To Plant or Not to Plant
Pat Guinan
State Climatologist
Commercial Agriculture/University of Missouri Extension
The unusually mild March weather this year has been tempting for farmers to get an early start on planting, but they may want to think twice before revving up their tractors. Every spring there's the possibility of Canadian air masses diving southward and bringing freezing temperatures to Missouri as late as the middle of May. However, if we have an understanding of climatological probabilities and pay close attention to weather forecasts, which predict one to two weeks in advance, we generally can make some good decisions on when to plant and avoid the icy fingers of Jack Frost.
One of my favorite resources for outlooks beyond 5 days out to two weeks is the Climate Prediction Center web site. Everyday, in the mid-afternoon, 6-10 day and 8-14 day outlooks for the United States are issued by experts from the Climate Prediction Center in Camp Springs, MD. These experts use the latest in weather technology to assimilate and issue outlooks for temperature and precipitation trends. Fortunately, improvements in computer technology and better forecasting techniques and methods have translated to more accurate extended outlooks. The 6-10 day and 8-14 day outlook can be accessed at
Climatology can also be a tool to use when determining the probability for freezing temperatures in Missouri. When it comes to springtime planting in the garden and field, we must be careful not to start too early. A warm spell in March or early April does not guarantee the end of freezing temperatures for the rest of the season. If you know when the average date of the last spring frost is for your area, and you have a good idea of how topography can affect temperature, you can use that knowledge in deciding when may be a safe time to plant and avoid freeze injury. The following web link displays a map of Missouri and the average date of the last spring frost (≤ 32°F):
http://agebb.missouri.edu/weather/frost.htm
Using historical temperature records, the average last spring frost date is defined as the day after which there is a 50 percent chance of a light killing frost. The average date for the last moderate freeze (24-28°F) ranges from the last 10 days of March in the Bootheel to the first week of April across most of southern and central sections, to early into the second week of April over northern Missouri.