Even after 50 plus years in the horticulture field, I still have a hard time reigning myself in at the first sign of spring. If the sky is blue and the temperatures are in the 70s for a few days in a row, then I convince myself that spring has fully arrived and my entire garden should be springing into life. Inevitably though, when I make my rounds, several of my prized plants are not yet budding out and I panic, convinced that they are dead and need to be IMMEDIATELY replaced. Before I can do any real harm to the beds, my husband gently removes the shovel from my hands and reassures me that not all plants emerge at the same time – some simply need a warmer soil temperature to wake up from winter’s resting period.
Horticulturists often categorize plants into warm season and cool season plants. Lettuce, spinach, broccoli and cabbage, for example, are commonly referred to as “cool season vegetables, which grow best when air temperatures are in the range of 60 -65 ℉.” What most of us do not realize however, is that in early spring, the soil temperatures can be 10 degrees (or more) cooler than the surrounding air temperatures.
While several factors control impact soil temperatures, two of the most influential are the soil’s type and its moisture content. A dry, sandy soil will warm much more quickly than a heavy, clay soil. Wet soil heats up more slowly than dry soil because a significant portion of the sun’s energy, called latent heat, is used to physically dry out the soil.
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Warm season plants need soil temperatures to reach 60 to 70 ℉ before they will begin to grow. (That’s why tomatoes planted too early will simply stay the same size; they are waiting for the soil to warm up.) Here in the Midwest, some of our favorite flowering shrubs are extremely slow to leaf out. (See below for a partial listing of late season plants.) Although like me you might be tempted to immediately replace them, first check and see if the stems are pliable or if they are showing green under the bark. If the answer is yes to either, then it’s a good bet that the plant is alive and just waiting for its ideal growing conditions. If the answer is no to one or both, then it’s time to be patient and wait a bit longer to see if the plant is viable. As hard as it is to wait, experts suggest waiting until Father’s Day to decide if the plant is alive or dead.
Since I won’t get my shovel back until Father’s Day, I am determined to just relax and let nature take its course. After all, it’s a win-win situation. Either they come back just as beautiful as before, or I get a new plant or two!
SHRUBS
- Crepe Myrtle
- Weigela
- Rose of Sharon
- Azalea
- Rhododendron
- Beauty Berry
- Butterfly Bush
- Hydrangea
