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Plant Stewardship

Caring for the Arboretum Trees and Plant Collections

Current Events and News


The Arboretum's plantings constitute one of the premier woody plant collections in the United States with nearly 4400 different kinds of plants. These plantings are displayed among trees of our native Puget trough hemlock-cedar forest zone. The retention of native trees is part of WPA's naturalistic landscape style. This style also poses special challenges and needs in providing for the care of both native and collected plants. The maintenance and care of these plants is closely tied to our mission of education, conservation, and display. Both University and City staff work hard in caring for the Arboretum's landscape. Conservation of the plant collections in this highly utilized facility includes management for insect and disease pests, weak and dead plant removal, hazard reduction, plant replacement, and landscape restoration.

The Arboretum employs a holistic approach to managing plant health problems, combining the use of carefully timed, least toxic control applications, cultural practices to improve plant vigor, and the removal of severely affected plants beyond restoration. Extensive monitoring and follow-up evaluations are a critical part of this work.

More information about plant health care and the pest management program here at the Washington Park Arboretum.

The arboriculture program covers care and management of collection and native trees. The goal is to reduce potential hazards through inspections and preventive work, as well as conserving the plant collections. This work includes pruning and training for young trees, cabling and bracing to preserve scaffold limbs in large trees, pruning and removal. The effects of root rot diseases as large trees age are a major contributor to hazards and actual failures in the larger native trees, particularly big-leaf maples.

Crabapple Meadow Improvement

Cedars to be removed for Crabapple Meadow Improvement

The four Western Red cedars shown above are designated to be removed late June. The increased light will benefit plant collections on SE facing slope of Woodland Garden. Also, removal of these cedars will create a connecting entryway between Woodland Garden and Crabapple Meadow. The cedar logs will be salvaged and used for the roof beams of the Pacific Connections Gardens Interpretive Shelter. Arboretum Drive will be closed during these removals for public safety. Closure signs will be posted one week in advance. For further info., contact Fred Hoyt, UWBG Grounds manager at 206-543-3137

December 2006 Storm Illustrates Dynamics of Nature
at Washington Park Arboretum

This winter’s wild storm left Washington Park Arboretum (WPA) with 65 trees affected, and 37 total losses. The loss ratio of accessioned to native trees measures 2:1. While the destruction appears devastating, it’s important to note that collections at WPA are dynamic like nature itself. It is through nature’s intervention, as well as our own, that change occurs. For example, arborists sculpt “snags” for wildlife out of recently broken trees. Logs of fallen trees now line and support trails in WPA’s Pinetum. Resulting new spaces and increased light improve conditions for existing specimens, and provide opportunity for new plantings. We can look forward to renewal as the Pacific Connections Garden progresses.

assessing strom damage'The effects of a blustery December add up. Hours spent by horticultural staff exceed 700 for storm clean-up efforts. The enormous project takes crew away from scheduled tasks such as tree care, IPM (Integrated Pest Management) and new plantings. If you’d like to lend a hand, volunteers meet to garden on Tuesdays, 12:30-3:30. No background in gardening is necessary. Please contact David Zuckerman, Lead Horticulturist, at 206.543.8008 or dzman@u.washington.edu.

Extreme events like our recent storm can mislead people and frighten them into removing valuable, safe and healthy trees. If you have concerns about a tree, have it assessed by an arborist certified by ISA (International Society of Arboriculture). You can find a qualified local arborist by contacting PlantAmnesty.org, or the PNW Chapter of ISA.

2005-2006 Planting Season Report

The 2005-2006 planting season (Oct-June) at the Arboretum is now complete. The Arboretum horticulture staff installed over 80 accessioned plants, the majority being tree forms. A breakdown of 45 taxa (includes cultivars); 32 of which are species, 5 natural subspecies and varieties, and 8 cultivars and hybrids. These numbers do not reflect the non-accessioned amenity (herbaceous) and restoration plantings in 2005-2006. For example, more than 50 native trees, representing 8 species, were planted by a UW Restoration Ecology Network (UWREN) capstone class. The restoration plot is in the Puget Sound lowland riparian zone, located at the mouth of Arboretum Creek in the southwest lagoon area.

Overall, significant additions were made to our iconic Oak, Maple, Mountain Ash and Magnolia collections. Also, two landscape shade trees, Aesculus x arnoldiana ‘Autumn Splendour’ and Fraxinus angustifolia ‘Raywood’, were planted around the upper Woodland Garden pond to accentuate the garden’s fall colour display. These trees will eventually provide shade for many of the Japanese maple canopies sensitive to the harsh summer sun.

Several of our new plantings were provided via private donation. Our new north entry pylon planting along Lake Washington Blvd includes a tree donation of a beautiful 7’ Golden Chinquapin, Chrysolepis chrysophylla. Although this tree was transplanted rather late in the season, it appears to be adjusting to its new home just fine.

Attention at the Arboretum is now focused on making sure that all the 2005-2006  plants are well established. The Irrigation/ New Plant Care crew is running full bore (10 hr days) trying to keep up with all the watering and maintenance needs.

For further information, please contact David Zuckerman, UWBG Horticulturist at 206.616.4050 or zucked@u.washington.edu
    Acer sterculiaceum ssp. franchetii
Acer sterculiaceum ssp.franchetii – 20’ maple from Central China.
Lindera triloba
Lindera triloba – Japanese spicebush. Related to the US native sassafras.
    Magnolia delavayi

     
Magnolia delavayi – Chinese evergreen magnolia.
    Magnolia 'Butterflies'

     
Magnolia ‘Butterflies’ – Magnolia hybrid. Touted as one of the better yellow flowering types.
Sorbus rehderiana
Sorbus rehderiana – Dan Hinkley, China expedition, Mountain Ash.

Hazard Tree Removals

There are three hazard tree removals scheduled during Arboretum Dr closure (Irrigation Mainline project): 2 hemlocks and 1 bigleaf maple. All are located in the Woodland Garden vicinity. The hemlocks will be removed Dec 13 w/ the assistance of UW arborist and equipment. The bigleaf maple will be removed February 13 by a contractor. Up to 10 new Acer palmatum cultivars (Japanese maples) will be planted on the hillside presently occupied by the bigleaf maple.

Any further questions, please contact me via e-mail or number below.


David Zuckerman
Horticulture Staff Supervisor
UW Botanic Gardens
Washington Park Arboretum
VM: 206.543.8008
FX: 206.616.2871
dzman@u.washington.edu

Hazardous Bigleaf Maple

Adelgid Predator Study

Researchers at Virginia Polytechnical Institute are researching biological control of the hemlock woolly adelgid, an aphid-like creature killing eastern hemlock forests in the United States and Canada .
A small beetle and predator of this adelgid has been discovered in the western United States . These ‘pillow cases' in the trees are part of a study to determine the effect of this beetle predator on the adelgid populations. PDF Flyer

Buddleja davidii in the Arboretum

Buddleja davidii, introduced from China around 1900, has become invasive in western Washington, especially along our rivers and streams. This species and its cultivars (cultivated varieties) were recently placed on the Washington Noxious Weed List and mandated for control in some areas. Because the Washington Park Arboretum supports the conservation of Washington's lands and vegetation, we have decided to remove all plants of Buddleja davidii from our collection. All other species and hybrids of Buddleja will remain at this time.

New Oaks Collection Display

This fall, new additions to our Oak Collection will be made, representing 5 North American oak species, 2 Eastern U.S. and 3 Western U.S.:

  • Quercus alba (White Oak): Our most famous and largest growing oak in the U.S. Known to attain over 160’ x 30’ dimensions.
  • Quercus muhlenbergii (Chinquapin Oak): Has leaves like those of chestnuts.
  • Quercus agrifolia (California Live Oak): Oakland, CA is named after this oak.
  • Quercus chrysolepis (Canyon Live Oak): In its native state, this Californian oak is unsurpassed in majestic beauty.
  • Quercus engelmannii (Engelman Oak): Live oak native to S. Californian mountain ranges.

Master Plan Progress: Pinetum Development Update

Fall and winter project work is now almost complete in the Pinetum. A few trees remain to be removed and there are several stumps to grind before spring. The City Parks Dept. is currently involved in trail restoration from the Stone Bridge south to Boyer Ave. This work includes regrading and graveling path surfaces, installing a new culvert under path where it passes over drainage tributary into Arboretum Creek, stormwater diversions and other path surface treatments. Unfortunately, the red clover hydroseeded over old stump areas did not take, so we will need to reseed this spring. Lastly, the landscape architecture firm, The Berger Partnership PS, has completed the Pinetum Wayfaring Layout and Materials Plan. Upcoming project work will include (spring-fall ’04):

  • Curatorial and horticultural planning for new conifer collections
  • Installing interpretive sign for Dan Evan’s Coast Redwood
  • Soil and drainage improvement during summer, i.e. tillage, adding compost, etc.
  • Begin implementation of wayfaring plan this summer
  • New plantings in Fall 2004

 

Master Plan Progress: Oak Collection Improvements

Our oak collection is one of the top three taxonomic collections nationally, displaying over 55 species of 150 potential taxa. Maintaining this vital collection, as outlined in the master plan, is a high priority.

The evaluated collection is based on horticultural condition and curatorial value. Several collections were removed based on report results. Collection conditions were also improved by the removal of impacting natives competing with the oaks for space, light and water, and by pruning the deadwood in the oaks. Site and interpretive improvements included creating a defined space to view oaks, opening view corridor from Foster Island Dr., cedar snag and log left for habitat enhancement, and turf renovation.

No special funding is required. All work will be accomplished in-house by UW and City grounds and curatorial staff. Also, volunteer arborists sponsored by Plant Amnesty assisted in pruning the oaks.

Oak Collection Removals

No removals are currently scheduled.

Other Collection News

The Arboretum Shoreline Project is now complete and the area is once again open to the public. More info on this project can be found on our Shoreline page.

 

 

For further information about stewardship of the Washington Park Arboretum, please contact WPA Horticulture Staff supervisor David Zuckerman at zucked@u.washington.edu


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