Freeze, Drought and Damage to Trees by Heather Duncan

A frost-damaged tree. (Courtesy of Colorado State Forest Service)

In early October 2019, we experienced an extreme weather event when from October 9-11 our front range temperatures dropped from highs in the upper 70’s to lows in the 10’s or even single digits before rising again to the mid 60’s.  Most of our trees had not yet hardened off for winter causing a range of damage. While weaker trees may have suffered more severe damage, healthy trees likely weathered this event with minimal damage such as blackening or browning of leaves on deciduous trees or “grizzled” foliage on evergreens. 

Many of our healthy trees hold enough reserves to handle a single event like this so any longer-term damage would necessitate additional stressors and Mother Nature never disappoints!

Over this past winter, we experienced a short period of drought during December and January.  The front range received only three weather events that brought any measurable precipitation during those months.  The dry winter conditions likely added additional pressure to our trees, especially to those that did not receive any supplemental water during this period.  Signs of winter injury might include browning or rust colored needles on evergreens and sun-scald or leaf scorch on deciduous trees.

Photo: Mary Beth Mainero

Photo: Heather Duncan

Normal Needle Drop
Photo: Heather Duncan

And to add this…in April 2020 temperatures plunged again!  While many spring plants can tolerate light freezes or temperatures of 29º Fahrenheit, we experienced another deep freeze just as many trees were budding and beginning to flower.  From April 10-13 our temperatures dropped from highs in the upper 60’s to lows well below freezing and into the teens.  Not only did this freeze result in a Disaster Declaration for our Western Slope from the USDA, many of our other trees around the state, already stressed by the previous drought and early fall freeze, suffered additional damage such as leaf or flower buds being killed or leaf distortion.

Photo: Heather Duncan

But don’t dismay!  While flower buds are gone for this season and you’ll likely have to wait for next year to see those again, most healthy trees and shrubs have enough reserved energy to form a second flush of leaves.  Many of our trees on the front range have already leafed out again.  Here are some tips and resources linked below on how to manage your trees going forward:

·      Water appropriately:  if there isn’t rain or snow in the forecast, water the root zone to a depth of around 12 inches once or twice per month (even over the next winter) however be careful to not overwater

·      Mulch: applying mulch under a tree may help reduce moisture loss and competition from turf and improve moisture penetration into the soil

·      Hold off on the fertilizer: wait until the tree has fully re-leafed

·      Watch and wait for continued leaf and needle emergence:

o   check for soft/pliable limbs and buds (alive) or dry/brittle limbs and buds (dead)

o   healthy trees will likely form new buds this summer and over the coming seasons will fill in the gaps

o   only prune out dead branches after new growth has emerged and do not prune any living tissue

And for additional information, as always, the Jefferson County Colorado Master Gardeners are here to support you.  Please visit our website at https://cmg.extension.colostate.edu/.

Additional information is available:  Western Slope, Woody Plants, CSU-Woody Plants, 
ColoStateForestService