Every spring, I wait in suppressed panic to see whether my plants made it through the winter, and to see whether I’ll need to do just some judicious pruning or whether I need to replace the plant. Especially this year, with constant deep snows in the Northeast and deep, blizzard snow in the Midwest—followed by a long, cool, spring—the wait has been nerve-wracking. So after weeks of daily observation, when I’m afraid the plant might be dead, that first smattering of tiny green leaves causes me to break out in a small fist-pump and say to myself, “Yes! It’s baaack!”
You’d think that someone of my experience would pay attention to degree days, rather than launching into panic mode; but I can be just as irrational as the next gardener when spring approaches. Growing Degree Days, to those unfamiliar with the term, are units of temperature used to measure either likely insect emergence or anticipated plant development. To determine Growing Degree Days, you use a special thermometer which will record the high and low temperature of the day. You then add those two numbers together, divide by 2 to obtain the average temperature, and subtract 50° F. (10° C.), which is the typical temperature for active growth to begin. Then you add those numbers to determine how many GDD units have occurred so far during the calendar year. An easier way is to subscribe to your local cooperative extension’s newsletter. The newsletter usually contains an update on growing degree days by area of the state.
So here are some of my observations on rate of emergence, and I hope they’ll either keep you from hyperventilating or help you to realize that you need to replace the plant. Please offer any of your own observations in the comments, especially if you’ve noticed any plants that seem particularly slow to emerge in the spring.
Anemones Japanese Anemone
Gleditsia triacanthos Honey Locust
Hibiscus syriacus Rose of Sharon
Hypericum St. Johnswort
Fraxinus Ash Tree
Acer Maple Tree
Perovskia Russian Sage
Euonymus alatus Burning Bush
Ligularia Leopard Plant