Tree Care and Maintenance Archive

Emerald Ash Borer
Summer 2018

Image courtesy of Leah Bauer, USDA Forest Service Northern Research Station,

The emerald ash borer (EAB) is an invasive insect from Asia believed to have come to the United States in the 1990s through international shipping. The EAB’s primary food is ash trees and when an EAB eats, ash trees die. All 16 North American ash species, including our native Oregon ash (Fraxinus latifolia) are vulnerable; the Union for Conservation of Nature has declared five U.S. ash species as “critically endangered.”

EAB first started killing ash trees in Michigan, but now EABs have been detected in 35 states, despite efforts by regulators to contain them. Since 2002, this exotic insect has killed over 100 million trees throughout the country, causing more than $3.5 billion dollars in damages. While EAB has not been detected in Oregon yet, it is moving rapidly across the U.S., as far west as Boulder, Colorado. The transportation of infested firewood during the summer camping season is thought to be a main factor in the spread of EAB.

EAB can cause significant damage to Oregon’s urban and rural ecosystems, including along streamsides where many wild ash trees grow. “Wild ash forests and urban ash trees face a threat that has cost other states billions of dollars.  Similar to wildfires, floods and other catastrophic threats, it is best to detect EAB quickly and deal with it swiftly,” said Wyatt Williams, the Oregon Department of Forestry’s invasive species specialist. Since 2006, the Oregon Departments of Forestry and Agriculture, and the U.S. Department of Agriculture have surveyed Oregon for EAB and found none…yet. 

Oregon is one of the few western states that has a statewide EAB plan to protect and limit harm to the state and prepare its communities and citizens. The Oregon Invasive Species Council facilitated the plan’s development. Funding for this project was provided by the U.S. Forest Service Region 6 Western Competitive Grant for the “Forest Pest Detector Program.” The Oregon Readiness and Response Plan includes a statewide risk assessment, methods of early detection, and quarantine and communication plans.

Next time you head out for a family camping adventure, please remember to buy your firewood where you burn it! Check out these resources to learn more:

Don’t Move Firewood

Identify Invasive Pests

Oregon Forest Pest Detectors 

EAB Readiness and Response Plan for Oregon 

To report a suspected invasive species, visit or call 1-866-INVADER.

Pruning Young Trees
Spring, 2018

Now that you’ve planted the right tree species in the right place, young tree structural pruning is one of the most important things you can do. Thoughtful and proper pruning early in the life of a tree can reduce the need for maintenance over time, improve structure and strength, and perhaps increase the tree’s lifespan. When the tree is first installed, limit pruning to the removal of dead and broken branches only. The tree needs two to three years to recover from transplanting shock, and as much foliage as possible during this time to create and store energy through photosynthesis while its roots become established and begin to expand. In years three or four, you can begin to remove defective branches and thin excessive branches. Around years five to seven, you’ll want to select the lowest permanent branches and check for even branch spacing throughout the crown. After that, inspect the tree early each spring and prune dead and defective branches as needed. Remember, every pruning cut should be made for a purpose and with good intention. It is critical that you use the right tools and make proper cuts to promote wound closure and avoid damage. When in doubt, consult with an ISA Certified Arborist, and be on the lookout for free annual pruning workshops  hosted by the City’s Urban & Community Forestry program. Check out these resources to learn more:

Brochure – Pruning Young Trees by the International Society of Arboriculture

Webpage – Annual Tree Pruning Steps from Planting to Maturity by the Arbor Day Foundation

Video – Training Young Trees by Larry Costello and Ellyn Shea



Tree Related Storm Damage
Winter, 2018 

Did you know that nearly 15 times more trees failed during the Columbus Day storm in October 1962 than during the eruption of Mount St. Helens in 1980? While the Columbus Day storm was exceptional, with wind gusts reaching 116 mph in downtown Portland, tree-related storm damage is not uncommon in our region. This time of year, saturated soils, strong winds, and freezing rain may lead to failure of part or all of a tree, even a seemingly healthy one, which may result in lasting impacts to your landscape. However, it is important for property owners not to make hasty decisions during clean-up that can threaten their own personal safety or exacerbate property damage. There are simple steps to follow in response to tree-related storm damage to stay safe and get your landscape back in order. Check out these resources to learn more:

Video – Tree Care Tips: Storm Damage and Trees by Stihl USA

Brochure – Weathering the Storm: Safe Response to Tree-Related Storm Damage by the International Society of Arboriculture

Webpage – Tree First Aid After a Storm by the Arbor Day Foundation


Fall, 2017

Fall is a great time for planting new trees in Oregon. Selecting the right tree species and the right planting location is a decision that can have an impact on your landscape, and perhaps your neighborhood, for decades to come. There are many factors to consider in selecting the most suitable and desirable tree species for your site, and following simple steps for installing a new tree will help to avoid common problems caused by improper planting. Check out these resources to learn more about selecting and planting new trees:

OSU Publication: Selecting, Planting, and Care for a New Tree, EC1438, March 2016
iOS and Android App: A New Tree by Oregon State University
Species Guide: Right Tree in the Right Place
Video: How to Plant a Tree Properly


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Summer, 2017

Trees and turfgrasses are commonly planted together in residential landscapes, but are not so easily compatible. They compete for water, sunlight, nutrients, and root space. Tree trunks are easily damaged by lawnmowers. And, what about those expansive surface roots damaging your lawnmower blades?

Understanding how to better manage the competition will help you take advantage of the variety of benefits trees and turfgrasses can provide. For example: surface rooting throughout lawn areas can be prevented with proper tree species selection, soil improvements, and providing a slow, deep, and infrequent watering beneath tree canopies; a grass-free ring of bark mulch is a good alternative around tree trunks to help keep lawnmowers away, in addition to a variety of other benefits the mulch will provide; and, new varieties of shade tolerant grasses are becoming more available.

Learn more about trees and turfgrasses by visiting these sites:

Trees and Turf Brochure ( Tree Owner Information)
Tree roots coming to the lawn surface can be a real headache (Seattle Times, Ciscoe Morris, October 29, 2015)
Mechanical Damage to Trees: Mowing and Maintenance Equipment (Purdue Extension, FNR-492-W)
Tree Watering (Arbor Day Foundation)
Plant Guide: Water-Efficient Plants for the Willamette Valley

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Spring, 2017

English ivy is the most common invasive plant in Lake Oswego. It is an aggressive species with no natural enemies that grows and reproduces quickly, outcompetes native plants like wildflowers and ferns, and has vines that commonly grow up tree trunks with detrimental effects. English ivy competes with trees for water and nutrients, deprives tree bark of normal contact with air and microorganisms, and increases susceptibility to wind stress and the risk of canopy or whole tree failure.

Property owners can remove ivy from trees by cutting the vines at chest height in a ring around the trunk with pruners, loppers or saws. Pull the lower portion of the cut vine off of the tree trunk carefully to avoid bark injury, and pull or dig out the attached roots. Clear a 3- to 5-foot ring around the base of the tree to help prevent or postpone re-growth up the trunk. The upper portion of the vines can be left on the tree because it will die back.

Learn more about the detrimental effects of English ivy and how to remove it by visiting these sites:

Factsheet: Ivy Removal in a Home Landscape

Video: How to Remove Ivy

Explore: The Ivy Files


Seasonal Tree Care Tips: Preparing Trees for Fall and Winter

Fall is a great time to be prepare your trees for the winter weather ahead. With leaves falling from trees, branch structure and defects are easier to see, so it’s a great time of year to have your trees inspected by an ISA Certified Arborist. Branches may need to be pruned, cabled or braced to help prevent storm damage. Fall is also a great time of year to mulch and fertilize. Mulch helps to insulate the soil and retain moisture, but too much mulch can be harmful. Generally, a 3” deep ring of mulch in a 4’ circle around your tree is sufficient, but don’t pile mulch against the tree trunk. Fertilizer should never be applied without first obtaining a soil test to check for nutrient deficiencies.

Visit these sites to learn more about preparing your trees for winter:

Cabling & Bracing Trees as a Corrective Measure

Mulching Trees & Shrubs

A Guide to Collecting Soil Samples

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FALL, 2016

Trees provide desirable benefits in the landscape, but may become hazardous when they have defects resulting in increased failure potential and are located within striking distance of targets—such as people, vehicles, buildings, or other infrastructure—that could be injured or damaged by tree failure. Reasonably assessing the potential risk of injury or damage that a tree may cause and managing to reduce risk is called Tree Risk Assessment. The Tree Risk Assessment Process involves a systematic evaluation of an individual tree along with review of site use, and is a specialized area of expertise that should be undertaken by a trained professional. An ISA Tree Risk Assessor Qualified Arborist can assign a hazard risk rating to your tree and provide management recommendations to reduce risk, such as relocating potential targets, pruning to remove defective parts, or whole tree removal. It is a property owner’s responsibility to ensure that their trees are reasonably safe and to manage their trees in order to reduce risk. Visit these sites for tips on recognizing tree risk and know when to contact a professional:


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