We evaluate shrubs for drought tolerance, cold hardiness and overall suitability for western Oregon landscapes. The overall goal is to provide drought-tolerant, low maintenance flowering shrubs for gardeners, nurseries and landscapers west of the Cascade Mountains. Between 2000 and 2019, we completed landscape evaluations of Ceanothus, Cistus, Halimium, Grevillea and Arctostaphylos. We are currently evaluating 80 taxa of broadleaved evergreen groundcovers which are planted at the Oregon State University North Willamette Research and Extension Center (NWREC) in Aurora, OR.
The climate in the Willamette Valley is temperate Mediterranean, with summers that are distinctly warm and dry from June through October. Winters are cool and wet, with rainfall averaging 35 inches. The majority of the valley is USDA Hardiness Zone 8. The main challenges to non-native plants is the occasional severe winter cold snap and the lengthy summer drought. To grow plants in low-maintenance landscapes where irrigation is not provided, then the plants have to be both cold hardy and tolerant of summer heat and drought. Our plant evaluations are multi-year, in-ground landscape evaluations where the plants receive no summer irrigation, fertilizer, pruning, pesticide applications or other care. The plants are evaluated over 4-5 years for growth, cold hardiness, flowering, pest and disease problems and overall appearance. Each evaluation has identified individual cultivars which exhibit tolerance of environmental stresses and would look good in area landscapes.
The evaluations previously done on various plant genera identified some cultivars that performed well as lower-growing evergreen plants that would make good groundcovers. Groundcovers are the workhorses of low-maintenance landscapes, providing aesthetic appeal as well as providing weed control. The current evaluation at NWREC was planted in 2019 and consists of 80 different evergreen shrubs of various sizes which could be utilized as groundcover. The goal is to identify an array of shrubs that could be used for groundcover in low-maintenance landscapes.