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Gardening in Washington State

2015 Winter Damage to Evergreens: East of the Cascades

Early Fall 2014 proved to be unseasonably warm and dry east of the Cascades. Plant respiration continued at a higher rate than normal for this time of year and, in many cases, irrigation was winterized. This meant that some evergreens were unusually water stressed. The warm and dry fall was followed by unseasonably low temperatures in November. This unusually hard freeze, coupled with the drought stress, meant that many evergreens suffered tissue damage.

Some of the plants seen with winter cold damage are dwarf arborvitae, hinoki cypress, boxwood and ponderosa pine.

Fig 1

Figure 1. Dwarf arborvitae leaf and twig winter cold damage, ranging from leaf necrosis to branch dieback.

Fig 2

Figure 2. Hinoki cypress suffering complete winter kill

 

While leaf necrosis and branch dieback can be unsightly, most of the plants with this winter cold damage will survive. If the leaf buds were not damaged the plant will grow out of the problem. It is important to wait until late spring or early summer to determine the full extent of the damage.

Fig 3

Figure 3. Boxwood showing leaf and twig winter cold damage along specific areas of the plant, such as the top or side.

Fig 4

Figure 4. Ponderosa pine needle winter cold damage ranges from minor needle tip damage to, in severe cases, complete needle necrosis.

 

 

 

Prune out dead branches to clean up plants. Let the new growth expand and grow to fill in void areas. Careful pruning over the next few years will usually bring back the normal healthy appearance of the plant. If branch dieback goes into the dead zone of conifers, the plant many not return to its original appearance and will need to be replaced.

Submitted by: Paula Dinius, August 13, 2015

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