Is it safe to plant our bedding plants, containers, tomato plants, and other transplants yet?
I’m not much of a gambler. My wife Mary is lucky, but in the rare times we’ve visited casinos, her pile of nickels is canceled by my shortfall. Likewise, I’m not a big fan of rolling the dice when it comes to gardening and spring frosts. So when is it safe to plant?
Our parents and grandparents often planted their gardens on Memorial Day (which was May 30, until 1968.) Field crops of wheat, barley, and oats were a first priority. Afterwards there was time to garden. But this also wisely put the task into a fairly frost-free period with warm soil, causing seeds and plants to grow quickly and thrive.
Although our weather fluctuates between early springs and late springs, we can set target dates for planting with a measure of security. We can diminish the gardening gamble with a planting calendar tailored to our region’s growing season and spring frost dates. The old May 30 Memorial Day rule is later than necessary for most of our area.
Let’s examine the calendar’s possibilities. On May 5 there is still a 50-50 chance of a hard freeze. The average date of Fargo’s last spring frost is May 8, according to the National Weather Service. Grand Forks’ is May 12. The region-wide last spring frost occurs between May 11 and May 20. Fargo’s 90 percent frost-free date is May 21 according to the National Weather Service.
These dates are only averages. Frost has occurred in Fargo after all these dates, as late as June 20, 1969.
If you were to choose a 10-day window to do all your gardening, and to minimize risks, the ten days between May 15 and May 25 are the “sweet-spot” of planting for much of our region. Mary and I have always planted the vegetable garden, installed the annual flowers, and potted up the containers during this period with very few brushes with frost. This ten day period in May is the highpoint of yard and garden spring planting. Soil is typically warm, and plants take off and grow rapidly versus early planting in cold soil.
Some vegetables germinate well in cool soil, and can tolerate frost. Peas, radish, lettuce, spinach, kale, onions, carrots, parsnips and potatoes can all be planted in late April and early May. They’re called “cool season crops.” “Warm season” crops suffer if planted in cold soil, and are easily killed near 32 degrees F. Planting Tomatoes, peppers, squash, pumpkin, cucumbers, melons, string beans and sweet corn should all wait until soil and air have warmed, with a preferred planting time around May 20-25.
Happy Gardening! 
