CHARLOTTE, N.C. — The growing season has started and now we are set to see a pretty decent freeze Thursday night and again Friday night. These won't just be light freezes or frosts either and many area gardens, plants, and crops could be damaged.
Frost vs Freeze:
Frost can occur when the temperature is still above freezing. Since the air temperatures it measured about 5-7' above the ground it can sometimes be even colder at ground level or on surfaces that cool faster than the air. For this reason, you can see a frost even at 34-38°. A freeze is pretty straight forwards being 32.0° or lower. In the case of this week, we will be well below that in the upper 20s to around 30°.
What can you do?:
- The first thing you can do is bring the plants inside or bring them closer to the house if possible. Inside is warmer of course but being close to the house to other objects allows their radiant heat to help keep the plant slightly warmer than the surrounding area. Like shade during the day which blocks the sun and keeps you cooler. The opposite happens at night, the more of the sky that the plants see the colder it is. That's why open areas like your rook or grass will have frost and not under your trees.
- Next cover them if you can with sheets or cloth. Plastic is a last resort because if you leave it on too long the next morning you can damage the plants. If you use plastic keep above the plant and don't let it touch the leaves. With any covering make sure you remove them promptly in the morning after to make sure the sun does not damage your plants.
- Water, water, water. Heavy watering by day can help the soil and plant retain more heat. Water has a high specific heat so it takes a lot of energy to warm it up but also to cool it. Even as a last-ditch effort watering the plants and crops at night will work. Even if ice forms this helps keep the plant warmer. When water freezes heat is removed from the water to cool it, that heat has to go somewhere and it goes into the plant and surrounding air. So the process of ice formation actually creates some heat.
We also worry about all our amazing fruit trees in the Carolinas including the Peach crop. Luckily we can stay clear of damage depending on the phase of the blossoms. When the fruit trees have full blossoms they are the most vulnerable. This is when you can lose 90% of the crop if the temperature is cold enough. We saw killing freezes like this in 2007 when over 90% of the crop was lost of a very late season freeze in the low 20s Easter weekend that year. We then saw a very similar freeze in late March 2017 when we lost 90% of the crop. This was not a very late freeze but we had such a warm February and early March the whole peach tree crop was ahead by almost a month when the freeze happened.