Growing season is defined as continuous temperatures > 32F,
following the last freeze in Spring and prior to the first freeze in the Autumn.

Year 2009:  Last spring temperature < 32 F was April 28 and
Year 2009:  First Autumn temperature <32 F was October 4,
for a growing season of 158 days.

LINK:  Lincoln's First Freeze Climatology, 1887-2009

123-year, 1887-2008 average growing season length: 172 days.
Standard 30-years, 1971-2000, average growing season length: 162 days.
The last 30 years, 1980-2009, average growing season length: 161 days.
Year 2009 Growing Season Length = 158 days.