How to Protect Your Trees from Frost

Mon, December 29, 2014 11:09 AM | Anonymous

Yes, freezing temperatures actually happen in Phoenix. Temperatures below 32 degrees for a prolonged time or over several nights can freeze tree buds/blossoms, fruit, leaves, and twigs. While the trees in our Shade Tree Program are desert-adapted and can, therefore, typically withstand freezing temperatures, young saplings can be vulnerable to the cold weather especially if they haven’t gone into winter dormancy and are, therefore, still actively growing.

The average last frost date in central Phoenix is February 7th (it’s around April 3rd for Mesa) and as we experience freezing temperatures this week, here are some tips for protecting your young as well as frost-sensitive trees from frost:


The best protection is to cover your trees with a sheet, light blanket, or burlap sack.  Hardware stores sell sheets made of light, porous material specifically for frost protection but feel free to use whatever you have on hand except for anything made of plastic. Plastic traps moisture in and can damage the tree (the captured moisture can turn to frost). Also, thick blankets or covers can soak up moisture, become heavy, and press down on the tree. Ideally, you want the cover to touch the ground to retain the warmth under the cloth and around the tree (refer to the left picture and the diagram below). Although it’s recommended to not have the cover touch the leaves or branches, if you’ve ever covered a tree or plant you know that’s quite a task so just do the best you can. 


Remove the cover later in the morning when there is full sunlight and preferably when temperatures are warmer.  Some of the coldest temperature occur at daybreak so if you can, wait a bit. Do not leave trees covered all day as this can damage them. 

  • If your tree gets frost bitten, do NOT trim the damaged parts as they still provide protection for the remaining living parts of the tree. Wait until the spring or when you regularly prune your tree.
  • Make sure to water your trees regularly during winter. Dehydrated trees are more susceptible to frost-- frost damage occurs when ice crystals form on the leaf surface drawing moisture from the leaf tissue so if a tree is already dehydrated, the additional dehydration damages or kills it. Wet soil also absorbs heat during the day so water your plants in the morning and do not overwater. Refer to our blog on How to Properly Water Your Trees.
  • For large trees or frost-sensitive ones such as citrus trees, string 100-watt electric outdoor light bulbs, such as Christmas lights (pictured right). Not only are you decorating for the holidays but you are warming your trees.  Make sure the lights are not too close to the trunk or branch that it could burn it.
  • Place mulch around deciduous trees (like our Shade Trees) to prevent them from breaking winter dormancy by insulating them against fluctuating surface soil temperatures. However, do not place mulch around citrus trees, as it will hinder the capturing of heat that will protect the plant.

Below are some great references for additional information and ideas. As always, if you have additional tips or questions, please post them on our Ask the Arborist forum here and our volunteer Arborist, Erik, will answer them. 


Erik the Arborist, on our forum:                    


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