This article is part of a publication series based on the Northwest Plant Evaluation Program at Oregon State University. This research program has evaluated flowering shrubs for their suitability in landscapes in western Oregon since 2000. These publications highlight plants that were successfully grown without irrigation in the trials as well as techniques for growing and establishing drought-tolerant plants in the landscape.
The research trial evaluating Grevillea or ‘spider flowers’ occurred from 2011 to 2014 at OSU’s North Willamette Research and Extension Center in Aurora, Oregon. The trial compared 57 accessions of spider flower, which were irrigated only during establishment in the fall of 2011, and were not pruned or fertilized. Information collected about the plants included bloom time, size, and cold hardiness. We have selected the top 5 performing plants for western Oregon landscapes based on our research and describe them below.
Overview of Grevillea
Grevillea, known commonly as ‘spider flowers,’ is a genus of 360 species of woody evergreen shrubs or trees, primarily native to Australia. This genus is native to regions that are mild in temperature, with hot, dry summers and moderate, rainy winters. The size and growth habit of Grevillea shrubs vary widely in habit and can be prostrate and wide-spreading to tree-form.
Grevillea gets its common name ‘spider flowers’ from its unusual flowers, which are long and slender and borne in clusters. Flower color is typically in shades of yellow, red or white. Most Grevillea flowers have a long bloom period, often blooming in winter, into spring and beyond. The nectar of the flowers is also irresistible to hummingbirds as well as bumblebees and honey bees.
Leaves of Grevillea can be quite diverse, from small needle-like leaves to feathery dissected leaves which can be green to grey in color. The leaves of those hardiest in our region, however, are often simple to needle-like and green.
These shrubs are best grown in full sun and are well-adapted to summer drought. The roots of Grevillea are particularly well adapted at extracting scarce nutrients, being native to areas with poorer soils. Therefore, members of this plant species thrive on well-drained soils with average to poor fertility. Grevillea are very sensitive to rich soils and phosphorus fertilizers. In compacted soils, an initial amendment of compost, or double digging within the landscape bed prior to planting, is all that is needed for soil preparation. After planting, avoid the use of any phosphorus-containing fertilizers or additional compost applications.
Most Grevillea are grown in USDA Hardiness Zone 9 or higher, as many are sensitive to cold temperatures. However, we have been able to evaluate some selections that survive well in western Oregon in Zone 8. If you are in a colder microclimate, planting these on a southern exposure in a sheltered area may be beneficial.
They also perform well as container plants which can be moved to a protected location in the event of a cold snap. The open flowers of these winter-blooming shrubs can be damaged during severe cold spells; however, unopened flowers are protected and the plant will continue blooming as temperatures rebound.
