Why Was Winter 2013-14 So Hard On Our Landscape Plants?

May 16, 2014

I think we’d all agree, the past winter season was a long and difficult one.  Even now, in the third week of May, temperatures are struggling to reach 70°.  And the three overriding questions remain…will summer ever arrive?  How do I explain to my boss, club members, clients, etc. why so many plants look dead after the winter of 2013-14?  And perhaps most importantly, why was this past winter so tough on landscape plants? 

Consider these events important events:

  • As we entered late fall and early winter, soil conditions were very dry.
  • As a result, many landscape plants entered winter under stress or in a weakened condition.
  • Severe low temperatures (before measureable snowfall) caused the soil to freeze to impressive depths.  This could have resulted in root death to sensitive or stressed plants.
  • When snowfall eventually arrived, it blanketed the ground without interruption, persisting until early spring in some locations and ensuring frozen soil until late March/early April.
  • Strong winds seemed to be an everyday occurrence.  When coupled with high light intensity and frozen soil conditions, the damage to evergreens became a foregone conclusion.
  • Finally, low temperatures, the likes we haven’t seen for many years, helped create the perfect storm.

Mitigating Winter Injury

Winter injury may not be immediately apparent when plants resume growth in the spring. Some plants may actually leaf out and appear quite normal for a time, only to decline and die later during stressful summer conditions.  To minimize unsightliness and promote plant health, dead wood should be pruned out as it becomes apparent. 

Providing appropriate amounts of water to compromised plants may be the most important task for landscape managers.  Plants already suffering from winter injury may die quickly if forced to cope with drought stress.  Mulching the area around trees and shrubs with organic materials like wood chips or shredded bark will help conserve soil moisture and keep lawn maintenance equipment away from sensitive bark and stem tissue. 

Finally, it is important to remember that fertilizer is not a cure-all for winter-injured plants.  If a soil test determines that mineral elements are deficient, then applying an appropriate fertilizer makes perfect sense.  But high rates of fertilizer will not miraculously close sunscald wounds, restore life to killed roots or buds, or reverse any of the other negative effects resulting from the memorable winter of 2013-14.

Jeff Iles

Department of Horticulture

Iowa State University

Below you will fine a few pictures taken by Dr. Iles around Ames.