0, Center for Urban Horticulture University of Washington Vol. 8, No. 1 Cooperative Extension Washington State University Winter, 1990 LANDSCAPE MAINTENANCE SEMINARS ... for the landscape professional Cooperating: Center for Urban Horticul- ture, University of Washington; Coopera- tive Extension Service, Washington State University; Edmonds Community College; South Seattle Community College. Urban Trees: Construction Impacts Robin Morgan, Urban Forester Thursday, January 25, 1990 9:00 am to Noon; $13 Center for Urban Horticulture Before a street tree is planted, site selection and events related to road construction will determine the environment in which the tree will grow. Such things as water, air, and nutrient availability will be impacted by construction. Understanding the planning and logistics of construction projects will help the horticulturist to develop successful strategies for planting and managing trees. Robin Morgan is Urban Forester for the County of Sarasota, FL, and author of Trees for Eugene and An Introductory Guide to Community and Urban Forestry in Washington, Oregon, and California. She will illustrate relevant construction practices and their impacts on tree health and lead a discussion panel which includes members from municipal planning, con- struction, utility, and arboricultural areas. ProHort editorial staff Dr. John A. Wott George J. Pinyuh Eric Nelson WSNLA/CUH Plant Management at the Retail Level Wednesday, February 28, 1990 9:00 am to 4:00 pm; $35 Center for Urban Horticulture Presented in co-operation with the Wash- ington State Nursery and Landscape Asso- ciation, this day-long program examines issues of plant management in the retail setting. Practical information will be provided on watering, using soil mixes, fertilizing, win- terization, pests and diseases, handling balled and burlapped plants, and more. Emphasis will be given to information which can be passed-on to the retail customer to help them to be successful after the sale. This program qualifies for three hours WSDA pesticide license recer- tification credit. To request registra- tion forms, call 1-800-672-7711 (WSNLA), before February 14, 1990. Annuals: New Approaches Tuesday, March 20, 1990 6:30 to 9:30 pm; $13 Center for Urban Horticulture What’s new in annual plants? Marianna Metke, of Skagit Gardens, shows plant selections for color, foliage effects, and extending the season. Special topics in maintenance Keith Degler, of Evergreen Services Corp., illustrates comon maintenance problems and discusses their solution. Innovative container plantings Peggy Campbell, of Molbak's Nursery, illus- trates new ideas for the design of container plantings with annuals. Other Educational Resources South Seattle Community College Horticulture Courses, Winter, 1990. Weekdays: Greenhouse Operations, Win- ter Plant Identification, Plant Propagation, Drafting, Landscape Design/Construction, Contracts & Specifications, Plant Diseases. Evening classes: Pruning, Small Engine Repair, Irrigation Systems. 764-5336. Edmonds Community College Horticulture Courses, Winter, 1990. Weekdays: Winter Plant Identification, Soils, Pesticide Laws and Safety, Pruning, Propa- gation, Landscape Design, Sprinkler De- sign, Landscape Renovation, Job Training, Greenhouse, Early Rhododendrons. Satur- days: Pruning. Evenings: Plant Plant Identi- fication, Grafting, Wholesale Nursery Op- erations, Retail Nursery Operations, Land- scape Materials. 771-1608. Lake Washington Voc-Tech Horticulture Courses, Winter, 1990. Weekdays: Environmental Horticulture, Flo- ral Design/Flower Shop Assistant. Evenings (short courses): Floral Design, Pruning, Turf Management, Nursery Business Manage- ment, Residential Lawn Care, Propa- gation, Greenhouse. 828-5627. Pesticide licensing credit. An evening class entitled “Lawn Renova- tion,” offered through the Center for Urban Horticulture continuing education program, carries two hours of WSDA pesticide license recertification credit. Ciscoe Morris, grounds supervisor at Seattle University, will teach the class, to be held on Thursday, March 15. Preregis- tration is required. For registration infor- mation, call 545-8033. Registration information See Page 3 Root Facts — A Review Van M. Bobbitt Cooperative Extension Service Insufficient understanding of the root sys- tems of trees has led to the development of management practices which are ineffec- tive or even detrimental to tree health. By understanding and applying research-based information developed over the past dec- ade, landscape managers can modify their cultural practices to the benefit of trees. Horizontal Root Spread Tree roots spread much farther than once thought, usually growing well beyond the dripline (branch spread). Studies have shown root spreads ranging from 1.68 times the dripline radius for Fraxinus pennsyluanica to 3.77 times for Magnolia grandiflora. This has led to revised recommendations for the application of fertilizers and herbicides around trees. Fertilizers should be applied not only within, but also beyond the dri- pline. Potentially harmful herbicides once carried instructions that they not be applied within the dripline of trees; it is now clear that this is not an adequate margin of safety. Root Depth Deep root systems are uncommon in shade trees, and most of the absorbing roots are in the top few inches of soil. Urban trees often grow in compacted, oxygen-poor soils to which they respond by growing roots closer to the surface. Research with Gleditsia tri- acanthos indicated that trees in heavy soils may benefit from shallow planting, a few inches above grade. Root-Zone Temperatures The optimal range for root growth is 16- 27°C (61-81° F). Roots of container-grown trees will be exposed to higher temperatures which could be lethal. High root-zone temperatures may develop from surrounding paving, thus impairing the vigor of the tree. Root Competition Trees may be stressed from competition with other plants. Sod growing in the root zone of trees can inhibit fine root develop- ment, especially on recently planted trees. Most of the detrimental effects can be avoided by keeping turf cleared at least 12 inches away from the trunks of young trees. Pruning and Roots Substantial shoot pruning of transplanted trees used to be recommended to balance the shoot and root systems. New research indicates that severe pruning can delay the regrowth of roots, and suggests only light corrective pruning and adequate watering. To reprint material from this publi- cation, obtain permission and cite ProHort. Staking Staked trees develop smaller root systems than unstaked trees. Therefore, avoid pro- longed, rigid staking . If temporary staking is required, use a flexible method, which allows some trunk movement. References Harris, R.W., 1983. Arboriculture: Care of Trees, Shrubs, and Vines in the Landscape. Prentice-Hall, Inc., Englewood Cliffs, N.J. Schnelle, M.A., J.R. Feucht, and J.E. Klett . 1989. Root systems of trees - facts and fallacies. Journal of Arboriculture 15 (9): 201-205. Root Diseases of Native Trees George Pinyuh Cooperative Extension Service Several root diseases of native trees occur here in western Washington. They are not easy to diagnose and, by the time they are obvious on a big old Douglas-fir or western hemlock, it's usually too late to do anything about it except to remove the sick tree. Not only are the symptoms, such as chlo- rosis, reduced growth, poor needle produc- tion and declining crown similar for all of these root rots, they are also pretty much what you see when trees are suffering from other problems. Drought, poor drainage or aeration of the roots caused by grade change or soil compaction, winter damage, severe insect attack, and other things can all cause similar responses in native trees. These root diseases of our native coni- fers are prevalent in areas where homes have been built in wooded areas during the last 25 years. The disease organisms have been there all the time, even when trees may only recently have shown symptoms. Dead stumps and roots left in the ground when sites were cleared are often a repository where the fungus organisms can exist for more than 50 years. From these sites the pathogen can infect the roots of living trees. Except for the symptoms on the tops of the trees, which are often very subtle, it’s almost impossible to diagnose a potential problem. The first hint of trouble is often when a big old fir or hemlock comes down in a windstorm. It’s usually then, when the root, crown, and major buttress roots can be seen, that symptoms of disease are seen. Fomes annosus can kill both Douglas-fir and hemlock. It can attack living trees from the roots of nearby stumps and trees when spores germinate on a new stump or wound and grow down into the neighboring tree's root system. Since freshly cut stumps of healthy trees are often the beginning of the problem, some experts recommend treating all cut stumps, especially of hemlock, immediately after the trees have been felled in order to prevent Fomes spores from germinating on the surface. Borax is the stuff to use and it can be applied in the form of a borax soap available at supermarkets. If this is done in winter, cover the stump with plastic to prevent the borax from being washed off by rain. This will not eliminate the disease from an infected tree. Only stumps from healthy hemlocks can be protected with the borax. Although it’s not really easy to tell Fomes in a tree that has come down, the presence of soft and spongy roots is a pretty good diagnostic symptom. The decayed wood is often a white to cream color. Phellinus weirii is another fungus that causes much loss of conifers in our area; this disease kills a fair number of Douglas-firs. Phellinus is often called laminated root rot because of the peculiar separation of the wood into sheets at the annual rings. A brown, felt-like material can often be seen between the sheets of decayed wood. Laminated root rot-infected trees will often blow down, breaking off cleanly at the crown. The roots are not often lifted from the soil. This disease does not exhibit the soft, rotted tissue that Fomes often does. Armillaria mellea is a third common fungus that attacks the roots of local trees. This disease can kill trees of all ages whereas the two former ones seem more often to be associated with older and larger trees. Armillaria can often be diagnosed by the brown, honey-colored mushrooms that develop in groups around the bases of in- fected trees in fall. Dark brown to black, flat shoestring-like structures, looking a bit like roots, are also often present in the soil around the roots and up under the bark. Creamy, white sheets of fungus growth can also usually be found between the bark and wood of an infected tree. Sometimes dis- eased trees will have large amounts of resin at the crown and in the soil nearby. Any abnormal symptoms in trees, espe- cially big ones which might do damage if they come down, should be investigated. If it is determined that any of these root rots are present in a tree, it’s best to remove the tree. None of these diseases is curable at the stage one is likely to become aware of them, although vigorous, healthy trees can some- times isolate the pathogen and immobilize it during the early stages of invasion. Healthy trees may be able to coexist with these pathogens for long periods of time and remain disease free, but all it takes is one environmental event which puts stress on a plant for it to come under attack. Although we don’t have much control over very cold winters or long droughts, we can control some changes to the soil conditions. Adding to, or taking away, soil from the extended root system of an old tree, or laying concrete or asphalt over a tree’s root zone, or running back and forth over the soil with heavy equipment, is unsafe. Also avoid wounding tree trunks with lawn mowers or other mchines. Large animals like horses can also severely damage bark. Avoid stress- ing trees; keeping them healthy may help in keeping them vertical. The best defense against root diseases is a healthy tree. A Bristly Fir Timothy Hohn Center for Urban Horticulture Living in the Pacific Northwest, it’s hard not to take conifers for granted. The hazy, blue- green tapestry of patchwork vegetation clothing the Cascade and Olympic moun- tains may leave many of us claustrophobic about conifers. But why fight the genius of the place? The climatic conditions that nur- ture our stately coniferous forests provide us with an obviously ideal environment for cultivating interesting and exotic members of this primitive group of plants. Stalking the central California coast in 1831, Thomas Coulter was lured to the rounded peaks and rocky slopes of the Santa Lucia mountains by a tree of superb silhouette. Distinctive, even from a dis- tance, with its spire-like crown narrowing to a sharp point, the bristle cone fir, Abies bracteata, is a narrow endemic to specific locales in the Santa Lucia mountains of Monterey County, California. I recently “discovered” a threesome of Abies bracteata (“bearing bracts” on the cones) while inven- torying cold damage in the Washington Park Arboretum. They guard the boxwood (Buxus sp.) and spindletree ( Euonymus sp.) collections with a commanding stature. The rarest and most unusual species in the genus, 1 at first did not know what to make of these plants. With distinct and anomalous characteristics for a true fir, Abies bracteata is even classified separately from other species of Abies into its own sub- genus, Pseudotorreya (Liu, 1971). The phytogeny, or evolutionary history, accorded this classification makes the bristle cone fir the most primitive of true fir descendants. The needles are the largest of any species in the genus, at 3-6cm long and 3mm wide. They are sharply pointed at the tip, similar only to A. cephalonica in this regard, and shiny green above with bright white bands of stomates underneath. The winter buds are, perhaps, most anomalous in being long, 1.5-2. 5cm, and fusiform or spindle- shaped - like those of a beech ( Fagus sp.) - rather than short and rounded. The specific epithet, "bracteata", refers to the bizarre, elongated bracts which protrude from be- tween the cone scales like ominous, defen- sive bristles. The cones themselves, like those of others in the genus, are rounded and borne on the upper sides of the highest branches. A crop of cones can be so heavy as to bend down the branches and, hence, camouflage their true fir-like orientation. As the cones begin to shatter in October, the ground underneath the trees is lightly coated with shiny winged, red-brown seeds. The three bristle cone firs at the Arbore- tum were part of an original shipment of six, each 9"- 12" tall, that arrived in 1956 from Mr. John Drueker of Fort Bragg, California. Three of these were planted out in 1960 when they had reached 3' in height. These trees are now nearly 40' tall with graceful branches sweeping the ground to a diame- ter of 15'. They are symmetrically branched in regular whorls about the trunk and carry semi-pendulous branchlets clothed in stiff needles. The Arboretum specimens of Abies bracteata are densely foliated with an al- most woolly appearance. The needles are slightly 2-ranked and a shiny green to yel- low-green on top. Standing away from the trees, especially on the lighted side, the needles appear to be thinly “iced” with a bright aura of light. Upon closer inspection - lift one of the branches to examine the un- derside - one can see that the “aura" is created by distinct, silvery white bands of stomates on the undersides of the needles. Our trees are producing cones at their very tops where they may be closely ob- served with binoculars. The glistening drops of resin glued to the ends of the long, bristle- tipped bracts, should aide you in spotting them. Bristle cone firs generally flower in May, mature their cones in September, and disperse seeds in October (Lui, 1971). Very large seed crops are produced by wild grow- ing trees every 3-5 years (USDA, 1974). Seeds are collected in the fall and sown in flats to a depth of 1/4" and placed in the cold frame or cool greenhouse. Even under ideal conditions though, germination rates for true firs are usually low. Few conifers are more beautiful or im- posing than firs, and Abies bracteata is surely a regal member of this genus. Unfor- tunately, it can become very imposing in size — some garden plants in Britain reach 125', making them less suitable for home landscapes. Still, they would be magnificent specimens or groves for institutional or park landscapes. They appear to be drought tol- erant and, in fact, may resent summer irrigation. Arboretum trees have successfully withstood several severe winters with little adverse effect. Following the extreme cold of February, 1989, with a record low tem- perature of 7° F, our trees suffered only slight needle burn. No insect or disease problems have been observed on those trees. Driving along Highway 1 between Mon- terey and San Luis Obispo, you will see the chaparral-covered Santa Lucia mountains with the occasional dark patches of conifer- ous forest along the tops. Thomas Coulter, David Douglas, and others were probably guided to these bristle cone fir groves by the Franciscan Fathers of the Mission San Antonio who had long been using tree resin in religious ceremonies. To see native groves of Abies bracteata today, you must approach them from the east with the competent, albeit less pious, guidance of the U.S. Forest Service. The bristle cone fir, Abies bracteata , is a worthy and handsome conifer for land- scape use in the mild Pacific Northwest. Borrowing a summary from Donald Peattie, “ No wonder that, in regions which can grow it, this is one of the most prized conifers, imparting to estate grounds an air of dignity and spaciousness; yet, from every needle re- flecting light and cheer” (Peattie, 1953). Barbour, M.G. & Major, J., Eds. 1988. Terres- trial Vegetation of California. California Native Plant Society #9. Liu, T-S. 1971. A Monograph of the Genus Abies. Department of Forestry, National Taiwan University. Peattie, D.C. 1953. A Natural History of West em Trees. Houghton Mifflin Co. USDA 1974. Seeds of Woody Plants in the United States, Ag Handbook No. 450. Parking Parking is prepaid in University parking lots for Pro Hort. Landscape Maintenance Seminar Registration .Urban Trees: Construction Impacts WSNLA: Retail Plant Management PO Box 670, Sumner, WA 98030 .Annuals: New Approaches $13.00 $35, call WSNLA to request registration forms by Feb. 14. $13.00 Total $_ Group rates: 2-5 persons $10.50 each; 6 or more, $9.50 each. Group registrations must be accompanied by ONE check or purchase order, at least one week in advance. Make checks payable to the University of Washington; receipts available at the door only. Mail payment and registration to: Center for Urban Horticulture/ProHort, University of Washington GF-15, Seattle, WA 98195. For information, call 545-8033. Name Address City State Zip Day Phone Evening Phone Zoned Out on Hardiness Dr. Clement Hamilton, Center for Urban Horticulture “Seattle is, of course, in hardiness Zone 8.” “Oh, yeah? We’re in Zone 9!” “You’re both nuts — we’re Zone 5!” So run similar discussions whose disagreement is grounded in the fact that not one, but three, hardiness zone systems are in common use in the western United States: the Arnold Arboretum, the USDA, and the Sunset systems. What are the differences? The Arnold and USDA zone systems are similar in that they are based only on average annual minimum temperatures. They reflect the belief that low winter temperature is the most stressful condition that a plant can encounter, and limits the geographic range in which a plant can be grown successfully. The two systems differ in how they divide the range of minimum temperatures into distinct zones. The USDA does it by 10°F increments, while Arnold recognized greater sensitivity in the -10° to +10° range, so Zone 2 is -50° to -35° whereas Zone 5 is -10° to -5°. The two systems are summa- rized in Table 1 . Notice that Arnold’s Zone 4 is equivalent to USDA Zone 5, but that by Zone 8, the two systems are identical. Their differences aside, neither system is satisfactory for North America west of the Great Plains, because other large-scale geo- graphic factors begin to assert their importance. They include aridity (arid seasons of varying lengths, severity, and timing), elevation (which influences atmospheric pressure, which in turn af- fects plants’ gas exchange), and potential evapotranspiration (the rate at which water is removed from the system). Eastern North America is relatively uniform in these factors, so the Arnold and USDA systems are useful, but they fail in the West, where mountain ranges, oceanic winds, and seasonally shifting atmospheric pres- sure zones make the prediction of plant success a risky business. There are many localities in North America with low winter temperatures similar to those of Puget Sound. There are places with no arid season (Oklahoma City, with low rainfall; Tucumcari, NM, with high elevation; and Washington, D.C., with high rainfall); places with a 2-3-month arid season (such as Seattle); places with a 4-5-month arid season (Ashland, OR, with summer drought; and Roswell, NM, with winter drought); and places with as many as 10 arid months per year (Socorro, NM). These are all in the same zone by the two zone systems described above! The editors of the Sunset Western Garden Book recognized this dilemma and enlisted the aid of climatologists and horticulturists in devising a hardiness zone system that would be useful in the West. Their 24 climate zones are based on latitude, elevation, tempera- ture, and water balance, supplemented by the knowledge of suc- cesses and failures of selected “indicator plants.” The result is ar- guably the best hardiness zone system now in use for landscape plants. This is not to say that conditions within a given zone are identical, however; Astoria, OR, and Seattle are both in Sunset Zone 5, but the former experiences less aridity in the summers. One focus of research in the Hyde Hortorium at the Center for Urban Horticulture concerns plant hardiness or “physiological range.” We are asking two questions: "For a given plant, which large-scale geographic factors are most important in determining success or failure? " and "Is there enough consistency among most plants to enable us to devise a more precise, predictive system?”. Until we have something better to go on, readers are advised strongly to use the Sunset system. Whatever you do, avoid confusion by identifying the system you’re using: “Sunset Zone 5.” “Oh, 1 thought you meant Arnold Zone 5!” Table 1: Comparing USDA & Arnold Zone USDA Arnold Zone USDA Arnold 1 Below - 50°F Below -50°F 6 -10° to 0° -5° to 5° 2 -50° to -40° -50° to -35° 7 0° to 10° 5° to 10° 3 -40° to -30° -35° to -20° 8 10° to 20° 10° to 20° 4 -30° to -20° -20° to -10° 9 20° to 30° 20° to 30° 5 -20° to -10° -10° to -5° 10 30° to 40° 30° to 40° University of Washington, GF-15 Seattle, WA 98195 Nonprofit Org US Postage PAID Permit 62 Seattle, WA CENTER FOR URBAN HORTICULTURE Center tor Urban Horticulture 350 1 NE 4 1st Street University of Washington. GF-15 Seattle. Washmaton 98195 206 5 45-8033 Winter 1990