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.