Center for Urban Horticulture University of Washington Cooperative Extension Washington State University Vol. 6, No. 4 Autumn 1988 LANDSCAPE MAINTENANCE SEMINARS . . . for the landscape professional Cooperating: Center for Urban Horticul- ture, University of Washington; Cooper- ative Extension Service, Washington State University; Edmonds Community College; South Seattle Community College. • An Ecological Approach to Landscape Plant Selection Date : Wednesday, October 26 Time : 9 a. m. to 12 noon Location : Center for Urban Horticulture Improper plant selection results in poor per- formance and higher maintenance costs. The ecological approach emphasizes select- ing plants that tolerate the environmental stresses of a site and therefore require mini- mal maintenance. • “Principles of Ecological Plant Selection With an Emphasis on Climate,” Dr. Clem- ent Hamilton, assistant professor, Center for Urban Horticulture. • “Appropriate Plants for the Pacific North- west,” Timothy Hohn, curator of plant col- lections, Center for Urban Horticulture. • “Designing a Naturalistic Landscape,” Iain Robertson, assistant professor, Depart- ment of Landscape Architecture, University of Washington. PRO HORT Editorial Staff: Dr. John A. Wott George J. Pinyuh Van M. Bobbitt, editor Mites, Aphids, and Adelgids Date : Tuesday, November 15 Time : 9 a.m. to 12 noon Location : Center for Urban Horticulture Instructor : Dr. Art Antonelli These small pests account for a large nuiti- ber of problems of landscape plants. Symp- toms of their damage include yellowing leaves, malformed tissues, and galls. Learn about their biology, diagnosis, and control. Dr. Antonelli is an extension entomologist with Washington State University — Puyallup. He has written many extension bulletins and contributed to the Pacific Northwest Insect Control Handbook. This seminar qualifies for three hours of W.S.D.A. pesticide license recertification credit. A Systematic Approach to Diagnosing Plant Damage Date : Wednesday, December 7 Time : 9 a.m. to 12 noon Location : Center for Urban Horticulture Instructor : Dr. James L. Green Effective treatment of plant problems re- quires accurate diagnosis. The probability of correct diagnosis based on only one or two clues is low, but through this process of deduction and elimination the most proba- ble cause of damage can be determined. Dr. Green is an extension horticulturist, specializing in nursery and greenhouse crops, at Oregon State University. He also is editor of the Ornamentals Northwest news- letter. This seminar qualifies for three hours of W.S.D.A. pesticide license recertification credit. Parking Free parking will be available for those attending Pro Hort seminars. Please park in parking lot if space is available. OTHER EDUCATIONAL RESOURCES Tree Appraisal Workshop: The Basics. The Washington State Nursery and Land- scape Association and the Center for Urban Horticulture will sponsor an introductory tree appraisal workshop on Wednesday, November 9, 8:30 a.m. to 4:00 p.m., at the Washington Park Arboretum, Seattle. Through both classroom lecture and field practice, participants will learn the process used to determine tree values. Preregistra- tion is required. The fee is $45, including lunch and a copy of the International So- ciety of Arboriculture’s Valuation of Land- scape Trees, Shrubs, and Other Plants. For registration information call the Washington State Nursery and Landscape Association, (206) 863-4482. Horticulture Courses Offered at: • Edmonds Community College, 771-1679. • Lake Washington Vocational Technical Institute, 828-5627. • South Seattle Community College, 764-5336. Horticulture Library Open Monday Evenings. The Elisabeth C. Miller Library of the Center for Urban Horticulture will be open Mondays, 9:00 a.m. to 8:00 p.m., through December 19. Tuesday through Friday it is open from 9:00 a.m. to 5:00 p.m. (206) 543-8616. New Books at the Miller Library Clarke, D. L.; Bean, W. J. Trees and Shrubs Hardy in the British Isles: Supplement. London: J. Murray, 1988. 616 p. Decker, Henry F.; Decker, Jane M. Lawn Care: A Handbook for Professionals. Engle- wood Cliffs, NJ: Prentice Hall, 1988. 270 p. Greer, Harold E. Greer’s Guidebook to Available Rhododendrons. Rev. 2nd ed. Eugene, OR: Offshoot Publications, 1988. 185 p. Henderson, Carrol L. Landscaping for Wildlife. St. Paul: Minnesota Dept, of Natu- ral Resources, 1987. 144 p. Horn, David J. Ecological Approach to Pest Management. New York: Guilford Press, 1988. 285 p. Keim, Randolph; Humphrey, Wesley A. Diagnosing Ornamental Plant Diseases: An Illustrated Handbook. Publication no. 21446. Oakland: University of California, Div. of Agriculture and Natural Resources, 1988. 32 p. Mott, Lawrie; Snyder, Karen. Pesticide Alert: A Guide to Pesticides in Fruits and Vegetables. San Francisco: Sierra Club Books, 1987. 179 p. Rushforth, Keith D. The Hillier Book of Tree Planting and Management. Newton Abbot: David & Charles, 1987. 224 p. Smith, Miranda; Carr, Anna. Rodale’s Garden Insect, Disease & Weed Identifica- tion Guide. Emmaus, PA: Rodale Press, 1988. 328 p. ARTICLES Plant Palette: Oxydendrum arboreum Timothy Hohn Center for Urban Horticulture University of Washington With its acrid tasting leaves, Oxydendrum arboreum, or sourwood, is true to its scien- tific and common names. The scientific name is derived from the Greek oxy, mean- ing acid and dendron, meaning tree. Though sour to the taste, this native Ameri- can tree is sweet to the eye. A brief scan of the literature on trees of landscape and garden interest reveals a litany of superlatives concerning the aes- thetic character and garden worthiness of Oxydendrum arboreum. Trees at the Wash- ington Park Arboretum serve as adequate documentation — they are trouble-free and beautiful. Brian Mulligan, director emeritus, held them in high esteem for they are planted at several locations, in multiples of three, along the west side of Arboretum Drive. At this time of year, the sourwoods are one of our most colorful members of the collection. The sourwood belongs to that family which provides so many ornamental plants useful in the Pacific Northwest, the Ericaceae. This affiliation is most easily understood upon inspection of the flowers which are translu- cent white and urn-shaped like our native madrona, Arbutus menziesii. As handsome as the large, terminal panicles of flowers are, their appearance among the withering greens of August is an additional bonus. But the attraction doesn’t stop there. Often amidst this floral draperie, the lustrous green leaves begin to reflect the late sum- mer sunsets with mottled colors of orange, scarlet, and plum. Spring is the third season of interest as the bronzy green, shiny new leaves of Oxydendrum unfold. The sour- wood is naked and subdued in the winter, resting up for its eight month display with only its slender silhouette and furrowed bark for ornament. Among the members of the heath family, Oxydendrum arboreum is most closely al- lied to Pieris. As a slender-crowned tree, the largest specimens are found on the western flanks of the Great Smokey Mountains in Tennessee where specimens may reach 80' in height. Trees at the Arboretum are up- wards of 35' -40' after 40 years. The leaves are decidious, alternate, lanceolate to about 8" long and minutely toothed. The flowers are borne on a lax panicle that can be as much as 10" long at the terminal end of the branches. The bark is similar to sassafras in that it is thick and deeply furrowed, occa- sionally cross-checked to give it a blocky appearance. Sourwood ranges from the Smokeys up the Appalachian Mountains to Pennsylvania and eastward to the coastal plain. It is most often found on well drained slopes close to streams and drainage areas in broken oak/hickory or oak/pine woods. I have seen them as single specimens scat- tered among the larger trees. Our experiences in the Arboretum indicate that Oxydendrum arboreum is a forgiving and undemanding landscape specimen. It does best with conditions suitable for other ericads with the exception of a bit more sun. An ideal exposure would be full to partial sun with shaded roots or a fully exposed position with southern protection. Flower- ing and foliage color are best with sunshine. Plants in the Arboretum — 40 year old plants with limited exposure to the sun — are relatively drought tolerant although summer irrigation will speed what is a rather slow growing tree. Even though it is adapta- ble, sourwood is not a recommended tree for industrial or polluted areas. The seeds will germinate without pretreatment if sur- face sown on milled sphagnum and ver- miculite and subjected to mist. Cuttings are a less preferable method of propagation but are successful if taken in July as soft side shoots containing a heel and treated with 90 ppm IBA soak. The sourwood was first introduced into cul- tivation in 1747 and is probably best known in the Southeast for the quality it lends to honey. We could certainly reap the benefits of its tasty honey here in the Northwest for it is perfectly hardy west of the Cascades. Its many ornamental features dictate the use of Oxydendrum as a specimen tree. The nar- row crown and medium to short stature make it perfectly suitable for small urban landscapes. Although it is slow growing, the ornamental features of the sourwood are expressed early in life. These trees make a fine grove of 3-5 specimens, especially when accompanied by a background of fine-textured evergreens. Single specimens also are useful for toning down abrupt cor- ners and leaning over patios. Rediscovering a Native American: Mountain Laurel9 Kalmia latifolia L.9 is Increasing in Popularity Dr. Rita L. Hummel Puyallup Research and Extension Center Washington State University Kalmia is a truly American genus containing seven species native from Alaska to Cuba. A member of the Ericaceae or heath family, Kalmia is related to such notables of the plant world as the rhododendrons, azaleas, blueberries, and cranberries. The species of primary importance as an ornamental, Kalmia latifolia, mountain laurel, is native to the eastern United States and was first used by the early colonists in their gardens. Mountain laurel is a broad-leaved evergreen shrub or small tree with a spreading habit that seldom grows taller than 12 feet. The showy flowers resembling inverted um- brellas are borne in clusters in late spring and early summer. Mountain laurel flowers have a unique method of pollen distribu- tion. All ten anthers are held under tension in pouches on the open flower and when an insect alights to collect nectar it triggers the anthers to spring forward discharging their pollen. The underside of the insect is smeared with pollen which is carried to a new flower, dusting the stigma and com- pleting the process of cross pollination. Growing mountain laurel can be a chal- lenge for the experienced gardener. Its growth requirements are similar to those of rhododendrons and azaleas. Well drained, acid soils with good aeration are a key to success with mountain laurel. Hardy to USDA zone 5 with winter minimum tem- peratures down to - 29°C ( - 20°F), moun- tain laurel should be cold hardy throughout most of Washington. However, some pro- tection is needed from winter desiccation caused by drying winter winds and bright sun. Only within the past three decades has the beauty of mountain laurel begun to be re- discovered by the gardening public. Moun- tain laurel’s increased popularity can be credited to the breeding and selection of new cultivars. These cultivars have flower colors ranging from white to nearly pure red in assorted banding patterns, and exhibit a variety of leaf forms and plant growth hab- its. Propagation research has made possible the rapid multiplication of the new cultivars by using micropropagation (tissue culture) techniques, and educational efforts have led to a heightened level of awareness of mountain laurel, possibly our loveliest native American flowering shrub. For addi- tional information on mountain laurel, the reader is referred to Kalmia: The Laurel Book II (1988, Timber press, 9999 SW Wilshire, Portland, OR 97225) by Richard Jaynes, breeder, nursery grower, and inter- national Kalmia authority. With many new cultivars to choose from and the know how to propagate them, it would seem that the difficulties for moun- tain laurel growers are solved. Unfor- tunately this is not true. There is little defi- nite information to guide the nursery grower producing mountain laurel in con- tainers and problems abound. Information is also needed to insure the successful trans- planting and establishment of mountain laurel in the landscape. Research underway at Washington State University-Puyallup is aimed at solving some of the remaining problems in mountain laurel culture. Nur- sery production experiments will determine an optimal container-growing-medium and fertilizer regime for producing high quality roots and tops on an assortment of moun- tain laurel cultivars. Results of our 1987 study indicate a 4 fir bark: 1 peat moss me- dium could be successfully used to produce one gallon container plants. In 1988, ex- periments are being conducted to test the effect of an all fir bark medium and several fertilizer treatments on root and shoot growth. Procedures for transplanting and growing mountain laurel in the landscape are also being evaluated. In the spring of 1988, three mountain laurel cultivars were transplanted from one-gallon containers into a full sun field location at Puyallup. The backfill around the root system was either amended with 50% peat moss or no amendment was added. Growth and quality of the plants will be recorded, and the results will be communicated in future editions of Pro Hort. Water in the Urban Landscape: Hydrologic Budgeting Dr. Deane Wang Center for Urban Horticulture University of Washington Understanding water in the urban land- scape is difficult. Where does it come from? Where does it go? How does it alter the urban environment? Beyond saying that the water comes from rain and pipes and runs down creeks and drains, we have not accurately described the moisture condi- tions over the varied urban landscape. Given this lack of data, how can we effec- tively manage this increasingly precious re- source? A useful framework for approach- ing the problem uses something called a “hydrologic budgeting scheme.” The basic idea behind this approach is that water is never destroyed — it merely changes forms or slips out of sight. To use the hydrologic budgeting scheme, one draws a conceptual “box” around the ecosystem in question and then attempts to balance the water budget for that system. The ecosystem in question can vary considerably in size, from the backyard, to the block, to the city, to the county, all the way to the state/regional level. To apply the water budget (also known as the hydrologic cycle) concept to a small piece of vegetated landscape, we must identify (1) the inputs and outputs of water and (2) the water in storage. Precipitation and irrigation water are the important in- puts for an urban landscape; that water is stored primarily in the soil; and outputs from the landscape include drainage, evap- oration from wet surfaces, and transpiration by plants. Most of the urban landscape is not a wet- land, so additional water, rather than less, is usually required. We have four options for increasing the supply of water for landscape plants: (1) increasing inputs (usually by irri- gating) to replenish storage, (2) increasing storage, (3) reducing runoff and drainage loss, and (4) increasing water-use efficiency. Option #1, increasing inputs, is not an op- timal solution in an area where rapid popu- lation growth both increases the demand for water and reduces the land base from which to draw water. Option #2, increasing storage, can be achieved in two ways: (1) by increasing the soil’s water-holding capacity and (2) by en- couraging more extensive root systems, thus increasing the volume of soil from which water can be drawn. Soil con- ditioning can help in both instances. The Registration Form l Landscape Maintenance Seminars Complete Series: Plant Selection, Mites, Diagnosis $31.50 Ecological Plant Selection $13.00 Mites, Aphids, Adelgids $13.00 Diagnosing Plant Damage $13.00 TOTAL: $ Group Rates: Firms/institutions sending two or more employees per seminar. The rates are: 2-5 employees $10.50/person 6 or more employees $ 9.50/person To qualify for group rates: ( 1 ) firm’s registration must be received at least one week in advance; (2) all registrants must be from the same firm; and (3) total registration fee must be paid with one check or purchase order. Firms using purchase orders must make prior registration arrangements. Make checks payable to the University of Washington; no bank cards. Portion of fees may cover refreshments and speakers’ expenses. Receipts will not be returned by mail; they will be available at the door. NAME ADDRESS CITY STATE ZIP PHONE (DAY) PHONE (EVE) Mail payment and registration to: Urban Horticulture Program, University of Washington, GF-15, Seattle, WA 98195 For more information please call 545-8033. addition of organic matter can increase the water-holding capacity of both sandy and compacted soils. Conditioning also can im- prove soil aeration which allows for a more extensive rooting pattern. Option #3, reducing runoff and drainage loss, can be accomplished by detaining the water on site for a longer time and thus increasing the infiltration of water into the soil. Water bars, twisting drainage paths, contouring of swales, and temporary ponds can increase the time a drop of rain spends on a landscape before it rushes off to a storm drain or creek. Here again, soil con- ditioning can help by loosening compacted soils and increasing the infiltration rate of water. Option #4, increasing water-use efficiency, can be realized in large part through appro- priate plant selection. Plant form and leaf morphology can greatly alter the rate at which water is lost from a plant (e.g., cactus vs. lettuce). Some plants go dormant during dry spells; others store carbon dioxide by night so they will not lose water by day in photosynthesis. As an ecosystem, the water-use efficiency of a landscape can be increased by reducing evaporation from the soil. Both the shade provided by living plants and the protection provided by a mulch of organic litter can CENTER FOR URBAN HORTICULTURE University of Washington, GF-15 Seattle, WA 98195 reduce direct evaporation from the soil. The water budget approach is useful tool to analyze how a landscape might be better designed and managed to conserve water, but more research is needed. Our current knowledge of which plants to use in any given hydrologic situation is quite poor; the use of plants in community groups is not well understood; and, over the expanse of a city, we know very little about how water is distributed. New tools are being developed to permit a better understanding of the urban water sit- uation. Current research efforts at the Cen- ter for Urban Horticulture are aimed at quantifying soil water conditions through- out the city and at finding “new” plants which are adapted to our winter-rain/ summer-drought climate. How Dry Are Our Summers? George Pinyuh Cooperative Extension Washington State University For folks who don’t believe in the droughtiness of ordinary western Washing- ton summers, a comparison of Seattle-Ta- coma summer rainfall with a few other areas of the world might prove interesting. These areas, by the way, are where a large major- ity of the ornamental plants we use orig- inally came from. Obviously, they evolved in locales where summer rainfall is not only the norm, but in most cases the amounts they receive are extraordinary. The rhodo- dendrons, azaleas, magnolias, dogwoods, maples, and turfgrasses that come from such areas will either require a considerable amount of irrigation or will need to be man- aged appropriately with water conserving techniques in mind. The average rainfall for the four months of May through August in the Seattle-Tacoma area is 5.1 inches. For the same period, New York City’s precipitation is 20.8 inches, about four times greater. During this period in the Himalayas and western China an astonishing total of 42.8 inches comes down! Japan, another source of many of our ornamentals, goes into the record books with 23.6 inches of precipitation dur- ing the summer months. In other words, when plants’ demand for water is the great- est, even in a normal summer they can count on precious little falling from the sky in our area. Average Rainfall: May— August Himalayas, w. China 42.8 in. Japan 23.6 in. New York City 20.8 in. Seattle-Tacoma 5.1 in. Nonprofit Org. U.S. Postage Paid Permit No. 62 Seattle, WA AUTUMN 1988