Q. I have two blue atlas cedars (Cedrus atlantica 'Glauca') that are completely brown after this winter. Are they dead or is the foliage just burned?
A. Blue atlas cedar is rated as hardy to USDA Zone 6. Much of Allegheny County is listed as Zone 6a, with low winter temperatures ranging from minus-5 to minus-10 degrees, but the City of Pittsburgh is rated as Zone 6b, with winter lows from 0 to minus-5 degrees.
Whether they live or not depends in part on where you live. If you are in an urban area, where buildings and pavement hold more heat than suburban and rural areas, the foliage may just be burned and they will survive. If you live in the suburbs, especially the northern suburbs, they may not.
It also depends on how long they have been growing -- established plants have a better chance of surviving extremes than those that are newly planted. Likewise, plants that go into winter well hydrated and healthy will fare better than those that are stressed by drought or insect and disease problems.
In addition to brutally cold temperatures, strong winds play a role. While needled evergreens usually have a waxy coating on their needles that helps minimize moisture loss, blue atlas cedar needles are not as heavily waxed as many spruce and pines. Strong winds pull moisture through the stomata (pores) in the needles, but plants cannot take up additional moisture from frozen ground to make up for the loss. The result is the browning you see on the foliage of your blue atlas cedars. This type of damage is very evident on broadleaved evergreens such as English ivy, euonymus, pachysandra and rhododendron.
The bottom-line with your blue atlas cedars: Wait until they should start showing new growth as temperatures warm in spring. The brown needles will drop and new growth will start covering those bare branches if the foliage was just burned. If that does not happen, then they did not survive the polar vortex.
The revised USDA Hardiness Zone map and climate change have many gardeners pushing hardiness zones with plants that are marginally hardy for us, including crapemyrtle, camellia and photinia. That is fine, as long as losing these tender gems to a harsh winter doesn't break the bank. Again, some of these plants might die to the ground and come back from the roots, so do not be in hurry to dig them up. Give spring a chance to finally arrive and see if they show any signs of life, especially crapemyrtle -- it is very slow to come to life in spring.
Even plants that are generally hardy to Zone 5 may show dieback or other signs of damage when spring arrives. Spring-bloomers such as forsythia, big-leaf hydrangea and evergreen azaleas may only bloom close to the ground, where flower buds were protected by snow cover. Be patient and see what spring brings.
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