Proper Frost Protection

Will winter ever arrive? Someone needs to remind Mother Nature that the Desert Southwest wants to experience cooler temperatures at some point. With all our warm fall, plants that normally go dormant have continued to grow, putting some frost-sensitive plants at risk of freezing back when our winter finally does arrive. A plant’s ‘hardiness’ is its cold temperature threshold: the more ‘hardy’ the plant is, the more tolerant it is to cold temperatures. Here are some frost facts to know when preparing your landscape for the (possibly) cold Arizona winters:

  • Frosts occur in Phoenix area anytime from late November until late March
  • Coldest time of day is just after the sun comes up
  • Cloud cover can protect from frost damage by trapping warm air close to earth
  • Calm, clear nights (no wind or clouds) pose the greatest danger of frost
  • Low lying areas get more frost  (hot air rises)  

There are a number of frost protection strategies, including frost blankets, anti-transpirant foliar sprays and even Christmas lights can warm cold-sensitive plants. Frost blankets seem to be the favorite choice in our region, providing up to 8-9 degrees of protection. However, they are often used incorrectly, just covering the top of the plant, which unfortunately does not provide any protection from the cold. Here are a few helpful hints to make sure you are using protective frost blankets correctly:

  • Use cloth or paper, never use plastic!

Sheets or blankets, should be removed daily
Frost cloth can be left on for a few days

  • Drape plant from top all the way to the ground
  • Do not allow any openings (trap heat rising from ground under cloth)- this is the most important part of proper covering
  • Do not gather the drape around trunk
  • Allow drape to cover all the way out to drip line, if possible
  • Wrap trunks of young citrus trees loosely to the ground (can be left all winter)
  • Additional steps to help protect your plants from the cold:

Christmas lights at bottom of plant can radiate heat
Water under canopy adds heat: when water cools, energy is released=heat!
Don’t fertilize- new growth is more sensitive to frost damage
Don’t prune- don’t prune sensitive plants until after threat of frost (late February)
Don’t overprotect- allow plants to harden off, gradually expose to cold weather