The 2009 ASHS Annual Conference

Ninety-three species, cultivars, and hybrid selections of Cistus spp., Halimium spp. and × Halimiocistus were evaluated for growth, flowering, landscape quality, and cold hardiness in Aurora, OR, from 2004-07. The evaluation site was a south-sloping 0.2 ha plot in full sun at the OSU North Willamette Research and Extension Center.  Plants were spaced 1.5 m apart within rows and rows were spaced 3 m apart in a randomized, replicated design.  Plants were watered by hand at planting in May 2004 and received periodic overhead irrigation through Aug. 2004, after which no irrigation was applied for the duration of the study.  Plants were not fertilized or pruned during the evaluation.  With the exception of ‘Enigma’, all plants of which died in 2004, all cultivars grew well through 2007. Growth habit varied greatly among the cultivars, from low, spreading plants such as Halimium calycinum and Cistus creticus ‘Lasithi’ to taller, rounded shrubs like C. ‘Snow Fire’ or C. ‘Ann Baker’ and upright shrubs like C. x aguilarii and C. x verguinii. Flowering commenced in mid-April with H. calycinum and H. umbellatum, but the majority of cultivars flowered from early May through mid-June, and a few cultivars continued to flower well into July.  The length of the flowering period varied significantly from several days to several weeks. Striking differences in plant quality became apparent as plants matured. Some cultivars, such as Gordon Cooper and Snow Fire, retained good foliage quality and plant habit, while other cultivars such as Victor Reiter and Silver Pink declined in appearance and became sparsely foliated. Cold injury was generally moderate during the evaluation period, with most damage being limited to foliage or modest stem dieback. The plants showing the most cold damage were Cistus creticus ‘Tania Compton’, C. x pauranthus and Halimium atriplicifolium. Several cultivars are suggested for landscape use as dwarf groundcovers including C. ‘Grayswood Pink’, C. x gardianus, and H. lasianthum. More vigorous plants that function effectively as taller groundcovers include C. x laxus and C. x obtusifolius.