Take a bike ride along any bike trail in Denver, and there is widespread tree damage across the City. Many trees have half-dead crowns, leafless branches, and stunted growth. What happened? The simple answer is Denver’s weather threw some hard pitches and struck out many of the trees growing in our yards, streets, and parks.
Stike One – Polar Plunge
Last October, the temperature dropped from the eighties to the low teens in a day. The 70-degree temperature swing set records in the Denver. The sudden freeze catches trees off guard because the warm weather delays a tree’s hardening process to prepare for winter. Deciduous trees harden by sealing off where leaves attach to the tree. The leaves turn color and eventually drop in the fall. Evergreens hibernate in the winter but keep their needles. Tree hardening or dormancy conserves water and food for the next growing season. Non-hardened trees flash-freeze when the temperature abruptly drops. Some trees show damage immediately, while others wait to show any injury in the spring. Below are examples of freeze damage.
Evergreens – An early freeze kills the new needle growth on Pine trees. The needles turn brown. Most of these trees recover as new needles emerge in the spring.
Deciduous – Frozen deciduous trees keep their foliage over the winter. The brown, dry leaves drop off during the next growing season.
Newly Planted Trees – Newly planted trees are particularly vulnerable to flash freezing. Sometimes it takes an arborist to check if the trees are viable the following spring. If the sapling does not leaf out by June, it is dead and needs removal.
Strike Two – Winter Desiccation Damage
Denver also experienced a mid-winter drought. We got a half-inch of moisture over two months this winter, weakening many trees across the City. Little snow cover increases the chance for winter desiccation damage. Typical winter damage includes leaves turning brown, curling up, and eventually dropping. Drought-induced root injury disrupts the chemical, physical, and biological balance in the soil that is essential for plant and soil health. Trees lose their ability to draw enough moisture and nutrients from the ground, leading to reduced vigor, smaller leaves in spring, and compromised overall health. Trees with winter desiccation damage are less able to withstand late spring freezes.
Since Evergreen trees keep their needles, they need more water to survive because their leaves expire water all winter long. Winter winds compound the problem by pulling more water out of the plant. Evergreens planted on the south or west sides of homes in the Denver area are particularly susceptible to winter desiccation damage because of Colorado’s hot sun and windy days.
Deciduous trees drop their leaves in the fall to conserve moisture but need water since their roots still grow in the winter. During the winter, hardwood tree root systems continue to grow, so they need water to survive. Homeowners with shallow-rooted species such as Maples, Lindens, Birches, and newly planted trees need to take particular care of their trees during winter dry periods.
Below are some winter watering tips:
- Water trees during a warm day before it freezes, so their roots can absorb the water.
- Water your deciduous and evergreen trees up to two times a month between October and March.
- Dig down at least 4-6 inches around the dripline to check soil moisture levels. If dry, the tree needs watering.
- Water deciduous trees within their dripline. For evergreens, water on all sides of the tree several feet beyond their dripline.
Lipstick for Trees
Once your yard evergreens are properly hydrated, coating the nettles and leaves with anti-transpirant products prevents moisture loss. Anti-transpirants are clear wax coatings that prevent trees and shrubs from losing moisture through their foliage. It is like lipstick for trees. Evergreens, like conifers and rhododendrons, are especially susceptible to windburn and sun-scald. Anti-transpirants help them look their best and prevents winter desiccation damage.
Strike Three – Spring Frost Damage
Denver had a very destructive hard freeze in April. Many trees in the Denver area experienced cold-weather-related damage this spring. Late-season snow and frost-damaged young tree branches, leaves, and buds just as the trees were leafing out. Ash trees were hit hard in the City. Actual freeze damage to trees may only range as deep as the outermost leaves and new branches. Given enough time, many frost-damaged trees rebound. But some do not, and it might take a trained arborist to decide the viability of a tree. While on-site, the arborist checks for:
- Frost cracks or radial shakes
- Sunscald canker on trunks
- Winterburn on evergreen trees
- Dieback of twigs, branches, and limbs
- Ice and snow damage to the bark
- Root damage on shallow-rooted trees
- Stunted growth of trees
- Squirrel kill
Sometimes the damage is so bad that the homeowner needs to consider tree removal.
Structural Tree Trimming
Early fall and late spring snowstorms wreck havoc on trees in Denver. Tree pruning to a dominant leader encourages a strong tree structure that resists snow mechanical breakage. Ross Tree embraces ANSI tree trimming standards endorsed by the Tree Care Industry Association. Credentialed ISA Arborists exhibit demonstrable knowledge and skills for the proper care of trees. Ross Tree Company is proud of its three full-time ISA Certified Arborists on staff. Click here to check out our Standards-Based Pruning Handbook.
It is important to remember that the soils and climate around Denver do not naturally support tree growth. Since trees are not native to Denver, it makes sense that they need supplemental fertilizer and water to grow here. Also, most trees in Denver benefit from pruning to promote healthy growth that makes the tree more resistant to storm damage. A well thought out pruning and Plant Health Care regiment keeps tree healthy so that they can withstand Denver’s unpredictable weather and not strikeout.