Temperatures have been well above normal so far this spring; however a return to more seasonal temperatures this week will be a concern for area growers. With the growing season 2 to 3 weeks well in advance of what one would consider normal for South Dakota, many trees and shrubs are already in the process of budding, and this sudden dose of reality may have disastrous consequences. So to put in perspective: what have we experienced and what can we expect through the middle of next week…
Using a threshold of 28 degrees (widespread killing freeze) we can quantify the early spring conditions the region has experienced. While sporadic and localized near freezing temperatures have occurred, temperatures have been warm enough to allow plant development through much of March (Figure 1). The latest average time period we can expect this range of temperatures tends to be in mid to late April, and early May (Figure 2), and thus dispite an early start we can still expect cold snaps.
Figure 1. Most recent incident of temperatures falling to 28 degrees or below (widespread killing freeze), for some locations we have to look back 3 weeks ago.
Figure 2. Representation of the average date in which the temperatures has cooled to 28 degrees or below going into the growing season.
With the passage of a cold front early Saturday, a more seasonal Canadian airmass is poised to move into the region. These colder temperatures, while not outside the climatological norm, we lead to a significant change from the mild conditions we have thus far experienced.
Figure 3. 4. & 5. Model representation of temperatures (Celsius) at 1000ft Above Ground Level Monday, Tuesday, and Wednesday Morning.
Young buds are particularly sensitive to cold snaps, especially for fruit trees, as these tend to bloom early and a freeze will kill the majority flower buds. The more open or colorful the bud, the greater the chance of loss.
Covering plants is the simplest, most practical way to protect against frost and freeze. The main source of heat for a plant is the soil, and on a cold night the heat rises up around the plants. Using a blanket or sheet (even garbage cans and cardboard boxes will work) will trap enough heat to keep plant tissue from freezing. During the day, remove the covering to allow the sun to rewarm the soil. Move container plants indoors, they are more susceptible to cold temperatures.