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2022 was a year of dedicated efforts to grow the city’s urban canopy for a more resilient Denver. Here at Denver’s Office of City Forester, we’ve made progress in expanding our urban forest by planting 1,289 new trees.

What else did we do?

We pruned and planted trees in areas of greatest need, removed trees that could cause damage and collected nearly 800 tons of leaves for compost as part of Denver’s LeafDrop program. 

Why are we doing this?

It’s simple – we need trees! And we strive to create a more resilient city through trees—by planting new, protecting those that already exist, clearing the damaged and susceptible to make way for new growth and serving as a resource for residents who want to contribute to our urban canopy, too. Our trees aren’t just lovely to look at, they also cool our air, keep it clean and slow down rain runoff so more water makes its way into the ground, plus a number of other important benefits.

2022 by the numbers:

• 1,289 trees planted
• $681,227 invested in trees, planting and watering
• 420 ash trees removed through the GAP tree removal and replacement plan
• 33 trees pruned and 42 trees removed that pose a risk to public safety through the Forestry Neighborhood Initiative in specific neighborhoods in southwest Denver
• Nearly 800 tons of leaves collected through Denver’s LeafDrop program in partnership with Denver’s Department of Transportation & Infrastructure and Ace Hardware—up 260 tons from last year!

Where were trees planted?

See below for a breakdown by Denver City Council district of where trees were planted in 2022. Denver’s Office of the City Forester works with community partners and researchers to prioritize tree planting in neighborhoods across the city depending on canopy cover and household income.

In 2022, 870 trees (67.5%) were planted in areas of greatest need according to Denver’s Parks and Recreation’s Neighborhood Equity Index.

What’s next in 2023?

This year, we will continue to plant more trees and provide resources to residents on how we can all take care of our urban canopy.

We also want to help you plant a tree! If you have room in the public right-of-way adjacent to your property, you may be eligible to have a free tree planted for you by Denver’s Office of the City Forester. It’s easy to apply online.

Let’s keep working together in 2023 to protect our urban canopy and improve the climate for generations to come. For more information about any of these programs, email forestry@denvergov.org or call Denver’s Office of the City Forester at 720-913-0651.

As we all prepare our homes and gardens for winter, Denver’s Office of the City Forester urges residents to think about the trees and how to keep our urban canopy healthy during its dormant season. And if the leaves are still falling as you’re reading this, don’t forget to grab a rake, gather them up and compost them in paper bags to keep them out of landfills.

Yes, trees are resilient. But we can help them along by taking a few key steps to winterize them, so they stay healthier year-round. Below are some simple tips, along with links to additional information, to make winter a wonderland for our urban canopy.

WINTER IS COMING

Get the most out of your irrigation system before it takes its well-earned seasonal hiatus. If you’re not winterizing the system yourself, contact your local landscape company now to get on their schedule before freezing weather sets in. But first, remember to get your trees watered and mulched prior to shutting off the system.

TOO MU(L)CH IS NEVER ENOUGH!

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

Ever hear of a mulch volcano? Piling mulch too high around the base of the tree keeps oxygen out, and can be deadly. Keep your mulch ring at least 6 inches away from the bark of the tree.

Vertical mulching is a modern method that also improves soil conditions and allows for deeper water penetration. Vertical mulching removes columns of poor-quality soil around the tree, vertically, and then fills those columns with compost. Learn more about general tree care tips, including mulch.

Bark on the southern/southwestern face of your trees is subject to a condition called sun scald. To avoid this, you can wrap your tree’s trunk using materials like butcher paper, it’s waterproof and removes/absorbs some of the energy that the sun produces. A good rule of thumb is to install tree wrap around Thanksgiving and remove it around Easter.

WINTER NUTRITION TIPS

Remember: dormant doesn’t mean dead, so feeding and watering trees during this season can help them spring back into action in the next. It’s also wise to mow/mulch some of your tree leaves back into the turf to ensure the nutrients are making their way back to nature.

But when it’s 40 degrees or warmer – which is seen a lot during Denver winter – your tree still needs water, and snowfall just isn’t enough. So learn how to water trees in winter and make a plan to stay on top of it. Your “buds” will thank you in the spring.

WINTER PRUNING

Would you be surprised to learn that winter is a good time to prune? Well, put on your parka because certain trees, including American elm and fruit trees in the rose family should only be pruned while dormant to reduce the spread of disease.

If you are pruning something you can’t reach from the ground, it’s advised that you hire a tree care professional since they use specialized equipment and have training and expertise. In the City of Denver, tree contractors are required to be licensed and insured, and Denver has a list of licensed tree contractors for your convenience.

Learn more about watering, fertilization and protecting your trees with these frequently asked questions of winter tree care and give your trees a chance to thrive this season.

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

2022 has been a hot one. But the good news is, autumn is nearly here and soon the air will be crisp, sweaters will take over for t-shirts and your trees’ leaves will start to turn. Which then means your trees’ leaves will also begin to fall.  

Do you have a plan? This “almost there” season is the perfect time to think ahead about what to do with your leaves. Luckily, Denver’s LeafDrop program is here to help, giving Denver residents an easy and free way to take care of their neighborhood and city.    

Here are three easy ways you can turn your leaves into something helpful and keep them out of landfills.  

1. CLAIM YOUR BAGS. Before raking up your leaves, use this coupon to pick up a pack of  free compostable paper bags specifically for leaf collection. Free 5-packs of paper leaf bags are available at participating Denver-area Ace Hardware stores.
2. #COMPOSTINGCOLORS. While you’re raking up leaves, be sure to capture the beauty – and the bounty – of Denver in autumn by snapping a photo of your trees, leaves and LeafDrop bags. Learn how to participate in this year’s fall photo contest and use the hashtag #compostingcolors to be entered to win great prizes.
3. DROP IT LIKE IT’S HOT. Keep your raked leaves out of the landfill and compost them for free through Denver’s LeafDrop program. Weekday sites will open to Denver residents Oct. 10. Weekend drop-off sites will open Nov. 4. Remember, when dropping off your raked leaves, if you’re not using these compostable bags, use paper bags – they can be composted along with the leaves!

Try as we might to keep them well and reaching for the sky, sometimes we simply have no choice but to say goodbye to our strong, shady friends. Simply put, trees don’t live forever. And tree removal – while sad to see – is an expected part of the natural lifecycle. The “whys” of tree removal can vary greatly, but there are some rules that stand firm. One thing you’ll hear our foresters say often is “right tree, right place”. This simple reminder also serves as a starting point for the list of reasons a tree might need to be removed. Here are the top five reasons:  

1. Right tree, wrong place.

This one breaks many hearts because, well, it didn’t have to end this way. Planting a good tree in a bad spot generally stems from a lack of understanding or planning on the part of the OP, or original planter. Reasons here can range from HOA regulations that don’t allow planting in certain areas, to some city regulations that don’t allow certain types of trees to be planted under overhead power lines or in certain rights-of-way. The best way to avoid this is to research in advance what’s allowed and where. For example, you should never plant a tree within 20 feet of a stop sign, 10 feet from a fire hydrant or five feet from water meters. And dial 8-1-1, it’s required prior to planting. 

2. Wrong tree, right place.  

Even if you have the perfect location for a tree that meets all the requirements outlined above, there are still some trees that aren’t permitted due to structural issues, overplanting or threats of invading insects. The most common trees planted without permits are silver maple, autumn blaze maple, aspen, cottonwood, evergreens and of course the ash tree, which we know is at the greatest risk for invasion by the emerald ash borer.  

3. Wrong tree, wrong place.   

This is when everything’s, well, wrong. A small spruce tree planted along the street near the corner may not be a concern now, but as the tree grows it’s likely to create a visibility obstruction for drivers and pedestrians. It may also shade the sidewalk and/or street, delaying the melting of snow and ice, which may create dangerous conditions for the public utilizing the public right-of-way. In this case, it’s best to remove the tree while it’s small and before it becomes a safety concern.  

4. Diseased or dead.  

Health and safety of a tree isn’t always apparent to the naked eye. What may look lush and lively at first glance, might turn out to be hollow or otherwise sick, leaving passers-by, property and neighboring trees at risk. Learn how to tell if your young tree is diseased, dead or just dormant. For larger trees it’s probably best to contact a certified arborist to do a health evaluation. 

5. Someone didn’t tree-t ‘em right.…and you thought we didn’t have any tree puns left! 

We already know it – prevention is the best medicine. Infestations may spread to neighboring trees so removal may be necessary to prevent an infestation from impacting adjacent trees. If you currently have the right tree in the right place, we can’t stress enough that you should do whatever you can to keep it well for a long healthy life. That includes regular pruning and care and working with a professional arborist when needed.  

The primary job of Denver’s Office of the City Forester is to attempt to preserve every tree we can, while also following these rules. If you see us removing a tree, it’s generally for one of the above reasons.  If you think a tree is being wrongly removed, let us know by contacting our office at 720-913-0651. 

Hey, we get it – it’s easy to think “the more the merrier” when it comes to trees. But planting any tree in the public right-of-way (areas between the curb and sidewalk or next to the street), isn’t always good for the future of our urban canopy.  

In fact, some trees can be problematic there. The silver maple is one of those trees. As they mature, these trees become tricksters because they tend to decay from the inside out. Imagine if you will, a tree that’s 30” in diameter, looks great – with lots of leaves – but is hollow inside. Now imagine that tree over the sidewalk or the curb, and the harm it could bring if it were to fall. But the silver maple isn’t the only species facing challenges in Colorado. Read on to learn more about approved street trees, unpermitted street trees and those that fall somewhere in-between.  

Get planting!  

The approved street tree list for Denver’s public rights-of-way includes trees that, when given proper and consistent maintenance, including supplemental irrigation, proper pruning and mulching, will be assets to Denver’s urban canopy because of their ability to thrive in our climate. Trees not included on this list may not be planted in the public right-of-way (as a street tree) without express permission from the Office of the City Forester. Here are a couple tips to help you plant it right:  

• When possible, obtain trees that have been grown from a local seed source. Locally grown trees will be adapted to our area’s highly variable, and often harsh, growing conditions.  
• If locally grown trees cannot be obtained, source from locales that have similar growing conditions to our area (precipitation, soil pH, high/low temperatures, etc.)  
• Review these basic tips about planting a new tree.  
• Email forestry@denvergov.org to get your free tree-planting permit! 

Right-of-way? More like wrong-of-way.

Most of the trees listed below tend to develop structural issues. Others create obstructions in various ways. All of them are not welcome in the right-of-way. Per Denver Forestry Rules and Regulations, the following trees may not be planted in the public right-of-way:  

• Any of the poplar (Populus) species including cottonwoods and aspens  
• Any of the willow (Salix) species  
• Boxelder (Acer negundo)  
• Siberian elm (Ulmus pumila)  
• Multi-stemmed trees  
• Weeping and pendulous trees   
• Evergreens  

Hit pause on these . . . for now.

Other trees – for reasons such as insects, overplanting, invasiveness or structural issues – are currently under a moratorium for planting in the public right-of-way, including:  

• Ash (Fraxinus) species, due to the threat of emerald ash borer (EAB)  
• Walnut (Juglans) species  
• Silver maple (Acer saccharinum)  
• Autumn Blaze / Freeman maple (Acer x freemannii)  
• Sunburst honeylocust (Gleditsia triacanthos inermis ‘Sunburst’)  
• Bradford pear (Pyrus calleryana ‘Bradford’)  
• Mulberry (Morus) species  
• Russian-olive (Elaeagnus angustifolia) 
• Tree-of-heaven (Ailanthus altissima), invasive, structural issues and due to the threat of the spotted lanternfly 

If you see a tree excluded from the above list, it may be permitted on a case-by-case basis. Contact the Office of the City Forester at forestry@denvergov.org or 720-913-0651 for details, site inspections and planting permits. As always, we depend on the eyes and ears of the tree loving community to keep us informed.  

“I never saw a discontented tree.” ― John Muir 

Trees work hard. From taking the heat to covering the street, from helping our health to growing our wealth, entering a tree-lationship can be good for you – and your city – in more ways than one. So, if you take care of your trees, they’ll really take care of you! 

Here are eight research-backed ways to prove that trees are excellent neighbors.  

1. They fight crime. Research₁ indicates that a 10% increase in tree canopy can be associated with a roughly 12% decrease in crimes such as robbery, burglary, theft and shootings. 

2. They keep us cool. Trees can cool cities by up to 10 degrees, fighting off the heat island effect and preventing heat-related illnesses in urban areas like Denver. This comes from cooling and evaporation,₂ not just shade.  

3. They save us money. Trees properly placed around buildings can reduce air conditioning needs up to 30% and can save 20–50% in energy used for heating. By providing protection from the sun and wind, trees can reduce energy costs by as much as 30%. Urban tree cover supplies heat-reduction services worth $5.3–12.1 billion annually.₃ 

4. They might make us feel better. Research has shown that spending time around trees and nature can reduce depression and anxiety. One study₄ suggests that unintentional daily contact with nature through street trees close to the home may reduce the risk of depression, especially for individuals in under-resourced communities. 

5. They help us breathe. One large tree can provide a day’s supply of oxygen for up to four people!  

6. They keep us healthy. In some cases, just seeing trees does the trick! Often cited as one of the earliest studies₅ of the possible relationship between access to greenspace and health: surgery patients with windows overlooking natural views had shorter postoperative hospital stays!  

7. They even clean our air! In one year, an acre of mature trees absorbs the amount of CO₂ produced by a car driven 26,000 miles.  

8. They can make us money. Every dollar spent planting and caring for a community tree, yields benefits that are 2X to 5X that investment! Healthy trees can boost your property’s value by 5 to 20%.  

 Because as the Lorax, who spoke for the trees, once said, “Unless someone like you cares a whole awful lot, nothing’s going to get better. It’s not.”  

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1. Troy et al. 2012   
2. Rahman et al. 2020 
3. McDonald et al. 2020 
4. Marselle et al. 2020 
5. Ulrich 1984 

Other resources:  

• U.S. Forest Service: https://www.fs.fed.us/psw/news/2011/110308_arborday.shtml     
• National Arbor Day Foundation: https://www.arborday.org/trees/treefacts/     
• Colorado State University Extension: https://csfs.colostate.edu/colorado-trees/     

Trees are our first line of defense when it comes to combatting the urban phenomenon of the Heat Island. No, Heat Island isn’t a new reality show. Although it is a reality.  

What is a Heat Island? 

The easy explanation by NASA’s Climate Kids is that an urban heat island occurs when a city experiences much warmer temperatures than nearby rural areas. The difference in temperature between urban and less-developed rural areas has to do with how well the surfaces in each environment absorb and hold heat. Cities tend to have more impervious surfaces, such as buildings, sidewalks, roads and patios, which hold more heat.  

Cities throughout the world are experiencing urban heat islands, and Denver is no different. Take a look at Denver’s Heat Island map:

This map uses impervious surfaces as a proxy for heat. In this map, the darker colors represent hotter areas 

…and now take a look at the map of the city’s trees:  

In this map, the darker the color, the higher percentage of tree canopy cover there is. 

See how they are essentially opposites of each other? Meaning, the places with lower heat vulnerability are also the places with the highest tree canopy coverage. It’s clear to see that trees make a difference.  

Now that we know it’s this easy, what can we do? You guessed it.  

Plant. More. Trees.   

Now you may be asking, what is it about trees? It can’t just be the shade they offer. What else is taking place? It’s a great question with only a halfway-surprising answer. Because a lot of it does have to do with the shade they provide and the sunlight they deflect. But there is also something else happening that helps trees cool their surrounding area… 

Evapotranspiration.  

Over at USGS.gov (United States Geological Survey), a science bureau within the United States Department of the Interior, there is a simple illustration that says it all: Evapotranspiration simply describes how water working through the tree ends up cooling the air around it. Water (precipitation) comes in through the roots and is released as vapor (transpiration). And, as an added bonus, the soil releases even more water to cool the air down low (evaporation).

So, one of the best ways we can combat heat islands is by planting more trees. Two ways you can do that: apply for a free tree in your public right-of-way and plant more trees downtown.  

All of the above combined results in a drop in temps and a happier, healthier – and much cooler –community. If you’ve read all the way through and you still want to learn more, check out this PBS interview from 2021, featuring Denver’s own City Forester Mike Swanson talking about Heat Islands.   

If water is life, then mulch is a lifesaver! When we talk about tree care in the summertime, we are mostly talking about the one-two punch of watering and mulching. Below you’ll find a round-up of some simple tips for summertime tree care.  

BE WATER-WISE 

Before you start watering, make a plan based on the trees you have. Answering these questions can help you make a watering plan that works. 

• How old are your trees?  
• How much water will they need?  
• How do you tell if you’ve watered enough?  
• When should you water?  
• When should you not?  

How can I check if my tree needs to be watered?  

Easy! Feel it with your hand. Dig down into the soil a few inches and squeeze with your hand to feel if it is wet, dry or somewhere in-between.  

How much water do I use?  

If your tree is young and still establishing, it will need a little more TLC, so shoot for 15-20 gallons, every 2-3 days. After your tree becomes established (it usually takes a two-inch caliper tree 2-3 years to establish), you can reduce the watering frequency. However, we still recommend following the 10 gallons of water per inch caliper of the tree, watering when we experience long periods without precipitation and throughout the winter. Allow soil to dry between waterings and continue to monitor your soil moisture to determine when your tree needs to be watered.  

How can I make sure water reaches deeper into the soil? 

A simple hose is the most basic tool needed to water your tree, but soaker hoses, soft spray nozzles and soil needles can help break through the soil surface. Most absorbing tree roots are found in the first 12-inches of soil depth; apply water slowly so it has time to absorb into the soil and reach these vital roots.    

How can I tell how much water my tree is getting through my hose or irrigation system? 

You can determine your hose’s output by taking a container of known quantity, like a gallon jug or five-gallon bucket, and setting a timer for how long it takes the hose to fill up the container at a trickle. Then you can calculate how long you should trickle your hose to achieve a certain quantity of watering. Irrigation systems themselves generally do not provide enough water for young trees during their establishment phase, so plan on giving supplemental water as well and checking the soil moisture regularly.  

What else?  

As travel begins to pick back up and Denver residents start hitting the road, don’t forget to make a tree care plan while you’re gone. When possible, ask a neighbor, family member or friend if they’ll water for you and you can offer to do the same for them. And remember to check with your utility department for preferred times, right-day usage and other potential temporary changes.   

MULCH-MUSTS 

Mulch: it does so much! Keeping a mulch ring around young trees keeps them safe from mower and string trimmer damage, which can be an easy point of entry for pests and disease. It also holds moisture in and protects against temperature extremes. It decomposes and adds nutrients to the soil, too! 

Here’s how it’s done:  

Apply wood chips, bark, or other organic mulch 2 to 4 inches deep in a ring around the base of the tree, but at least 3 inches away from its trunk. Mulch reduces soil evaporation, improves water absorption, insulates against temperature extremes and can break down over time, adding necessary nutrients to the soil. Make sure to replenish your mulch as necessary, at least a few times a year.  

We said MULCH, not rocks or grass.  

Rocks as “mulch” are bad for trees. They retain heat, causing the soil temperature to rise and that increases evaporation. Plus, rocks don’t provide essential nutrients and can actually change the soil chemistry, which can be unfavorable for many trees. They’re not all bad, though – rocks and xeriscape lawns can be a way to conserve water in other areas of your garden, but it is essential that the area with your tree roots is covered with mulch or other organic material.  

For different reasons, grass around the base of the trunk is also not recommended. Why? Because grass is greedy. It competes with young trees for moisture and nutrients in an already water-scarce climate. Plus, having grass close to your tree increases the risk of mechanical damage to the trunk from lawn mowers or string trimmers.  

Vertical Mulching 

For those of you ready to graduate from Mulch 101 and really dig into the topic, we present vertical mulching. Vertical mulching can alleviate soil compaction, which jeopardizes tree health and is commonly found in Denver in areas with clay soil or recent construction. Vertical mulching improves soil conditions and allows for deeper water penetration. Yep – it’s all related. It’s accomplished by removing columns of poor-quality soil around the tree in a radial or grid pattern, and then filling those columns with compost. You can watch this video for more information.  

TREE VITALITY = EARTH VITALITY  

We hope that all these tips help you determine how much water each of your trees need, what type of mulch to use and why it all matters. Because when done correctly, these steps can increase tree vitality, which can help your trees stay healthy year-round and keep our urban canopy in great shape for the future. 

We interrupt our regularly scheduled how-to blog posts to bring you information about two tree-riffic events happening in Denver later this week: The International Society of Arboriculture’s Rocky Mountain Chapter Tree Climbing Competition and Earth Day Remastered.  

The Be A Smart Ash team will have a booth at both events, so we hope you stop by and say “hi”. And don’t worry, we’ll have plenty of how-to information on hand.   

The International Society of Arboriculture’s Rocky Mountain Chapter Tree Climbing Competition  

When: June 24-26, 2022  

Where: City of Nairobi Park, 3500 Cook St., Denver, CO 80205 

What: The International Society of Arboriculture’s (ISA) Rocky Mountain Chapter Tree Climbing Competition is happening this weekend, and it’s just what it sounds like. But it’s not for kiddos – this one’s for the pros. Working arborists in the Rocky Mountain region from Colorado, New Mexico, Wyoming and Montana will be demonstrating climbs, and exchanging ideas for new techniques and equipment, as well as best practices for safe work, all in an atmosphere of friendly competition.  

From The International Society of Arboriculture’s website:  

Professional tree climbing competitions are held around the world to provide a platform for arborists to learn about the latest in climbing techniques and innovations in equipment. They showcase the highest level of professional skills and safety, providing a competitive learning environment for those working in the industry. 

The competitions simulate working conditions of arborists in the field. Male and female competitors perform five different events during preliminary rounds. Each event tests a competitor’s ability to professionally and safely maneuver in a tree while performing work-related tree-care tasks in a timely manner. 

Competitive tree climbing also introduces the public to the skills professional tree climbing arborists must use for safe, professional tree work. 

View the complete schedule if you want to stop by and watch the action. The winners of this event will go on to represent ISA Rocky Mountain Chapter at the North American Tree Climbing Championship as well as the annual International Tree Climbing Championship. 

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Earth Day Remastered 

Come celebrate our commitment to a healthy planet – it’s free and open to the public!  

When: Sunday, June 26, 12-4 p.m. 

Where: Washington Park, South Meadow near Franklin and Mississippi 

What: Join District 6 Councilman Paul Kashmann and the District 6 team for Earth Day Remastered, a free community event “Celebrating Our Commitment to a Healthy Planet.” The afternoon will feature music, exhibitors displaying products and services to help reduce your carbon footprint and keynote speakers committed to climate action. In addition to Councilman Kashmann, Earth Day Remastered is sponsored by the University of Denver and Love My Air Denver. 

For more information, visit the website.   

Since 1872, this “day” has been a celebration of trees. Its birthplace is Nebraska City, NE, but it took root on both coasts and eventually propagated worldwide. Today, this holiday remains an expression of how we joyfully celebrate the planting of trees. According to the Arbor Day Foundation, Arbor Day is a day for people to come together in recognition of the wonders of trees. Communities, schools, businesses, and individuals alike join together to plant commemorative trees, hand out free trees, provide education on tree planting and care, and celebrate all the benefits trees provide.

Now, this is a holiday we can all get behind!

While it’s 150 years strong – older than most of the trees we see every day – it is surprisingly not always easy to track down this holiday on the calendar. So, when is Arbor Day, anyway? National Arbor Day is the last Friday in April, while here in Colorado, we celebrate Arbor Day on the third Friday in April. But take a look at the map and you’ll see that it changes from state to state.

For example, Arbor Day is celebrated as early as January in Louisiana and in November in Texas… and even as late as December in South Carolina. A quick internet search will tell you that the time to celebrate is flexible, and that is based on the best times to plant trees in that area.

#DenverLovesTress Photo Contest

In May, and in honor of this year-long holiday, we decided to branch out and launch a little social media competition here in Denver. The weekly winners received an Ace Hardware gift certificate, so they could celebrate Arbor Day by planting a tree when it’s convenient for them.

Look at the compilation of photos from fellow tree lovers and you’ll understand why we were stumped by which submissions to choose. It’s pretty tough to take a bad picture of something so rooted in natural beauty. But we managed to be-leaf in ourselves and eventually selected the following winners (and we’re sharing some of the runners-up, as well).

With that, we wish you a Happy Arbor Day, Denver! And remember: The best time to plant a tree may be 20 years ago, but the second-best time is today.

Contest-winning images:

…and while these didn’t make the podium, we still think they’re worth sharing.

Other submissions from the contest: