Evaluating manzanitas (Arctostaphylos spp.) for western Oregon landscapes
Arctostaphylos is a genus of woody, evergreen shrubs or small trees native primarily to western North America, from southern British Columbia into Mexico. One species, A. uva-ursi, as well as the closely related Arctous alpinus and Arctous ruber, are collectively referred to as bearberries and are found in circumpolar areas of North America, Europe and Asia. The various species are found in a wide range of habitats, from coastal areas, to chaparral and mountainous regions. 
The common name of most species is manzanita, Spanish for “little apple”, which refers to the small rounded fruit, which is often green or in various shades of red.
Because of the wide geographic distribution, the habit of manzanitas varies widely from prostrate, wide-spreading groundcovers to rounded shrubs to small trees.
The larger-growing plants often have intricately twisted branches, a structure which may be enhanced by a beautiful, polished mahogany-like bark.
Although the leaves on all manzanitas are simple, the color and texture varies considerably from the small glossy green leaves of A. uva-ursi, to the large, vertically-orientated leaves of many species from hot climates. Leaf color is often glossy green, but some species and cultivars feature hairy and/or waxy leaves which take on a blue or silvery appearance. 
In some cases, the new foliage takes on reddish tints which add to the ornamental appeal of the leaves.
Flowers typically appear in late winter or earliest spring and are shades of white or pink.
The flowers provide a source of forage for bumblebees during the early part of the growing season.
The best known of the Arctostaphylos, and the most widely grown by far, is A. uva-ursi, popularly known as bearberry or kinnikinnick. This species has a circumpolar distribution and typically forms a ground-hugging evergreen mat.
Several forms have been selected and introduced to cultivation, and in Oregon and Washington these are widely utilized as groundcovers, sometimes in situations where considerable drought tolerance is required. Unfortunately, kinnikinnick is not always a very vigorous or successful groundcover, as it often suffers, particularly west of the Cascades, with disease and pest problems.
This species is also very low-growing, and as a result may not suppress weeds as effectively as a taller groundcover. In addition, the most commonly grown form, A. uva-ursi ‘Massachusetts’, originated from a population in the northeastern U.S. and is not adapted, as western species and selections are, to summer drought. Other selections of this species such as ‘San Bruno Mountain’ perhaps offer better disease and drought tolerance but have not been generally available.
Beyond A. uva-ursi, none of the many other manzanitas are used to any extent in western Oregon landscapes except by enthusiasts. This even includes the manzanitas native to Oregon, of which there are quite a number (see the Oregon plant atlas at the Oregon Flora Project website: http://www.oregonflora.org/). A large number of species are native however, to dry regions of the western U.S, although they have not been utilized in Pacific Northwest landscapes. Many of these are used successfully as groundcovers in California in landscapes where drought tolerance is required. These include A. edmundsii, A. hookeri and A. nummularia, as well as a number of selections or hybrids, including ‘John Dourley’, ‘Pacific Mist’ and ‘Emerald Carpet’. These are either not currently utilized in the Pacific Northwest, or used very rarely. Taller shrub species such as A. densiflora, A. manzanita and A. pajaroensis are similarly unused, even though they could form valuable components of genuinely drought-tolerant landscapes.
The reason why these plants are not used is because a near-complete lack of information about their growth, hardiness, pest resistance or other landscape characteristics in the PNW. As a result none are generally available in the wholesale trades, even though they may have been grown on a limited basis successfully by enthusiasts and retail nurseries.
To help to address this situation, an evaluation of these plants was begun at the OSU North Willamette Research and Extension Center in Aurora, OR in September 2009. Eighty-five cultivar and species selections were planted out in a 1-acre plot for a multi-year evaluation.
Much like the other evaluations that have been conducted, this one will measure plant growth, as well as documenting flowering times, pest and disease problems and cold hardiness.
References
A definitive work on the taxonomy of manzanitas is not currently available, however, information on individual species and cultivars and their culture can be sourced from a variety of book and web resources, some of which are listed below.
Books:
Plants of western Oregon, Washington and British Columbia. 2005. Eugene Kozloff. Timber Press.
The Jepson Manual: higher plants of California. 1993. James C. Hickman (ed.). University of California Press.
Gardening with native plants of the Pacific Northwest (2nd ed.). 1997. Arthur Krukeberg. University of Washington Press.
Native Treasures. Gardening with the plants of California. 2006. M. Nevin Smith. University of California Press.
Complete Garden Guide to the Native Shrubs of California. 1994. Glenn Keator. Chronicle Books.
California native plants for the garden. 2005. Carol Bornstein, David Fross and Bart O’Brien. Cachuma Press.
The Sunset Western Garden Book, 8th ed. 2007. Oxmoor House.
Websites
The Oregon Plant Atlas of the Oregon Flora Project: http://www.oregonflora.org/
Natural Resources Conservation Service Plants Database: http://plants.usda.gov/index.html
USDA-ARS Germplasm Resources Information Network: http://www.ars-grin.gov/
CalFlora: http://www.calflora.org/
E-Flora BC: http://www.geog.ubc.ca/biodiversity/eflora/
Website creator:
Neil Bell
Community Horticulturist
OSU Extension Service
Marion and Polk Counties
3180 Center Street NE #1361
Salem, OR 97301
503-361-2671
neil.bell@oregonstate.edu