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Tips and Tricks for Pruning Your Trees

By Urban Forestry Operations Assistant Paul Cancik

With spring upon us, many residents are eagerly planning their gardens and starting to spruce up their yards. Pruning helps trees live longer, which allows them to grow taller and contribute to Denver’s urban canopy. With this in mind, Denver’s Office of the City Forester is offering helpful tips for pruning. It’s important to keep in mind that if you cannot safely prune your tree from the ground, it’s best to hire a licensed tree care professional since they use specialized equipment and have the necessary field knowledge. When you prune a tree, you are planning for the future, and with patience, you will ultimately have results that benefit generations to come.

Why should you prune your trees?

  • Pruning helps ensure that your tree develops a strong form/structure and prevents breakage in the future. 
  • Thinning your tree makes the crown (top) healthier by allowing more air and sunlight to pass through it. 
  • Pruning, much like watering, helps give your tree longevity; future generations will be able to enjoy it.
  • Removing deadwood from your tree helps prevent insect infestation.
  • If pruning is neglected, a tree can become susceptible to breakage, making the tree potentially dangerous.

What should you prune from your trees? 

  • Follow the “3 D’s” of pruning: only remove Dead, Damaged and Diseased wood, especially if the tree is not established. You can also prune branches that impact the structural integrity of the tree. 
  • Be deliberate about what you prune from a tree. 
  • It’s important to prune around stop signs and to ensure sidewalks are clear to prevent accidents on or near your property. Stop signs should be clearly visible and sidewalks free of obstructions. The clearance requirements in Denver are 8’ above sidewalks and 13.5’ above streets and alleys.

When should you prune your trees?

  • While you may prune your tree year-round, ideally the best time to prune is late in the dormant season or early spring, before leaves form. This is typically a good time to remove excess or undesired branches because the tree is not putting forth energy to create foliage.
  • Certain trees, including American elm (Dutch elm disease) and fruit trees in the rose family (fire blight) should only be pruned while dormant to reduce the spread of disease.
  • Only prune a young tree two years after it has been planted and just focus on dead, broken, crossing and interfering branches.  

Tips for pruning:

  • Make sure that every pruning cut you make is clean and smooth. The best tool to use for pruning is a pair of sharp bypass hand pruners for one-inch branches because they make smaller cuts that the tree can recover from faster.
  • Colorado has a very short growing season compared to other regions. A shorter growing season means the tree has a shorter period of time to create and store energy, which ultimately affects how quickly a tree can recover from pruning. A young established tree can tolerate removal of 1/3 of its foliage in a growing season. A mature tree should never have more than 25% of its live foliage removed in one growing season. 
  • If you are pruning something off your tree that you can’t reach from the ground, it’s advised that you hire a tree care professional since they use specialized equipment such as an aerial lift truck/bucket truck and they have the needed field knowledge and expertise. In the City of Denver, tree contractors are required to be licensed and insured. A list of Denver’s licensed tree contractors can be found by visiting
  • If you suspect an insect problem, contact a tree care professional to develop the most effective and environmentally conscious solution. 
  • Covering a wound or using wound dressings is not recommended and may be detrimental to tree health.

Want to learn more? Our friends at The Park People offer a community forester program with classes that cover a variety of topics, including pruning and tree planting basics. You can sign up here:

 Happy pruning!

The Importance of Winter Tree Maintenance

By Michael Swanson, City Forester, Denver Parks and Recreation

As winter approaches, many Denverites are preparing for the cold months ahead by blowing out their sprinkler systems and composting their leaves. But many mistakenly think their trees are self-sufficient and that the snow, when it comes, will provide enough moisture to sustain them until spring. That’s unfortunately not the case. Trees need water year-round, especially in our arid climate.

Here are a few signs that your trees may be in distress and tips for how to winterize your trees to help them stay healthy year-round:

Signs of tree in distress:

  • Trees that exhibit premature autumn color or shed leaves prematurely
  • Advantageous shoot growth along the branches and/or trunk of the tree or near the base of tree
  • Deadwood throughout the crown of the tree

Tips for your trees in winter months:

  • Use 20 gallons of water per week for every inch of diameter of tree (for instance, a 2-inch diameter tree needs 40 gallons of water in a one-week period). A new tree will need focused watering atop the root ball and then throughout the rest of the planting area.
  • Don’t forget that even when it’s 40 degrees or warmer, your tree still requires watering.
  • Apply mulch around the tree, leaving a six-inch gap between the tree trunk and the start of the mulch; mulch should extend by a three-to-four-foot radius from the trunk of the tree or to dripline (whichever comes first).
  • Portions of Southern or Southwestern-facing trees are subject to sun scald. Sun scald is the damage that occurs to living cells just underneath the bark of a tree due to the day-and-night fluctuations during Colorado’s winter months. Signs of damage include discolored and/or cracked bark or sunken areas within the bark. This is a serious byproduct of our warm winter days. To avoid this, you can wrap your tree’s trunk using materials such as cloth or tree wrap available at a hardware store. Butcher paper is a great tool as it’s waterproof and removes/absorbs some of the energy that the sun produces.
  • Keep an eye out for signs of emerald ash borer (EAB), which has destroyed millions of ash trees in the Midwest, has been discovered in Boulder and recently in Arvada and will inevitably arrive in Denver sometime in the near future. There are an estimated 1.45 million ash trees in the Denver metro area, including 330,000 in the City and County of Denver. That means that one in six Denver trees are ash trees, and they can be found everywhere in the Mile High City – with the majority on residential properties.
  • Become familiar with the Be A Smart Ash campaign, which aims to actively educate and enlist the help of you – our City and County of Denver residents – in the process of identifying, treating and replacing ash trees. 
  • Check out this interactive tree inventory map and information about ash tree treatment options and resources to find a tree care professional

Recommended tree care supplies include:

  • Water device (such as a soft spray wand) for winter watering (can also be used year-round)
  • Soil moisture meter (it tells you when the soil is dry and needs water)
  • A hose (make sure it’s the right length to reach your trees if they are a long distance from your spigot)
  • Tree wrap
  • Pruning shears to remove dead wood
  • Gloves
  • Compost comprised of organic food scraps and yard waste (use it on your trees, grass or flower beds when you are refreshing your mulch; when using compost with your trees, do not apply more than a quarter inch per year within the dripline of the tree, and make sure the compost does not come into contact with the trunk of the tree or roots)

Learn more about winter tree care by watching the third episode of Water, Trees, Life.

William Carlos Williams once eloquently wrote: “…having prepared their buds against a sure winter, the wise trees stand sleeping in the cold.” Let’s help our trees prepare for winter slumber so we can enjoy their healthy urban canopy next year and for years to come.


Water, Trees, Life Livestream: Fall Colors & Leaf Bags

Welcome to the Water, Trees, Life livestream!

Grab your family and friends for this interactive, educational show from the Be A Smart Ash team. Each livestream brings the natural world of Denver into the comfort and safety of your living room. The third episode in the series debuted on Friday, October 16 at 11 AM on the Denver Parks & Recreation Facebook page, but you can watch the episode in its entirety above.

In Episode 3, leaf-peeping season is in full swing, and we want to help you enjoy it. We discuss the importance of winter watering for your trees, explore the beautiful fall colors and provide tips about how to protect your ash trees from Emerald Ash Borer. We also explain how you can turn your fall leaves into EcoGro compost, available locally from Ace Hardware. See previous episodes here.

How to Be a Smart Ash | An Inside Look into Denver’s Tree Planting Program

Lexi Brewer, Urban Forestry Operations Assistant, City and County of Denver

As an Operations Assistant of Denver’s Office of the City Forester and a member of the Be a Smart Ash (BASA) team, I have loved being a part of a program that gives away free trees to Denver residents. But a lot of behind-the-scenes work happens to make our streets and neighborhoods green and shaded. In this blog post, I’ll describe our program and how you can help us grow Denver’s urban forest.

Why Plant Trees?

Tree planting is just one part of our BASA program. BASA started in 2016 as a holistic way to stop the spread of Emerald Ash Borer (EAB) by making our urban forest as resilient as possible. The EAB is a non-native insect that targets Ash trees (Fraxinus genus). The larvae of EAB burrow under the bark of the tree, which eventually prevents the tree from being able to transport the necessary nutrients between its leaves and roots for survival, ultimately killing the tree. In Denver, this pest will have devastating consequences, as approximately one in six of all of our trees are ash trees. To reduce and slow the impacts of EAB, our BASA program 1) treats existing ash trees with pesticide, hoping to increase their resistance to EAB, and 2) plants new, diverse trees that will help to fill the holes in the canopy after the death of any ash trees. Planting for diversity will also increase the resistance of our canopy to any potential future pests. Here’s how our planting program works:

Step 1: Spread the word!

Our BASA program is an “opt-in” program, which means that homeowners have to hear about the program and apply either online or with a mail-in postcard. We rely on neighbors and community partners to spread the word about our program and increase the number of people who apply – which will increase the total number of trees that we’re able to plant!

Step 2: Choose where to plant

First, we have to understand which areas of the city could benefit the most from our free tree service. To do this we work with community partners and researchers to create and analyze the data that we need. We prioritize our target planting areas based on lowest canopy cover and lowest annual household income per neighborhood, trying to service first those who could benefit the most from free trees.

In this video, one of our partners, Sylvia Leon Guerrero, discusses the benefits of trees, and how her research used GIS mapping to locate the areas of the city where trees could increase walkability and have other tremendous community benefits.

To determine exactly where we should plant the tree(s) on each property, a member of our staff goes out to the property of the homeowner who made the request. We try to plant as many trees as possible onto a site, being sure to comply with the siting requirements of the city (see below). We also look around and make a species recommendation based on the surrounding trees, trying to increase the species diversity on each street as much as possible. We’ll also note the site conditions in order to recommend a tree that will have the highest chance of survival in the area. We always email the homeowner these recommendations and work with them to provide a species that they like.

Step 3: Plant the tree & ongoing care

After the tree placement and species have been approved by the homeowner, we then use contractors to drop off and plant the trees. From there, our work is done; however, the on-going care of the tree is critical to its survival. We depend on the homeowners to water and care for their tree. Proper watering includes watering with a hose two to three times per week in the summer, at least ten gallons each time (15 to 20 minutes) and two times per week throughout the winter when the soil is dry. We’re happy to answer any care questions that anyone has at With proper care, each tree brings us one step closer to a more beautiful, resilient, urban forest!

Find out if you qualify for a free tree and learn more through exploring our website.

Denver Ash Tree Removal and Replacement

Knowing you Denverites are likely spending more time at home and in your yards than in previous summers, we want to help you learn more about how you can help protect and preserve Denver’s urban canopy and specifically, what the City Forestry team is doing this year to help combat a relentless ash tree insect.

You may be familiar with the Be A Smart Ash program, and you may have heard that the threat of Emerald Ash Borer (EAB) on 1 in 6 of Denver’s trees is imminent. The Q&A below will help explain what the City Forestry team is doing in select neighborhoods to combat EAB; i.e. removing ash trees in poor condition in your right-of-way and how they will replace that tree with a free tree – regardless of whether you have an ash tree – to help bolster and diversify our precious urban canopy. 

Read more

Water, Trees, Life Livestream: Discover Denver’s Urban Forest

Welcome to the Water, Trees, Life livestream!

Grab your family and friends for this interactive, educational show from the Be A Smart Ash team. Each livestream brings the natural world of Denver into the comfort and safety of your living room. The second episode in the series debuted on Friday, July 17 at 11 AM on the Denver Parks & Recreation Facebook page, but you can watch the episode in its entirety above.

In Episode 2, we visited the often-overlooked 14,000 acres of Denver Mountain Parks to explore the relationship between forest ecology and Denver’s drinking water. We then took a trip back down to the city to learn about how we can plant trees to make parks more accessible. Finally, we spoke with a wildlife expert about our urban beaver population — that’s right, Denver has beavers!

Read more

How to Protect and Preserve Denver’s Urban Canopy

Michael Swanson, City Forester, Denver Parks and Recreation, wrote about how his forestry team is taking care of ash trees located on city property (including parks) and in the public right-of-way.

Learn how you can personally contribute to the effort to protect and preserve Denver’s urban canopy here.

Water, Trees, Life

Join the forestry team from Denver Parks and Recreation as they guide us through three stories about the natural world in Denver and a discussion about how we help our urban canopy thrive.

Winterize Your Trees

The new year is in full swing and as the winter weather ebbs and flows, Denver will continue to see freezing temperatures, flurries of precipitation and snowstorms potentially as often as we see sunny, 60-degree days. We caught up with the smart folks at Denver Parks and Recreation’s forestry office to discuss the best methods for winterizing the trees in your yard. For insight and expertise on how to protect your trees from Denver’s highly variable winter months, read on.

How should a homeowner protect a tree during the winter months?
Place mulch around the base of the tree, about three to four inches from dripline to dripline, if not three to four inches. Leave a three-inch gap from the edge of the mulch to the stem of the tree. Because we have warm winter days in Denver, too, watering your tree in the winter is also essential. Flood irrigation around the tree when daytime temperatures reach 45 degrees or higher (if the drip line lacks residual snow cover). In Colorado, winter watering months are typically November to February. Regardless of the age of the tree, this advice applies across the board.

Is there an ideal timeframe that Colorado homeowners should have their trees pruned each year?
Pruning can be done at any time. The dormant season is best for pruning, especially for fruit trees, but homeowners who do their own pruning should wait until they can determine the difference between live and dead material. Always hire a professional if you’re unsure. However, American elms and any tree in the rose family (crabapples, pears, plums, cherry, apple) should be pruned during the winter months. Fruit trees should also be pruned in the winter months to avoid the spread of fire blight. Pruning maple and walnut trees during winter months is not ideal because they will bleed sap from the pruning cuts.

Should people expect a certain level of damage to their trees during the winter or can it be entirely prevented?
Winter damage can be avoided if trees are regularly watered and properly mulched. Damage can occur in what we describe as “heavy load events” – a lot of snow breaking limbs – or a quick hard freeze, especially common for conifer trees. We saw this happen recently in October 2019 because of the two freezing nights.

When discussing winter damage, the term “dieback” comes up fairly often. What is dieback?
Dieback is a condition in a plant in which branches or shoots die from the tip inward; caused by many conditions, but particularly a drought condition if they are not properly watered.

If branches break in a snowstorm, what’s the best use of those that have fallen or broken?
We advise mulching them and re-using that material in your landscaping, flower beds and even around the base of your trees by chipping material using a brush chipper. Alternatively, Denver’s Department of Transportation & Infrastructure (formerly Denver Public Works) collects a limited amount of branches. These must be no larger than four inches in diameter, and they must be cut into lengths of four feet or less, bundled and tied, and weigh no more than 50 pounds. Customers may set out up to 10 bundles of branches on their scheduled every-four-week extra trash collection. Denver residents can also drop off branches at the Cherry Creek Recycling Drop-off center.

Do you have any other tree winterizing tips?
For young trees wrap the trunks each year with tree wrap, until the bark develops furrows. This is especially important with thin-barked species such as honey locust, maple, linden and fruit trees. Starting at the base, wrap the trunk covering each turn about 30% up to the first branch union of the canopy to protect them from the intense sunlight.