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The term native is increasingly being used in horticulture and tree planting practices, but what does it mean and how does it impact Denver’s urban forest? The term native refers to plants that have historically existed in an area and sometimes goes further to only include plants that existed prior to European colonization of North America. The term non-native means plants that have been introduced through human activities. Non-native plants can become naturalized through establishing and reproducing on their own in the new environment. These plants are typically not harmful to the surrounding ecosystem; however, some species can become invasive and cause environmental or economic harm through rapid spreading.

 

 

 

 

 

 

 

 

Native plants are important to local ecosystems because they are well-adapted to the soils and water availability of the area, support wildlife and pollinators and participate in symbiotic relationships and increased biodiversity. Denver is known for its semi-arid, high-plains climate and, prior to tree planting projects, was characterized by cottonwoods and willows growing near streams. Because Denver does not historically have many trees and the trees that are native are not well-suited for urban spaces, the way we plan for the urban forest today relies on non-native species.

Denver sees extreme temperature swings, periods of limited water availability and weather events such as hail and snowstorms, making it a challenging place to grow and establish trees. Through our free tree planting program, we have focused on selecting species that are hardy, add diversity to the urban environment and are resistant to local pest and disease issues. Over the years, the mindset of planting the same species in lines along streets and blocks has shifted to prevent major tree loss events such as the effects of emerald ash borer reaching Boulder in 2013.

To view Denver’s rules and regulations for tree planting within the City right-of-way, as well as the 2025 Approved Street Tree List, please visit our website at denvergov.org/forestry.

In 2024, we planted over 80 different species and cultivars of trees which will support a healthy urban forest for future years. While native trees and plants are important to maintain in our city, selecting a tree for your property or plants for your yard both rely on planting the right species in the right place. This selection process will vary based on your individual site characteristics but will continue to change with differing weather patterns and temperatures to come. Continued research and understanding of available species, as well as development of new cultivars, will help aid in decision making and creation of climate tolerant trees.

For Additional Resources, Visit the Links Below:

Rollinger Tree Collection

CSU Extension Native Trees for Colorado Landscapes

USU Extension Native Tree Discussion

You may be familiar with the program formerly referred to as “Ash GAP Removal and Replacement,” which was started in 2020 to address a “gap” in our response to the invasive Emerald Ash Borer (EAB). The program removes small ash trees in poor condition to reduce host material for EAB. This program, along with our Be a Smart Ash Planting Program and Be a Smart Ash Treatment Program, aims to lessen the damage caused by EAB when it eventually reaches Denver.

In 2024, we refreshed the GAP program name to Ash Removal & Replacement and updated the process of accepting applications and scheduling removals. The no-cost program targets small, poor condition ash trees in the public right-of-way within the City and County of Denver and accepts applications year-round.

To improve the efficiency and timeliness of assessing ash trees and scheduling removals, beginning in 2024, the program will alternate between west and east Denver annually. In 2024, we will operate the program in west Denver, and in 2025, we will focus on east Denver. Moving forward, removals in west Denver will occur during even years and removals in east Denver will occur during odd years.

EAB has been confirmed in multiple front range Colorado cities but has not yet been identified in Denver. We hope our proactive efforts in Denver reduce EAB’s impact on our urban forest. To learn more about the Ash Removal & Replacement program and eligibility requirements, please visit our page here: https://beasmartash.org/ashreplacement/. If you have questions about the program or a forestry-related issue, contact us at Tree@denvergov.org or 720.913.0651.

Between life, work and home, we’re all busy bees these days. It seems like there is always one more thing on our never-ending list of to-dos. But when it comes to your home garden, we want to share an idea from Denver’s Office of the City Forester that will help keep your scene serene. Because keeping things pristine? That takes too much time. So, give yourself a rest and leave a little mess!

Think about the pollinators.

Flowers, fruits and leaves are great for pollinators. Having plenty of flowers and flowering trees around for pollinators is crucial to healthy pollinator populations, which are necessary for food production that we need as humans. It’s all connected.

Flowers, fruit and leaves are also good food sources and habitats for our insects and wildlife. Plus, embracing the messier side of landscaping is vital to maintaining a healthy urban ecosystem, because it helps to balance diseases and pests.

Some trees attract bees.

In 2022 we planted this linden tree on request, as the property owner had a beehive and wanted them to have linden flowers to make their honey.

Leave some leaves.

Collecting leaves is a rite of fall. Raked piles make the cutest landing pads for our little ones and the colors somehow make the chore seem less like work and more like a nice way to get some cool crisp air in your lungs and not feel like you’re actually getting exercise too! But just say no to plastic and instead, responsibly dispose of leaves in compostable paper bags. You can get them for free from our LeafDrop program.

But don’t work too hard – try to leave a few leaves behind. Do a pass or two with your electric mower to chop up the leaves into small pieces for faster return of organic matter into the soil Creating compost from your organic food scraps and yard waste, like leaves, is a great way to make fuel for your trees, lawn and flower beds. Just add a little in when refreshing your mulch.

Besides leaves, how else do trees make an embraceable mess?

Some trees make their mess by dropping seeds, so they can adapt and reproduce the next generation. This post from our friends across the pond tells us about the five ways trees spread their seeds: the plant disperses them by gravity or force, or they spread seeds with a little help from animals, wind or water. Cleaning up after these trees hampers their hard work to survive.

As always, if you need more information, please contact Denver’s Office of the City Forester at forestry@denvergov.org or 720-913-0651.

 

Denver Parks & Recreation has worked with nearly 20,000 volunteers across recreation and urban & mountain parks, this year alone. By partnering with dozens of local and state-wide programs, DPR is fostering current and future generations of environmental stewards. If you have a passion for the outdoors, get involved building a more resilient future today.

Regardless of what the thermometer reads, it appears that summer is coming to an end –– which means that fall will soon bring us the gift of cooler breezes, colorful leaves, and the desire to engage in all the cozy things. It’s a beautiful season to get outside in Colorado, and the perfect time to plant a tree and contribute to our urban canopy.

Fall is a great time to plant new trees!

People tend to think of spring as the time to plant trees, but the truth is, fall can be even better! The heat of summer has left behind healthy soil, ready for planting. And there are plenty of sunny days between now and the first freeze to get those roots growing strong. There is always more to learn, but we’ve narrowed it down to some of the basics here: Everything You Need to Know About Planting a New Tree.

Where should I plant my tree?

Make sure there’s room for a new tree in your public right-of-way, especially if you’re applying for a free tree. We recommend following these spacing guidelines whether you’re applying for a free tree or planting on private property. Basic where-to-plant guidelines:

• 30 feet from the outside edge of intersecting curbs, to preserve the sight triangle
• 35 feet from large shade trees
• 25 feet from ornamental trees
• 20 feet from streetlights
• 20 feet from stop signs
• 10 feet from edge of alleys, driveways and fire hydrants
• 7 feet behind attached sidewalks
• 5 feet minimum from buried electric lines and plant ornamental trees under overhead power lines
• 5 feet minimum from water meters/pits, gas lines[MJPDCM2] , but 10’ preferred
• Centered within tree lawns/planters

How mu(l)ch is too mu(l)ch?

Applying mulch around the tree before it settles in for its winter’s nap is a very good idea. A mulch ring around your tree holds moisture in and protects against temperature extremes. It also decomposes and adds nutrients to the soil, too. We recommend learning the right way to mulch before getting started.

Fall Color 101

While the name Colorado technically means “colored red,” Denver’s variable fall weather makes it tough for that to ring true in our urban canopy. Sure, we have trees that could turn red in fall, but they don’t! The reason why? Red fall color relies on certain environmental conditions, such as a gradual change in temperature…and we all know those early snows in fall feel far from gradual. Plus, many of our favorite and recommended species tend towards yellow or brown fall colors, as these trees can handle the rapid temperature and weather changes we experience.

Tips for trees in cooler months:

Successful fall planting is a critical combination of good timing, a healthy tree and a simple care plan. Following these three tips, your trees will take root in no time.

1. Good Timing – The best time to plant your fall tree is generally through October, but at minimum when nighttime temperatures are consistently above freezing. Planting a dormant tree can ensure that all the tree’s energy goes to establishing, so your tree will be well-rooted by spring.
2. The Right Tree – From the Kentucky Coffee Tree to the Turkish Filbert, there are many trees that thrive in Denver’s climate, each lending its own beauty to our important urban forest. Tree diversity is the healthiest way to combat future pests and disease in our urban forest.
3. Quality Care – Trees are dormant in the winter, but they still need you to keep them watered because the roots continue to grow even with what you see above ground appears to be taking its long winter’s nap. Contrary to what we’ve been told, snowmelt isn’t enough. Trees need care and watering year-round, especially in Denver’s arid climate. Just how much water is determined by the tree’s diameter. The formula is simple: 10 gallons of water for every inch of diameter of tree, with the frequency changing seasonally. (So for a 2-inch diameter tree, you need to water with 20 gallons 1-2 times a month in the winter, and more often during periods of drought (yes, we can get droughts in the winter!) Also, don’t forget to mulch, and watch for sun scald, too!

So, if you plan to plant new trees, you can use the fall season to get them going. It’s easier than you think! But if you need additional help getting going, here are some resources to find a tree care professional in Colorado.

As always, if you need more information, please contact Denver’s Office of the City Forester at forestry@denvergov.org or 720-913-0651.

Dutch elm disease is a fungal disease vectored in part by the elm bark beetle or spread through overlapping roots among elm trees. The disease is known to be lethal to elm trees, and it can rapidly infect neighboring trees of the same species. This disease was first discovered in the U.S. nearly a century ago – brought to the U.S. in European wood that was imported for fine furniture-making. It continues to threaten our elm trees today. Dutch elm disease is essentially incurable, so the best course of action is a hefty combination of diligence and prevention.

A term that may be new to readers is vector which comes from the Latin, vehere – which means “to carry.” Think about it like this: a vector is a bug that carries disease to people and animals. For example, consider how mosquitos and ticks spread diseases that can harm humans and pets. A beetle vector is a beetle that transmits disease, but to plants and trees. Elm bark beetles are referred to as beetle vectors of elm trees. They feast under the elm tree bark, which then spreads fungus into the tree’s “veins,” making the tree very sick and rapid decline soon follows.

These infections are worse when they take root in early spring, when the wood is still moist. But it’s still destructive in the summer. Either way, without early preventative mitigation, the tree dies.

When the tree becomes infected, the leaves in the high branches – or crown – begin to yellow and wilt.  Quickly, the leaves turn brown, curl up and then the entire branch dies. Branch by branch, the disease spreads until the entire tree dies. The American Phytopathological Society (APS) shares this simple-to-understand illustration on the cycle of Dutch elm disease:

Sadly, if you’ve already identified the disease, it may be too late for the tree. But there are still some steps you can take to keep the fungus from spreading.

Like most tree ailments, it’s better to prevent the arrival of an illness than to cure a diseased tree. Prevention involves following good cultural practices, such as not planting too many of the same species of tree in a row, proper watering, avoiding damage to the tree, mulching, and rotational pruning. Property owners should not attempt to diagnose, prune or remove elms that may be infected, as that may unintentionally spread the disease due to beetle or fungus existing in the debris. It’s always best to have a licensed tree contractor perform tree work and remove all debris.

If Denver residents rally to prevent the spread and save the elms, we’ll see success. Below are a few photos of a local tree with Dutch elm disease at the crown. Look familiar? If you see one in a public right of way, please call 720-913-0651 or email forestry@denvergov.org.

 

In the spring of 2023, Denver Parks and Recreation and the Office of the City Forester conducted a comprehensive community-wide survey to gather insights from residents regarding their priorities concerning trees and the urban forest across town. This valuable information is currently being utilized to craft the city’s inaugural Urban Forest Strategic Plan. The plan encompasses all trees within the city, whether on public or private property, and aims to enhance existing goals, introduce new ones, and establish a shared and fair vision for the future of the urban forest.

Trees provide numerous benefits, such as purifying the air we breathe, mitigating the heat island effect, and reducing noise pollution. They offer a welcoming environment for outdoor activities, contributing to better physical and mental well-being for residents. Moreover, a thriving urban forest enhances property values, fosters a sense of community pride, and attracts visitors, boosting the local economy. By caring for and investing in our urban forest, residents can actively contribute to a greener, healthier, and more sustainable city for generations to come.

Building on the knowledge gained from the spring survey, we now have a few additional crucial questions to ask. Your input will continue to play a vital role in shaping the plan, and we highly value your participation. Complete survey #2 by September 4, 2023.

With more people relocating to Denver, warming weather and more frequent periods of drought – we are tapping into our most precious resource like never before. Currently, about 40 percent of water in Denver is used for outdoor landscapes but water isn’t an unlimited resource. That’s why Denver Parks & Recreation has a plan for water efficiency, reuse and response.

Trees are a critical component in the resiliency and health of a city, and also for those who call that city “home.” Whether it’s lending charm to a shady street, shielding people and plants in the parks from the summer sun, or even stepping up to fight climate change, we really do count on Denver’s trees.

But did you know we also count them? There are more than 338,000 trees being tracked in the Treekeeper inventory kept by the Office of the City Forester today. This is a huge undertaking, and partly why we count on residents like you to help keep Denver’s trees growing strong.

From looking out for destructive pests, to learning to identify disease, to assessing and reporting structural damage, there are a few simple steps you can take to keep any tree problems from – ahem – branching out and taking root.

“The earlier we hear about a tree in need, the better. This is why having residents keep an eye out is so important. We couldn’t do this without dedicated residents who care about the urban canopy,” said Mike Swanson, Denver’s City Forester.

What the Pros Know

When Denver’s urban foresters are out surveying the city’s trees, we take a few first steps to assess overall conditions. We’re sharing some of these steps with you. A simple first-pass visual survey might include your asking questions such as:

– Does the tree look like you think it should?

– Does the tree show signs/symptoms of pests? Look out for holes in the trunk, branches, or leaves, defoliation, or oozing.

– Are there structural defects or damage? Look out for broken branches, trunk wounds, or branches lacking leaves

– Is there enough mulch?

– Is there yellowing/browning or even curling leaves in young trees?

– Is there progressive browning at the tips of branches downward, known as dieback?

If you still have concerns, you can dig a little deeper:

– Check the branch for flexibility, the hallmark of a healthy tree.

– Do a scratch test by taking your thumbnail to a young branch to see if it reveals green beneath – if it does, that tree is still living.

– Look out for common bacterial diseases, such as fire blight in fruit trees, which may present as dead branches, water-soaked blossoms and dried-up fruits.

When to Seek Help

With newly planted trees, it’s important to keep an eye on any changes that seem out of the norm. During the growing season, it’s easy to tell because leaves won’t be doing well. You may see abnormal growth such as larger or smaller than normal leaves, yellowing or browning, curling, or even no leaves. To help determine if your free tree needs attention, the quickest way to get help is to email us at tree@denvergov.org.

For larger trees, it may need to be brought to the attention of city forestry inspectors, especially when it’s obstructing important things like street signage or stoplights. Do you see hanging broken branches? Report the tree to 3-1-1 and issue will be routed to an inspector.

Trees are resilient. They can physically compartmentalize a lot of their bumps and bruises and heal many of their own wounds. But some issues can be difficult to bounce back from. This is why your best bet is to prevent damage before an incident harms the tree beyond repair. Most importantly, call a licensed tree-care professional if you need help, to increase the chances of a good outcome.

By keeping a watchful eye on Denver’s tree health, you’re taking care of an urban canopy that takes care of us. Together, we can preserve the beauty and benefits of trees…they’re counting on us!