Northwest Plant Evaluations

The goal of the Northwest Plant Evaluation program is to identify flowering shrubs suitable for use in landscapes of the Pacific Northwest, west of the Cascade Mountains. A priority of this program is to evaluate shrubs thought not to be particularly hardy in the region, but which offer compelling ornamental characteristics. The program is located at the Oregon State University North Willamette Research and Extension Center (NWREC) in Aurora, OR. Since 2000, the program has completed evaluations of Hebe (2000-2009), Ceanothus (2001-2005), Cistus (2004-2009) and Halimium (2004-2009). Evaluations of both Arctostaphylos and Grevillea were planted in 2009 at NWREC.

The initial criteria for the program, beginning with the Hebe evaluation in 2000, were to assess cold hardiness of as many cultivars or species of a given genus as could be acquired. The plants were rooted, grown on, then plantedout in the field and evaluated under ambient conditions. Hebe has a reputation for not being particularly cold-hardy, which in the case of some species and cultivars, is true. However, many of them are perfectly hardy in western parts of Oregon and Washington. Therefore the goal was to identify Hebe that could tolerate typical PNW winters without injury. Other data collected included growth, flowering, as well as overall landscape quality of the plants.

With subsequent evaluations, the data collected and other methodology have remained more or less the same. However, the main focus has shifted somewhat to evaluate genera known for drought tolerance. Starting with the Ceanothus evaluation in 2001, none of the plantings are irrigated after plant establishment, nor is any fertilizer applied or pruning done on the plants. While the Hebe evaluation (which was irrigated and fertilized) sought simply to identify hardy cultivars of the genus, the over-riding goal of all subsequent trials have been to develop fully drought-tolerant, hardy shrubs, especially groundcovers, for use in “low-input” Northwest landscapes.

Funding for the program has come from the following sources:

  • The Hardy Plant Society of Oregon
  • Agricultural Research Foundation
  • The Washington State Department of Agriculture (Nursery License Surcharge Program).

We are very grateful to our cooperators with this program, without whose help these evaluations would not be possible. Cooperating nurseries include:

  • Blooming Nursery (Blooming, OR)
  • Cistus Nursery (Portland, OR)
  • Dancing Oaks Nursery (Monmouth, OR)
  • ForestFarm (Williams, OR)
  • Joy Creek Nursery (Scappoose, OR)
  • Monrovia Nursery (Dayton, OR)
  • Xera Plants (Sherwood, OR)
  • Anderson Valley Nursery (Boonville, CA)
  • CalFlora (Fulton, CA)
  • Digging Dog Nursery (Albion, CA)
  • Native Sons Nursery (Arroyo Grande, CA)
  • Suncrest Nursery (Watsonville, CA)

Other Institutions which have supported the program include:

  • The Hebe Society (UK)
  • Lincoln Botanical (Christchurch, NZ)
  • University of British Columbia Botanical Garden (Vancouver, BC)
  • University of California Santa Cruz Arboretum
  • The Oregon Garden (Silverton, OR)
  • Strybing Arboretum (San Francisco, CA)
  • Rancho Santa Ana Botanic Garden (Claremont, CA)
  • Santa Barbara Botanic Garden
  • University of Washington Botanic Garden (Seattle, WA)

Other individuals and groups to whom we are very grateful include Mr. Robert G. Page (Leeds, U.K.) for his contribution of Cistus and Halimium to that evaluation. Thanks are also due to OSU Master Gardeners for assistance with plot maintenance and data collection.

Arctostaphylos (Manzanita) Evaluation in Western Oregon
Ceanothus Evaluation for Landscapes in Western Oregon
Evaluating Grevillea in Western Oregon
Hebe Landscape Evaluation
Rockrose (Cistus spp. and Halimium spp.) Evaluation for Western Oregon

For more information, please contact:

Neil Bell
Community Horticulturist, OSU Extension