Just like you, it is possible for your plants to get too cold at times. But unlike you, they do not show it by shivering; there are different signs to indicate that a plant is too cold. If hearing that a plant can be "too cold" strikes you as odd, you may prefer the more technically accurate language that the green industry uses to discuss the phenomenon: It is referred to as "cold shock" (or "chilling injury").
What Is Cold Shock vs. Frost or Freeze?
A plant is said to suffer from cold shock when temperatures are too cold for it but do not fall to freezing and no frost occurs. Frost advisories are posted when temperatures are expected to fall to the 32-to-36-degree range (F), whereas a true freeze means the temperature goes to 32 or lower.
Signs that a plant is too cold vary across plant types and regions. Whether you are a Southerner experiencing a sudden cold snap or a Northerner growinga tropical plant in a container outdoors, it's helpful to know the signs of cold shock.
4 Signs That Your Plants Are Too Cold
Even before temperatures drop enough for a plant to be damaged from cold, the plant may stop growing as vigorously as it did in warmer weather. This is normal, but it does serve as a clue for you to be on the lookout for one or more of the four signs that your plant is too cold.
The first three of these signs will be most apparent because they occur on above-ground vegetation; the fourth sign occurs underground and won't be as obvious.
However, be careful not to get your signals crossed. The presence of one of these four signs does not necessarily indicate cold shock. For example, sometimes, when a plant has wilting leaves, it may be due to a disease known as verticillium wilt, too much or too little water or some other underlying cause. It's important to monitor your plant's development throughout the growing season and keep track of the local weather. If a plant has been healthy all along but leaves suddenly droop with the onset of cold weather, the drooping is most likely due to the cold, and not some other cause.
Wilting or Curling Leaves
Healthy leaves have a certain firmness to them. They keep their flattened shape, and stems give the support they need to stick out from their branches. When a plant gets too cold, it may lose this firmness, resulting in curling edges curling edges or wilting.
Not all changes in autumn leaf color mean great fall foliage. Depending on the plant and on the severity of cold shock, leaves in fall (or spring) on affected plants may develop white, yellow, red, or purple spots, brown patches, or (in the worst cases) turn totally black.
Loose Root Ball
The root ball of a healthy plant anchors it to the ground. The root ball of a plant suffering from the cold can be damaged so that, when you tug up even gently on the plant, it is obviously no longer firmly anchored. Root ball damage is the worst sign of cold shock damage: It means you will probably lose the plant.
How Serious Is Cold Shock?
With plants suited for your hardiness zone, you don't have to worry about them dying from getting too cold, Plants hardy in southern zones have less tolerance; some of them start to show signs of cold shock even at 50 degrees (F). It can be a problem even when it damages only part of a plant. The part damaged is often the most anticipated and desired. For example, a cold snap in Florida may ruin an orange crop.
In the North, a cold snap in spring, can kill the buds on shrubs and trees and prevent flowers and fruit from developing. Deciduous trees endure cold temperatures by going dormant during the winter months and evergreens are able to survive due to the small amount of leaf surface subjected to freezing temperatures. These trees can suffer cold damage but rarely suffer signs of shock or succumb to it.
Tropical plants grown in patio containers can be moved indoors when temperatures drop. But vulnerable plants grown in the ground are more difficult to protect. Options include covering the plants with blankets or sheets and heating the area with a patio space heater.