Growth, Flowering, and Cold Hardiness of Rockrose in Western Oregon

Ninety-three species, cultivars, and hybrid selections of rockrose (Cistus spp., Halimium spp., and xHalimiocistus spp.) were evaluated for growth, flowering, and cold hardiness in a landscape trial in Aurora, OR, from 2004 to 2009. Plants were irrigated to aid establishment when planted in summer 2004, but thereafter were not watered, fertilized, or pruned throughout the trial. Cold damage was recorded following freezing events in Feb. 2006 and Dec. 2008 in which low temperatures were 20 and 17 F, respectively. Those plants that consistently suffered the most cold damage were Halimium atriplictfolium, Cistus creticus ssp. creticus 'Tania Compton', Cistus xpauranthus, and Cistus albidus forma albus. Other plants showed cold damage related to poor vigor. The length of the flowering period and foliage quality varied widely among plants in the evaluation. The plants with the longest flowering period were Halimium xpauanum, Cistus inflatus, Cistus xpulverulentus 'Sunset', and xHalimiocistus 'Ingwersenii', all of which flowered for more than 55 days. Plant form and foliage quality declined drastically for some plants during the evaluation. Those that retained the best foliage quality included Cistus xobtustfolius, Cistus xlaxus, Cistus salviifolius 'Gold Star', Cistus 'Gordon Cooper', Halimium lasianthum 'Sandling', Halimium 'Susan', and xHalimiocistus sahucii. Based on ratings of foliage and bloom time, as well as hardiness, several Cistus are recommended as drought-tolerant groundcovers, including Cistus xgardianus and C. xobtusifolius. Cistus xlaxus, C. inflatus, Cistus 'Gordon Cooper', Cistus 'Ruby Cluster', and Cistus 'Snow Fire' are suggested as tall groundcovers or landscape specimens. Several Halimium are recommended for landscape use, including H. lasianthum 'Sandling', Halimium 'Susan', H. xpauanum, and xHalimiocistus 'Ingwersenii'.