Freeze damage depends on tree fruit stage of development
Damage from freezes depends on the development stage of the fruit crop. These tables allow you to quickly assess the risk for your tree fruit crops.
Temperate fruits can tolerate very cold winter temperatures. As we move into the warmer weather in March, April and May in Michigan, tree and small fruits lose their winter hardiness. As buds swell and development begins, the ability to withstand cold temperature changes with the growth stage. Early swollen buds can often withstand temperatures in the teens (degrees Fahrenheit) without any damage. As buds develop and begin to open, temperatures in the low 20s can cause harm to fruit buds and perhaps developing leaves.
This range of damage coincides with the growth stages and fruit species and even the cultivar. Early in development, there is often a wide range between the temperatures that cause little damage and those that cause severe damage. Early in development, at first green and green tip stages, temperatures need to drop into the teens or lower to cause significant bud damage. As bloom nears, temperatures in the upper 20s can cause considerable harm to an early blooming species or variety and leave other fruit crops unaffected or with only slight damage. Near bloom, the range between slight and severe damage is very small. The stage of bud development determines how susceptible any given fruit crop is when freezes occur.
Michigan State University Extension has two tables for the critical temperatures of tree fruit during development. Tree Fruit Critical Temperatures is a table of common tree fruit with bud stage names and the critical temperature ranges that will cause between 10% and 90% injury to the flower buds, all on one page. Picture Table of Fruit Freeze Damage Thresholds includes the same information and includes pictures. This table is three pages long.
Unfortunately, spring freezes are almost a certainty in any given year. Fruit growers need to constantly assess the stage of development of their crops and the susceptibility to freeze injury.