Help for Freeze-Damaged Landscapes

This entry was posted Friday, 7 January, 2011 at 10:46 am

By Cathy Rymer, City of Chandler

Even in the desert freezing temperatures can occur causing damage to many landscape plants and making them look a bit ‘toasted’.  While many frost-sensitive plants can tolerate freezing temperatures for brief periods, nights that dip into the low 30’s or below for several hours can be deadly for even the hardiest of plants.

Trees that are the most vulnerable to freezing temperatures include Ficus nitida, Jacaranda, citrus, young Sissoo, Royal Poinciana, citrus and tropical fruits.

What can you do now?  First, resist the urge to prune off any dead or damaged foliage for a few more weeks.  Even the crispy leaves and stems will act as an insulator and protect the interior of the plant against any future frosts.  You may not be able to protect a large tree completely so focus on protecting the trunk from the soil line up. If the temperature dips below 20 to 22 degrees, a heat source may be necessary. Christmas tree lights or a mechanic’s light will work.  If the tree is small, fashion a tent around the whole tree or base and heat it with. Turn the light on in the afternoon and leave it on until mid-morning the next day.

You don’t need to be overly fussy about the covering. Agricultural fabric, sheets and blankets work well and the seal does not have to be tight. This may be the one time to use plastic to make a tent, as it retains heat well. Just be aware any leaves that touch the plastic will likely burn. Of course, the survival of the plant or tree is most important. Also, use caution when using a heat source with plastic covering. A hot bulb will melt plastic.

Typically our last frost date occurs in late February, although there have been rare occasions where frosts have been recorded in March.  Waiting until then will actually make it easier to tell where tissue damaged by the freezes ends and live tissue begins.  As new leaf buds emerge the green color will indicate where it is safe to prune away the dead foliage or stems.

If you’re in doubt about pruning you may want to consult a professional.  The Arizona Community Tree Council web site has a listing of certified arborists and tree care specialists at  www.aztrees.org.

Best Time to Prune (Phoenix & Tucson metro areas)

Desert Adapted Trees Early summer (May – early June)
Desert Adapted deciduous trees During winter dormancy (January)
Conifers (pines, junipers, cypress) During winter dormancy (January)
Citrus Don’t prune except for hazards or health
Frost-sensitive trees and shrubs Remove damaged foliage after danger of frost has passed (late February into March)

To learn more about the correct pruning of desert plants try “Pruning, Planting & Care”, by Eric A. Johnson. It is filled with great information and step-by-step instructions. ISBN 0‑9638236‑5‑1.

The University of Arizona has a wealth of information on-line.  Try AZ1002 Frost Protection http://cals.arizona.edu/pubs/garden/az1002.pdf

Better yet, make plans to attend one of the free Homeowner Tree Care workshops offered by ACTC.  Check the on line calendar for a dates and locations near you. www.aztrees.org