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Tree Care & Arborists in Denver, Colorado

Local tree care information, common threats, and certified arborists in Denver, Colorado.

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Tree Care in Denver, Colorado

Every tree in Denver is there because somebody planted and watered it. The Front Range is naturally shortgrass prairie — the city's elms, ashes, maples, honeylocusts, and oaks survive on irrigation and care in a semi-arid climate (Zone 5b/6a) with 8-15 inches of natural precipitation, intense sun at altitude, and temperature swings that can drop 60 degrees in a day.

Ash is the story right now

Roughly one in six urban trees on the Front Range is an ash, and emerald ash borer — confirmed in Boulder in 2013 and since found in the Denver area — makes every one of them a decision. Healthy, well-placed ash can be protected with trunk injections on a 2-3 year cycle; declining ones should come down before they turn brittle. If you have an ash and no plan, that's the first call to make. Denver's forestry office has pushed EAB awareness hard — take advantage of their resources.

Water is tree care here

The biggest killer of Denver trees isn't a bug; it's drought stress — especially winter drought. Dry, warm winter spells desiccate roots, and evergreens keep losing moisture year-round. Water deeply monthly in dry winters (when it's above 40°F and the ground isn't frozen), and deeply-but-infrequently in summer. Frost cracks on thin-barked maples, sunscald on young trunks (wrap them the first few winters), and hail damage round out the local hazard list.

City rules worth knowing

Denver requires tree companies working in the city to be licensed, and trees in the public right-of-way — the strip between sidewalk and street — fall under the City Forester's jurisdiction even though adjacent owners are responsible for their care. Permits are required for planting, pruning, or removing right-of-way trees. Check with Denver's Office of the City Forester before touching a street tree.

Planting for the Front Range

Diversity matters after the ash crisis: bur oak, Kentucky coffeetree, hackberry, honeylocust, catalpa, and Rocky Mountain juniper handle alkaline soils, drought, and cold snaps. Plant in spring here — fall-planted trees face winter desiccation before roots establish.

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Common Tree Threats in Denver

Emerald Ash Borer

Moderate

An invasive wood-boring beetle native to Asia that has killed hundreds of millions of ash trees across North America since its discovery in Michigan in 2002. Larvae feed on the inner bark, disrupting nutrient and water transport.

Insect

Mountain Pine Beetle

Critical

A native bark beetle responsible for massive die-offs of lodgepole, ponderosa, and whitebark pines across western North America. Climate change has expanded its range northward and to higher elevations. Outbreaks have affected tens of millions of acres.

Insect

Ips Bark Beetles

Moderate

A genus of bark beetles that attack stressed and weakened pines throughout North America. While they typically colonize dying trees, drought and overcrowding can trigger outbreaks that kill healthy timber.

Insect

Dutch Elm Disease

Critical

A devastating vascular wilt disease spread by elm bark beetles that has killed millions of American elms since the 1930s. The fungus blocks water-conducting vessels, causing rapid wilting. It fundamentally changed the American urban landscape.

Disease

Powdery Mildew

Low

A widespread group of fungal diseases that produce a distinctive white powdery coating on leaves and shoots. It affects hundreds of tree, shrub, and plant species. Unlike most fungi, it thrives in warm, dry conditions with high humidity.

Fungus

Thousand Cankers Disease

High

A disease complex involving the walnut twig beetle and an associated fungus that has caused significant mortality of black walnut, particularly in western states. Thousands of small cankers coalesce to girdle branches and the trunk.

Disease

Dothistroma Needle Blight

Moderate

A fungal disease of pines that causes premature needle loss and can significantly reduce growth and vigor. It affects many pine species but is especially damaging to Austrian, ponderosa, and Monterey pines. It has increased in severity with climate change.

Fungus

Rhizosphaera Needlecast

High

A common fungal disease of spruce trees, especially Colorado blue spruce, throughout the Midwest and Northeast. The fungus infects current-year needles through stomata, causing them to turn purple-brown and drop prematurely. Inner and lower branches are affected first because humidity is higher there, and the disease progresses upward and outward over successive years. Severely affected trees may retain only the current year's needles at branch tips.

Fungus

View full Colorado tree health guide

Frequently Asked Questions

Should I treat or remove my ash tree in Denver?

If the tree is healthy, well-placed, and worth keeping, trunk-injected insecticide every 2-3 years protects it from emerald ash borer, and ongoing treatment usually beats removal-plus-replacement on cost for a good tree. Thinning canopy, woodpecker flecking, or bark splits mean it's likely infested — remove before it turns brittle and dangerous. An assessment now beats an emergency later.

Do I need to water my trees in winter?

In Denver, yes — winter watering is standard practice. During dry, warm stretches (above 40°F, unfrozen ground), water deeply about once a month, especially young trees and evergreens. Winter desiccation quietly kills more Front Range trees than any insect except EAB.

Who's responsible for the tree between the sidewalk and the street?

You maintain it, but the City Forester regulates it. Planting, pruning, or removing right-of-way trees in Denver requires a permit, and tree companies must be licensed to work in the city. Contact Denver's Office of the City Forester before doing anything to a street tree.

What trees grow best in Denver?

Bur oak, Kentucky coffeetree, hackberry, honeylocust, western catalpa, and crabapples all handle alkaline soil, drought, and Front Range temperature swings. Plant in spring, water the first two summers religiously, and wrap young trunks in winter against sunscald.

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