When to Plant?

​Usually the question is plaintively asked:  “I can’t wait to plant, is it time yet?”  The answer is a bit more complicated for northern gardeners than you might expect.  When I lived in southern Wisconsin I planted my garden and containers successfully all at the same time near Memorial Day.  When I moved almost 300 miles to northern Wisconsin using the calendar method no longer worked.  It took a while to figure out why my seeds failed to germinate and the nursery plants grew ever so slow.

​There is a lot of folk wisdom regarding planting.  Pick up any farmer’s almanac and there is plenty of advice.  Some folks go by the calendar like I did in southern Wisconsin.  My Dad swears that potatoes should be planted on St. Patrick’s Day.  Other methods include moon phases, phenology, weather, and soil temperatures.  I now rely on my soil thermometer that was purchased for less than $10 at the local hardware store.  But what method should you use?   You decide.
 
​Calendar   As I have learned the calendar method is only as reliable as a gardener’s experience.  This method led to my failure because I was naïve and inexperienced about northern Wisconsin gardening.  But I had been successful with this method for over 4 decades.  Bottom line:  it is simple and effective when used correctly.
 
Weather   Last frost dates in the spring and first frost in the fall are determined by the National Weather Service averaging 30 years of data.  The forecast predicts the last frost date and first fall frost using a probability of 50% chance that the prediction will prove true in any year.  When I look at the handy chart the Weather Service provides  it tells me that Winter Wisconsin has a 50/50 probability of the last frost being May 30.  The chart also tells me dates for probabilities of 10% and 90% if I want to take more or less risk of frost or freeze.   Chart: https://www.ncdc.noaa.gov/climatenormals/clim20supp1/states/WI.pdf 
 
Moon Phases   Most almanacs will provide a chart of moon phases along with optimum planting dates.  The basic premise is that as the new moon rises the lunar gravity pulls water up and causes seeds to swell and burst.  As the moon moves into the second quarter it allows for strong leaf growth and generally a good time to plant warm weather plants such as tomatoes, beans, and peppers.  In the third quarter the gravitational pull is high creating more moisture in the soil and a good time to plant root crops.  Finally the fourth quarter, as the moon is waning, is a resting period and good for cultivation and harvest.  This offers a rhythm to various gardening tasks. 


Phenology   My Grandpa Walter said “plant the garden when oak leaves are as big as a squirrel’s ear.”   He didn’t know it but he was practicing phenology, the study of the relations between animal and plant life.   Nature knows the best time to begin its growing season.  I can watch certain plants for clues on timing my gardening activities.  I keep this list in my journal to watch every year:

• Plant peas when forsythia blooms
• Plant potatoes when the first dandelion blooms
• Plant beets, cole crops, lettuce, and spinach when lilac is in first leaf
• Plant bean, cucumber, squash when lilac is in full bloom
• Plant tomatoes when lily-of-the –valley blooms

 
Soil Temperature   I’ve discovered that soil temperature is my best predictor of proper planting time.  I keep a chart I found on the web that provides the minimum and maximum range for vegetable seed germination.  It tells me that spinach and lettuce will germinate as low as 35° but the optimum is 70°.  I pay more attention to the best temperature to plant green beans since I want those as early as possible.  The minimum is 60°; optimum is 80°.
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 This year I planted my green beans on May 14 because the soil temperature was 60°, lilacs were just starting to bloom, and there was a 10% chance we were past our last frost.  It has rained almost every day in the past week with temperatures only barely getting above 50.  I took another soil reading and the temperature has dropped to 50° and we had a frost warning from the National Weather Service this week.  It doesn’t bode well for those bean seeds.