Frosts and freezes in the Spring are a hazard to fruit growers because freezing temperatures can kill actively growing shoots and flowers, destroying all or part of the fruit potential for the year. As overwintering buds develop, they become less and less resistant to cold (see the Michigan State University Extension article “Freeze damage depends on tree fruit stage of development”).
At bloom, fruit tree blossoms suffer damage just below freezing at about 28 degrees Fahrenheit. Because it has to get below freezing to cause injury, 28 F is often called a hard frost or a hard freeze to denote that the temperature was below freezing.
In 2012, fruit trees bloomed a month early and the normal freezes of April devastated the Michigan’s tree fruit industries. In 2013, we are one or two weeks behind normal development and tree fruit are only now entering the stage when hard freezes can cause damage. In many parts of southwest Michigan, there is only a 25 percent chance or less of a damaging freeze this Spring. The possibility of a freeze continues to drop into early May. This means there is an excellent chance that there will be no freeze damage to fruit crops because the cool April delayed growth.
The National Weather Service has calculated the probability of a freeze for many of their long-term weather stations using data from 1951 to 1980. The table below is arranged from North to South. Sites located away from Lake Michigan show the approximate distance to the lake. Sites near Lake Michigan show no distance. In the table, 10 percent means there is a 10 percent chance of a freeze occurring on or after that date in the Spring. Many gardeners worry about the last date when a temperature of 32 F will not occur. For more information on frost-free dates, see “Frost free dates: When is the last day my garden will get a frost?”
Source: Michigan State University
