When to plant in Harvard, IL

Planting dates worked out from Harvard's own frost records, not a generic zone chart.

Safe to plant out

May 15

1 year in 10 has a later frost

Average last frost

May 5

about a 50% chance of a later one

Average first fall frost

Oct 7

1 year in 10 by Sep 24

Frost-free days

151

median, 1991–2020

Station used: Marengo · 17.6 km away · station 248 m, town 292 m. How we match towns to stations

This season

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Planting dates for common crops

Crop	Start indoors	Plant out or sow	Harvest from
Tomato	Mar 20 – Apr 3	May 15 – May 29	Jul 9
Sweet pepper	Mar 6 – Mar 20	May 15 – May 29	Jul 14
Lettuce (leaf)	Mar 3 – Mar 10	Apr 7 – Apr 21	May 17
Peas	—	Apr 3 – May 1	May 28
Bush beans	—	May 8 – May 29	Jun 27
Carrot	—	Apr 14 – May 26	Jun 13
Beet	—	Apr 14 – May 26	Jun 3
Potato	—	Apr 14 – May 5	Jun 23
Kale	Feb 27 – Mar 13	Apr 10 – Apr 24	May 23
Broccoli	Feb 24 – Mar 10	Apr 7 – Apr 28	Jun 6
Cucumber	Apr 17 – Apr 24	May 15 – May 29	Jul 4
Summer squash and zucchini	Apr 17 – Apr 24	May 15 – May 29	Jun 29
Winter squash	Apr 17 – Apr 24	May 15 – May 29	Aug 3
Sweet corn	—	May 8 – May 29	Jul 7
Onion (from sets)	—	Apr 7 – Apr 28	Jul 6
Garlic	—	Sep 23 – Oct 21 (fall)	following summer
Spinach	—	Apr 3 – May 1	May 11
Basil	Apr 3 – Apr 17	May 15 – May 29	Jul 11

Plan all 65 crops for Harvard

Harvard's weather over time

How the growing season has shifted here, year by year, from the station's own records.

Each year's last spring frostLong-term trend

See the data as a table

Year	Last spring frost
1893	Apr 24
1894	Apr 12
1895	May 21
1896	Apr 10
1897	May 1
1898	Apr 20
1899	Apr 19
1900	May 4
1901	Apr 21
1902	Apr 20
1903	May 1
1904	Apr 22
1905	Apr 22
1906	May 9
1907	May 20
1908	May 3
1909	May 4
1910	May 14
1911	May 3
1912	Apr 23
1913	May 10
1914	Apr 21
1915	Apr 13
1916	May 18
1917	May 23
1919	Apr 26
1920	May 14
1921	Apr 18
1922	Apr 29
1923	May 13
1924	May 1
1925	May 25
1926	May 4
1927	Apr 30
1928	May 12
1929	May 19
1930	Apr 27
1931	May 4
1932	May 2
1933	Apr 27
1934	Apr 28
1935	May 4
1936	Apr 23
1937	Apr 16
1938	May 13
1939	May 12
1940	May 11
1941	May 10
1942	Apr 21
1943	May 1
1944	May 5
1945	Jun 5
1946	Apr 27
1947	May 10
1948	May 8
1949	May 28
1950	May 2
1951	Apr 27
1952	Apr 16
1953	May 13
1954	May 7
1955	May 18
1958	May 9
1959	Apr 22
1960	May 12
1961	May 26
1962	Apr 21
1963	May 23
1964	Apr 25
1965	May 29
1966	May 11
1967	May 12
1968	May 6
1969	Apr 30
1970	May 7
1971	May 12
1972	Jun 11
1973	May 17
1974	May 7
1975	Apr 26
1976	May 8
1978	May 6
1979	May 1
1980	May 9
1981	May 12
1982	Apr 28
1983	May 10
1985	Apr 10
1986	May 4
1987	May 5
1988	Apr 30
1989	May 7
1990	May 11
1991	Apr 23
1992	May 27
1993	Apr 27
1995	Apr 25
1996	May 13
1997	May 16
2003	Apr 23
2004	May 3
2005	May 4
2006	Apr 26
2010	May 10
2011	May 4
2012	Apr 27
2013	May 13
2015	May 1
2016	May 15
2017	May 8
2018	May 1

Each year's frost-free daysLong-term trend

See the data as a table

Year	Frost-free days
1893	173
1894	179
1895	131
1896	179
1897	180
1898	177
1899	163
1900	165
1901	164
1902	176
1903	169
1904	183
1905	172
1906	153
1907	127
1908	148
1909	160
1910	161
1911	173
1912	182
1913	134
1914	186
1915	177
1916	120
1919	167
1920	139
1921	168
1922	170
1923	159
1924	151
1925	136
1926	144
1927	171
1928	134
1929	121
1930	157
1931	180
1932	156
1933	168
1934	182
1935	152
1936	182
1937	163
1938	163
1939	140
1940	137
1941	170
1942	156
1943	147
1944	158
1945	116
1946	156
1947	138
1948	157
1949	118
1950	144
1951	153
1952	169
1953	146
1954	152
1958	144
1959	148
1960	159
1961	124
1962	152
1963	143
1964	155
1965	127
1966	142
1967	152
1968	150
1969	166
1970	149
1971	134
1973	151
1974	137
1975	153
1976	136
1978	154
1979	158
1980	147
1981	142
1982	170
1983	156
1985	178
1986	154
1987	150
1988	157
1989	139
1990	152
1991	150
1992	124
1993	155
1995	150
1996	142
1997	151
2003	160
2004	152
2005	171
2010	146
2011	150
2012	149
2013	159
2015	168
2016	151

Each year's average temperature, April to SeptemberLong-term trend

See the data as a table

Year	Growing-season temperature
1893	16.6 °C
1894	18.1 °C
1895	18.3 °C
1896	18.1 °C
1897	17.3 °C
1898	17.8 °C
1899	18.4 °C
1900	18.4 °C
1901	18.4 °C
1902	16.4 °C
1903	16.8 °C
1904	16.3 °C
1905	17.1 °C
1906	18.2 °C
1907	15.4 °C
1908	17.7 °C
1909	16.6 °C
1910	17.6 °C
1911	18.3 °C
1912	17.1 °C
1913	17.6 °C
1914	17.9 °C
1915	16.3 °C
1916	17.4 °C
1917	15.6 °C
1919	17.8 °C
1921	19.8 °C
1922	18.7 °C
1923	17.5 °C
1924	15.7 °C
1925	18.2 °C
1926	16.4 °C
1927	16.7 °C
1928	16.4 °C
1929	16.7 °C
1930	18.2 °C
1931	18.4 °C
1932	17.9 °C
1933	18.6 °C
1934	19.4 °C
1935	16.8 °C
1936	18.6 °C
1937	17.9 °C
1938	17.9 °C
1939	18.3 °C
1940	17.0 °C
1941	18.9 °C
1942	17.8 °C
1943	17.4 °C
1944	18.5 °C
1945	16.5 °C
1946	17.9 °C
1947	17.8 °C
1948	18.4 °C
1949	18.2 °C
1950	16.3 °C
1951	16.0 °C
1952	18.1 °C
1953	17.7 °C
1954	17.9 °C
1955	19.3 °C
1957	17.7 °C
1958	17.0 °C
1959	18.6 °C
1960	17.5 °C
1961	16.7 °C
1962	17.4 °C
1963	17.6 °C
1964	18.6 °C
1965	17.7 °C
1966	16.9 °C
1967	16.5 °C
1968	17.8 °C
1969	17.8 °C
1970	18.6 °C
1971	18.0 °C
1972	17.1 °C
1973	17.9 °C
1974	17.2 °C
1975	17.5 °C
1976	17.4 °C
1978	18.3 °C
1979	17.5 °C
1980	17.2 °C
1981	16.9 °C
1982	16.8 °C
1983	17.5 °C
1985	17.6 °C
1986	17.7 °C
1987	18.4 °C
1988	18.9 °C
1989	16.7 °C
1990	17.0 °C
1991	18.5 °C
1992	15.6 °C
1993	16.8 °C
1995	18.0 °C
1996	16.5 °C
1997	16.6 °C
2003	17.2 °C
2004	16.9 °C
2005	18.9 °C
2006	18.1 °C
2009	16.4 °C
2010	19.0 °C
2011	17.2 °C
2012	18.5 °C
2013	17.1 °C
2014	16.4 °C
2015	17.8 °C
2016	18.1 °C
2018	17.8 °C

What this means for you: Since 1893, Harvard's last spring frost has stayed at about the same time of year. The frost-free season has shrunk by about 1 days per decade. Year-to-year swings are large, so keep using the safe date rather than the trend.

Source: daily records from Marengo (NOAA GHCN-Daily). Years with too many missing days are left out.

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