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Attack of the Zombie Trees

Halloween is upon us! Do you know what’s spooky? Zombie trees.

Zombie trees are those that are still standing upright but are dead inside from a variety of environmental factors; disease, insect infestation, improper pruning and lack of water. They might look alive but these ticking time bombs will eventually topple over, posing a real danger to both the public and your property. If you have a zombie tree, a strong wind could easily send it toppling over and cost you thousands of dollars in damages – to your yard, roof, vehicles or wherever it may land.

Symptoms of a zombie tree:

  • Bark that is decaying, missing or showing breakage
  • Loss of leaves
  • Dead and/or falling branches

“Because we have early fall snows and high winds in Colorado, Denver residents should always be mindful of the health of the trees on their property,” said Sara Davis, Urban Forestry Program Manager in the Office of the City Forester.

If you live in Denver and own property, you are responsible for:

  • Cleanup of debris from trees on private property and from trees within the public right-of-way adjacent to their property. (Limbs on the ground are considered debris. Property owners can hire any company to haul limbs away – for this type of work, the company does NOT have to be a licensed tree contractor.)
  • Pruning needs of private property trees and trees within the public right-of-way adjacent to your property.

Unfortunately, there are times when the safety of the public necessitates that the work be completed immediately and Denver Forestry cannot allow time for the property owner to find a licensed tree professional. When a tree or limb is blocking safe access to the street or right-of-way, Denver Forestry has an on-call contractor remove the limb or tree and bills the property owner for the work.

There are many tree professionals that are licensed by the Office of the City Forester who can safely remove a zombie tree from your yard, sparing you the costly expense of a fallen tree. Before you hire someone to remove your zombie tree, ask if he or she has a Colorado State Department of Agriculture tree service license.

Take Advantage of the Fall Color Change

As pumpkin spice lattes make their debut at our local coffee shops, so do the colors of fall. The leaves of trees in our parks and backyards are beginning to change from green to yellow, purple and plum – a clear sign that winter will soon be here. 

Ash leaves

Take advantage of these vibrant signs and Be A Smart Ash.  
With the Emerald Ash Borer confirmed in the City of Westminster, directly neighboring the City of Denver to the west, now’s the time to Be A Smart Ash. Use the vibrant fall color change as your guide and get outside; look for the most colorful leaves, then use these telltale identifiers to confirm you’ve found an Ash: 

  • Compound leaves: A simple leaf is defined as a single leaf that has a bud at the base of the leaf stem. Conversely, a compound leaf (the sort you’re looking for) is defined as having more than one leaflet per leaf connecting to a stem that has a bud at its base. Ash tree leaves typically have 5-9 leaflets per leaf. 
  • Opposite branching: By opposite branching, we mean the branches protruding from tree limbs have a mate protruding from the exact opposite side of the same limb. Only ash, maple, dogwood and horse chestnut trees have opposite branching. 
  • Diamond-pattern bark: While this identification method may not be as helpful when it comes to young ash trees (they typically have smoother bark), the bark on more advanced ash trees tends to have distinct diamond patterns. 

Once you’ve confirmed the tree is an Ash tree, make sure you don’t see any pesky green bugs around, or any wavy trail lines or d-shaped holes in the trunk. Multiple visuals can be found here. Hopefully, the tree is healthy, in which case there are multiple options to help keep it that way. 

If the tree is on public property, look for a tag that says “This Ash Is Covered” to know it’s been treated by the City Forestry Department. More information on the city’s treatment and replacement plan can be found at BeASmartAsh.org. If the tree is on your personal property, check out your next steps here. 

Think you might have an EAB infestation? Take a lot of pictures and contact the City Forester at forestry@denvergov.org or 720.913.0651. 

Find the Smart Ash Superhero Around Town

Fighting Emerald Ash Borer

The Smart Ash Superhero is making the rounds to local libraries, recreation centers and public spaces to introduce more Denverites to the Emerald Ash Borer (EAB) and ways to Be A Smart Ash. Be on the lookout for the Smart Ash display and let us know where you see him by tagging @BeASmartAsh or using the hashtags #EAB and #BeASmartAsh on Twitter.

Join our effort to save Denver’s ash trees by talking to your neighbors, friends and co-workers about EAB and encourage people to visit BeASmartAsh.org for more information.

Emerald Ash Borer Detected in Broomfield

Photo courtesy of Colorado State Forest Service

The Emerald Ash Borer (EAB) was confirmed in the City and County of Broomfield, northwest of Denver, on Aug. 20, 2019 – the first confirmation of EAB in Colorado outside of the federal quarantine that primarily encompasses Boulder County.

A Broomfield resident familiar with the appearance of EAB due to Broomfield’s proactive public education campaign noticed a suspicious insect on their personal property near 136th Avenue and Main Street and contacted the Broomfield city forester. It is not known whether the pest arrived by natural spread or human transport such as firewood.

At least 15% of all urban and community trees in Colorado are ash species susceptible to being killed by EAB. EAB attacks and kills both stressed and healthy ash trees and is so aggressive that trees typically die within two to four years after infestation. While EAB has not yet been detected in Denver, it could already be here.

Wondering what you can do to protect your ash? We have resources to help you review options.

Sustainable Urbanism and Tree Care

Professor Austin Troy, photo courtesy of University of Colorado Denver

Austin Troy is Professor and Chair of the Department of Planning and Design at the University of Colorado Denver. As part of the Master of Urban and Regional Planning (MURP) faculty, Troy is one of the most respected researchers in the planning field. The Smart Ash team recently caught up with him to discuss sustainable urbanism and tree and lawn care during the hot summer months.

Question: How would you explain sustainable urbanism and regional sustainability to the average Denverite?

Answer: Urban sustainability is a field of study that examines the interaction of social and environmental systems in cities. I mainly work with green infrastructure – including mapping the location of trees and vegetation, prioritizing where they should be planted, and characterizing their many benefits to the city. As for regional sustainability, I like to point to the Green Building ordinance as an example. City voters passed this initiative in 2017 and it’s the most aggressive greening ordinance in the country right now.

Question: What’s your opinion of Denver’s current tree canopy?

Answer: It’s very impressive and vast when you consider how much the city has grown in the past century. Much of the current canopy can be attributed to decisions that were made 70 to 100 years ago by Mayor Speer and other Denver leaders.

Question: For homeowners, the million-dollar question is (water time slots and allocations notwithstanding) how much should you water your lawn? How do trees affect water needs?

Answer: Nobody quite understands this and the short answer is that it’s complicated. Tree shade is really important to overall irrigation demands. My team is in a partnership with Denver Water and when we look at their data we see that people who have mature tree canopy over grass can theoretically use less water in many cases than those with only grass. Broadly speaking, shade can offset your water costs. This may be because lawns without tree shade can get desiccated in the direct sun and homeowners try to compensate by overwatering. That said, we also think older trees are tapping into some of Denver’s older clay pipes for water. It’s a leaky infrastructure. Also, as people water their lawns, much of that water goes back into groundwater where more mature trees with deeper roots can reach it. There are a lot of factors to consider.

Question: What type of treatment or care should a healthy tree receive in the summer months?

Answer: It’s always wise to lean on an experienced arborist for this guidance. It depends on the species but most need to be pruned. Younger and smaller trees often require more water.

Question: What is your team currently working on?

Answer: We’re heavily researching the benefits and the costs of trees and vegetation in Denver. We’re interested in a wide suite of things, ranging from heat mitigation to storm-water mitigation to rainfall interception to socioeconomic factors like crime and property values. The goal is to provide the tools to help ensure that the benefits of trees are fairly and equitably distributed throughout Denver.

Question: What are you up to in your own yard?

Answer: I recently hired a landscape architect to help me bring my vision to life. Up until now I had just been maintaining my yard and not thinking outside the box. Now I want to introduce more native, low-water plants and interesting landscape features. Hopefully, there will be a lot less space that requires irrigation. I’m excited about it!

Apply for a Free Tree

Do you have room for a new tree? Being a Smart Ash means that we plant new trees before losing established ones to the EAB. In fact, Denver Parks and Recreation wants to help you plant a tree. If you have room in the public right-of-way next to your property, you may even be eligible to have a free tree planted for you! Learn more here.

Denver’s Ash Trees Ready for Second Treatment

If you were out and about in Denver in 2016, you likely saw hundreds of ash trees wrapped in plastic that said, “Be A Smart Ash.” Denver Parks & Recreation’s Office of the City Forester treated public right-of-way ash trees adjacent to private properties throughout the city to prevent an Emerald Ash Borer (EAB) infestation. Although the treatment of ash trees by a tree care professional is 90% effective, treatment must be repeated every two to three years to remain successful. With this in mind, we will be treating these trees again.

Healthy ash trees that are 12 inches and larger in diameter at four feet off the ground were put on a list for potential treatment. From this list, a number of trees were randomly selected in each neighborhood to be treated in either 2016, 2017 or 2018.  Because trees require treatment every two to three years, we’re revisiting the 2016 trees now. Every ash tree scheduled to be treated was examined by a city arboreal inspector to determine if it was a good candidate for treatment.

EAB is a destructive pest that kills ash trees and poses safety and financial risks. However, this treatment, when done in advance, is more than 90% effective in preventing tree death.

photo courtesy of @watersa on Instagram

Risks of avoiding treatment Include:

  • Ash trees killed by EAB become very brittle and can break easily. Dead ash trees are dangerous to you and your neighbors and can be expensive to remove.
  • You are responsible for removing infested or dead EAB trees on and adjacent to your property, so treat your tree!
  • EAB has the potential to destroy Metro Denver’s 1.45 million ash trees – roughly 1/6 of Denver’s trees – significantly impacting our precious tree canopy.

Trees are critical for our overall quality of life. They produce oxygen, reduce smog, cool our neighborhoods and homes and increase our property values. Join our effort to save Denver’s ash trees by talking to your neighbors, friends and co-workers about EAB and encourage people to visit BeASmartAsh.org for more information. To see which ash trees are being treated and those that are candidates for future treatment, visit BeASmartAsh.org/treatment-schedule.

Removing and Replacing Your Ash Tree

One of the four recommended treatment options for a tree infected with emerald ash borer (EAB) is to remove the tree and replace it with another species that can grow well in Colorado. Though the EAB has yet to be found and confirmed in the Denver Metro Area, the removal and replacement option is both cost-effective and convenient for homeowners.

Step one is removal of the ash tree and step two is replacement. While it sounds easy enough, hiring a tree professional will make this process significantly easier. When searching for a tree professional, this list of Certified Smart Ashes approved by the Denver City Forester is a great place to begin your search. There are many tree professionals that are licensed by the Office of the City Forester who can lend a hand.

We connected with the wise folks at Denver Parks & Rec to ask for their recommendations for tree replacements. We asked for suggestions for species that will easily thrive in our local climate when provided adequate care. Drumroll, please…

Smaller Trees | Less than 30-feet high

Amur Maackia – photo courtesy of Oakland Nurseries
Any redbud – photo courtesy of Arbor Day Foundation
John Pair maple – photo courtesy of Iowa City Landscaping
Peking lilac – photo courtesy of Forestfarm
Three-flower maple – photo courtesy of Heritage Seedlings

Shade Trees | 30-feet and taller

Espresso Kentucky coffeetree (without seeds) – photo courtesy of Your Garden Sanctuary
Prairie expedition elm – photo courtesy of Laidback Gardener
Tuliptree – photo courtesy of Tennessee Wholesale Nursery

Trees in the approved list are those which, given proper and consistent maintenance including supplemental irrigation, proper pruning, and avoidance of chemical contaminants, will be assets to Denver’s beautiful urban canopy. You can also explore the approved list in its entirety.

Denver Botanic Gardens Spring Plant Sale


Spring has sprung and Denver residents are preparing their gardens for the summer months ahead. While we’re certain you have flowers on the mind, your trees deserve your love and attention too! The Be a Smart Ash team will be on-site next month at the Denver Botanic Gardens Spring Plant Sale to discuss all your questions about ash trees. Ask us about our ruthless plan to foil the invasive Emerald Ash Borer (EAB) and take a selfie with the fearless and rugged Smart Ash.

The city of Denver manages the ash tree population in public spaces and in the right-of-way, but any ash trees on your property are your responsibility. The fight against EAB is real as it’s only a matter of time until they are found in our beautiful city. You can have a tree care professional treat your tree or remove and replace it with one of these City Forester-approved trees (some of which you might be able to get for free). With your help, we can maintain the long-term stability of our urban canopy.

The event details are below. As always, you can follow us on Twitter at @BeASmartAsh in the meantime. We look forward to seeing you!

What: Denver Botanic Gardens Spring Plant Sale
When: Saturday, May 11 from 8 a.m. to 5 p.m.
Where: 1007 York Street, Denver, CO 80206
Cost: Admission is free and prices vary for plants – both cash and credit cards are accepted
Bring: A cart, wheelbarrow or wagon to haul your treasure
Enjoy: Complimentary valet to load your purchases directly into your car
Sneak peek: Over-achievers who want a sneak preview of the plants available for sale on Saturday can attend a ticketed event on Thursday, May 9 from 4 to 8 p.m. at the gardens. Tickets sell out quickly and cost $45. You’ll have access to expert horticulturists, appetizers, wine, beer and plants.
Questions? 720-865-3500

Be A Smart Ash & Denveright

Here at Be A Smart Ash, it’s our job to create a defense plan that protects Denver’s 330,000 ash trees from emerald ash borer (EAB), the most destructive forest pest in U.S. history. It has already caused a billion dollars’ worth of damage in more than 30 states and parts of Canada.

But our job goes much deeper than that.

The Be A Smart Ash movement is one part of the much larger process that we know as Denveright, an unprecedented opportunity to align citywide plans to guide future investments so that the whole is greater than the sum of its parts.

Thousands of Denverites shared their unique perspectives on what makes Denver great and how it can evolve to improve even more. You shared your voice in many ways — by attending meetings and workshops; taking online map-based surveys; talking with the Denveright street team at festivals, community events and transit stations; joining a Community Think Tank; and more.

As it relates to our parks, recreation and urban forest, you made it clear: You view these places as vital components of a complete community. And it’s our job at the Office of the City Forester to deliver them for you.

Enter the Game Plan for a Healthy City and Blueprint Denver.

Game Plan for a Healthy City

This is a new citywide parks and recreation plan for the next 20 years that proclaims easy access to parks and open space is a basic right for all residents. The Game Plan provides a roadmap for supporting and building our parks, recreation programs and urban forest to serve the needs of all Denverites in the face of ongoing population growth and climate change.

So what challenges are we facing that the Game Plan addresses? There are six big ones:

  • Drought & Flooding: Roughly 11%, or $2.7 million, of our annual parks operating budget goes toward irrigation. The less drought-tolerant landscape could be lost. Droughts and flooding are both projected to increase in the future.
  • Parks Not Keeping up With Growth: From 2010-2016, the city experienced 11% growth while park space grew at a slower rate. Denver’s park inventory of nine acres per thousand residents is well below the national average of 13 acres per thousand residents.
  • Growth Economic Challenges: Deferred maintenance totals are $119 million and nearly one in six park assets are in poor condition. Expenses have significantly outpacing funding growth.
  • Limited Access to Nature: Many neighborhoods lack walking access to places where they can experience nature. Mountain parks are difficult to access for families without a car.
  • Obesity is Rising: Nearly one in six children is obese and 52% of Denver’s residential parcels are not within a 10-minute walk of a playground.
  • Threatened Urban Forest: Last but not least, Denver’s urban tree canopy is one of the lowest in ranked cities and one in six trees are threatened by EAB.

Are these big challenges? You bet. But as we like to say around here, who wants to be a Debbie Downer when you can Be A Smart Ash? We have a 20-step plan for the next 20 years to address each and every one of these issues. Each one falls under one of four Game Plan principles: 

  • Every Drop: Adapt to the changing climate and limited resources to make the parks system more resilient and environmentally sustainable.
  • Every Person: Ensure equity in the distribution of parks and park resources and programming so that all residents have the opportunity to improve their personal health and well-being.
  • Every Dollar: Manage resources to ensure long-term economic and operational health of the parks system.
  • Uniquely Denver: Provide parks and programming that reflect Denver’s community and cultural identity.

As it relates to our urban forest, our goals are even more specific and there are ways you can help!

Blueprint Denver

Working in conjunction with the Game Plan, Blueprint Denver is a citywide land use and transportation plan for the next 20 years that calls for growing an inclusive city through three basic ideals:

  • Complete Neighborhoods: Creating complete neighborhoods and complete networks everywhere in our city, to meet the needs of all Denverites.
  • Growth Strategy: A measured, common-sense approach to where growth should take place and how it should fit in.
  • Equity: For the first time, considering social equity factors so we can tailor solutions to each neighborhood’s unique needs — ensuring changes will benefit everyone.

Once again, lofty goals, right? Well, we have another 20-year plan that we believe will get us there, with these elements at its heart:

  • Land Use & Build Form: Continue to build the character and quality of places in neighborhoods.
  • Mobility: Connect people to the neighborhood places where they live, work and play.
  • Quality-of-Life Infrastructure: Provide neighborhoods with natural features, active recreation opportunities and social spaces.

At City Forestry, we’re particularly passionate about Quality-of-Life Infrastructure, and we’ve got specific plans to develop and strengthen it. And once again, you can help!

Long story short, Denver has big goals. With your help, the Denveright process will lead us down a path to accomplishing each and every one of them.