproof', Hydrangea paniculata Pinkie Winky™, Rhododendron spp. 'Girard’s Crimson', Spiraea japonica 'Tracy' (Double Play® Big Bang), and Weigela florida Wine & Roses® in Virginia.  Nineteen plants of each species were arranged in an offset pattern (hexagonal) and spaced to achieve full canopy coverage of the production area.  Seven interior plants were weighed after irrigation and again 24 hours later.  ET (cm) on an area basis was calculated as the difference between the wet and dry weights (cm³) divided by the area allotted each container (cm²).

In Florida, ET ranged from 0.77 cm for Podocarpus to 1.22 cm for Viburnum and ET of Viburnum greatly exceeded the ET of the other six species.  In Virginia, ET ranged from 0.74 cm for Rhododendron to 1.15 cm for Berberis and ET of Berberis greatly exceeded the ET of the other five species.  Excluding Berberis and Viburnum, differences in ET of 0.16 and 0.31 cm were determined for species tested in Virginia and Florida, respectively.  These differences are probably not significant considering the overhead sprinkler distribution uniformity and a common daily application rate of 0.8-1.0 cm.