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Wednesday, November 21, 2012

Lets Hope for a Gradual Drop in Temperatures This Fall

            Normally we enjoy very nice fall weather in Las Vegas until about the first week of December and oftentimes without frost. This would be pretty normal. To have freezing weather before this, or unusually cold weather, would be a bit odd. As long as the temperatures continue to drop slowly to our winter minimum lows our perennial plants that can withstand some light freezing weather will survive the winter.

Cold temperature damage to cycad. Notice there is more damage closer
to the ground where cold temperatures lay.
            If November temperatures drop suddenly, or we have snow before trees drop their leaves, then we can have problems. If we are enjoying, for instance, night time temperatures just falling below 50F and then it suddenly drops to 30F the next night, then we might see major freezing damage in plants that normally might tolerate temperatures to 20F. To survive the winter minimums, winter-tender plants need time to acclimate to these low temperatures so that they can create their “antifreeze” if they are to survive.

            Decreasing fall and winter temperatures also helps leaves to drop. One good cold snap in the fall can cause tree leaves to drop prematurely. One day the leaves are there and in just three or four days after the freeze, they are on the ground. Trees like ash and Chinese pistache don’t please us with their winter colors when this happens.

Reader's African Sumac with snow damage during the snow of December
2008. You will need to get out and hit the limbs with a broom during
heavy snow falls.
            There is a good side to this early leaf drop. If we have one of our “every five year” snow events, and it comes after early leaf drop, we miss all the damage snow can cause that time of year. If snow comes early and these trees have not dropped their leaves, then we can have massive limb breakage due to the snow load on limbs.

            How we manage winter-tender plants going into the fall months can make the difference between their survival and death from winter freezes. It is important to withhold fertilizers, particularly nitrogen, during and after the month of August. It is also important to change the irrigation clock so that water is delivered less frequently that time of year.

            If winter-tender plants are still pushing new growth or they are still succulent at this time of year, there may not be enough time for them to begin their adjustment for winter cold. This adjustment takes them a couple of months of decreasing temperatures and longer nights to accomplish this.

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