Evaluating Landscape Ornamentals for Un-Irrigated Landscapes in Western Oregon

Evaluating landscape ornamentals for un-irrigated landscapes in Western Oregon

Northwest Plant Evaluations is an Oregon State University Extension Service program which evaluates evergreen shrubs for use in un-irrigated landscapes in western Oregon. Evaluations are located at the OSU North Willamette Research and Extension Center in Aurora, OR. The goal of the program is to identify evergreen landscape shrubs which will thrive without any supplemental water in our summer- dry climate. Since 2000, the program has completed evaluations of Ceanothus, Cistus, Halimium and Grevillea. An evaluation of 75 accessions of manzanita (Arctostaphylos spp.) was planted in 2011 and is ongoing. Plants in the evaluations are collected as cuttings and are rooted and grown on before planting in the field. These are multi-year in-ground evaluations in which no special soil preparation is done and no water is supplied other than for establishment of the plants. In addition, plants are not fertilized, sprayed for pests or diseases, or pruned. Data on growth, flowering, cold hardiness and overall landscape appearance are collected over several years.

In each evaluation, some accessions have proven insufficiently cold hardy for landscape use, while others have shown no cold injury at all. In some cases, plants have succumbed to disease problems, either root-related or foliar. Insect pest issues have been very minor. The evaluations have also allowed observations of overall landscape aesthetic qualities over a number of years, which is helpful in that in some cases, especially with some Cistus and Halimium accessions, appearance declines significantly over 4-5 years after planting.

The program has identified a number of cold hardy accessions that would be effective in “low- maintenance” landscapes. A number of nurseries, both retail and wholesale, are growing selections from the evaluations in the Pacific Northwest and California. In addition, we have also assisted city personnel in Oregon with design of un-irrigated landscapes which include plants from our evaluations. The next evaluation, to be planted in 2018, will specifically focus on broadleaved evergreen groundcovers for un-irrigated landscapes.

Authors:

Neil Bell, Oregon State University Extension Service, 1320 Capitol Street NE, Suite 110, Salem, OR 97301. 503-373-3765. [email protected]

Heather Stoven, Oregon State University Extension Service, 2050 NE Lafayette Avenue, McMinnville, OR 97128. 503-434-8910.

Northwest Plant Evaluations webpage: http://horticulture.oregonstate.edu/content/northwest-plant-evaluation-program