Evaluating the Water Use and Climate Zone Tolerance of Ornamental Plants for Sustainable Landscapes

Urban water availability is of primary concern to the summer-dry Western U.S.  Unstable supplies have become more uncertain due to increasingly drier winters, and chemical laden runoff from over-watered landscapes threatens the health of waters that receive urban runoff.  This has led to regulations on landscape planning and water use.  To address these restrictions and concerns, landscapes are being installed or redesigned with water conserving plants, and designers and growers are seeking new plant introductions for this sustainable landscape trend.   Despite the obvious advantage of having information on plant water use for Mediterranean climates, there is very little research-based data for landscape species. To address these issues, irrigation and climate zone trials were begun in 2005 on landscape perennials considered by the UC Davis Arboretum to be water conserving, pest tolerant, and disease resistant.  Ten species were evaluated in full sun field plantings on 4 levels of irrigation based on reference evapotranspiration (ET₀), the amount of water loss from a reference crop.  This experimental design was replicated with 9 shade-loving species under a 50% shade structure.  Six replicates of each species and treatment were planted and established on regular irrigation the first year. The following May through October they received an irrigation treatment at 20, 40, 60, or 80% of ET₀.  Monthly measurements and qualitative evaluations were made to assess differences between treatments.  Many of the same plants were also placed in demonstration gardens in different climate zones across California where UC Master Gardeners evaluated the performance of the plants.  In many cases, there were no significant differences between treatments in either plant growth or quality, while a few species showed differences in one or both areas.  The plant water use data being generated in these trials is needed to support the necessary transition to sustainable gardens and irrigation strategies in summer-dry Mediterranean climates.

Abstracts:

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