As climate change transforms the weather in Western Oregon, more and more nursery owners, landscapers and home gardeners are looking for plants that are fully drought-tolerant and cold-hardy. Development of genuinely low-input landscapes will expand the plant palette that can be grown by Oregon’s nursery and greenhouse industry, which remains the leading agricultural commodity in the state, with a value of $1.22 billion in 2022.
Oregon State University Extension Service and the OSU Agricultural Experiment Station both have a long history of assisting the state’s nursery industry. Neil Bell, an Extension community horticulturist, determined he would help again by running plants through an extensive testing process at the OSU North Willamette Research and Extension Center (NWREC) in Aurora and the Oregon Garden in Silverton.
Local evaluations provide data on plant adaptability to this region and provide nurseries with access to plants for propagation.
The original goal of these evaluations was to research the hardiness of Hebe, a genus of flowering shrubs native to New Zealand that are very popular and showy, but in many cases lack sufficient cold hardiness for landscape use in Western Oregon. The overriding goal of all subsequent trials has been to develop fully drought-tolerant, hardy shrubs, especially groundcovers, for use in "low-input" Pacific Northwest landscapes. Local evaluations of drought-tolerant, evergreen groundcovers would provide gardeners and landscapers with data on plant adaptability to this region and provide nurseries with access to plants for propagation.
“Development of genuinely low-input landscapes for Western Oregon will require use of drought-tolerant, evergreen ground covers, few of which are currently used in local landscapes because data on their adaptability to local conditions are not available,” Bell said. “As a result, landscapers tend not to request these plants and nurseries do not grow them in the absence of this data.”
Instead, he said, better known but poorly adapted species are used here that tend not to thrive without significant outputs of water, fertilizer, pesticides and labor. Local evaluations provide data on plant adaptability to this region and provide nurseries with access to plants for propagation.
In addition to Hebe, Bell has evaluated Cistus, Halimium, Ceanothus, Grevillea and Manzanita to determine plant growth, hardiness and overall quality. In each case, cooperators, both domestic and international, provided plant material that was propagated, grown and planted at NWREC. Data on each plant group was acquired over several years and includes plant size, flowering and overall landscape worthiness, as well as cold hardiness ratings.
An evaluation of broadleaved evergreen ground covers was undertaken in 2017, including an expedition to France to collect drought-tolerant plants in Meze. The initial planting in this evaluation took place at NWREC in September 2019, and featured 80 different ground covers, differing widely in size as well as all ornamental characteristics.
Another evaluation of ground cover plants started in 2018, that includes new accessions of Phlomis and Cistus collected at the Plant Heritage collections of those genera the United Kingdom. That planting at NWREC took place in November 2021 and includes 21 taxa of Phlomis, among a total of 51 taxa total planted in this part of the evaluation.
All information on the trials is available on the Northwest Plant Evaluations website. Results have been shared with nursery industry publications like Digger, the magazine of the Oregon Association of Nurseries; Nursery Management and Production; and Pacific Horticulture. In 2024, Bell and colleague Heather Stoven published the series "Top 5 plants for unirrigated landscapes in Western Oregon."