April 7, 2016

Critical Temperatures For Frost Damage on Fruit Trees

This spring has marked another unprecedented weather pattern that raised our temperatures in late March and lowered early April temperatures to below normal.  It seems that each spring since 2012, we have been on the verge of critical temperatures for frost damage with our fruit trees.  

As the trees develop in the spring and buds start to swell, they lose the ability to withstand the cold winter temperatures that they could withstand in dormancy during the cold winter months. The young, actively growing tissue can then be damaged or even killed. Swollen fruit buds can better withstand temperatures in the teens without any damage. As the buds open, temperatures in the low 20s can cause harm, but sometimes leave other buds undamaged.  As growth moves from green tip to 1/4” green to 1/2” green to tight cluster to pink in apple trees, temperatures in the upper 20s can cause considerable harm to an early blooming tree. Near bloom, the range between slight and severe damage can be very small. So the stage of bud development determines how susceptible any given fruit crop is when freezes occur.  For more information on what those critical temperatures are that can cause freeze damage to trees during development, I have added two charts on the Critical Temperatures For Frost Damage on Fruit Trees from Utah State University below that you can download by clicking on either chart below. 

http://royaloakfarmorchard.com/pdf/Critical_Temperatures_Frost_Damage_Fruit_Trees_Utah.pdf 

http://royaloakfarmorchard.com/pdf/Critical_Temperatures_Frost_Damage_Fruit_Trees_Utah.pdf
 
Given the weather patterns we have experienced so far this spring, and the fact that we have gotten snow as late as mid April, a spring frost could be possible within the next few weeks.  We will need to constantly assess the stage of development our trees are at and their susceptibility to freeze injury. If we continue in this spell of colder weather, apple trees will continue to develop more slowly, but once they begin showing tight cluster and pink, the critical temperature rises from the low 20’s to the high 20s, to levels just below freezing at bloom time.  

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