When Mother Nature decides to turn the thermostat down below freezing, it affects more than just water lines and power bills. Many plants develop wilted leaves, blackened stems, and may look as if they’ve been scorched. Others will not show signs of damage until spring, when they come out of dormancy. The following is a brief explanation of what is actually happening when plants freeze and how to properly deal with the results of freeze damage.
When temperatures drop below freezing, it isn’t just the cold air that affects plants — it’s the physical and chemical effects of ice forming in and around plant tissues. In most freezing events, water freezes outside the cell walls, in spaces between individual cells called the apoplast. Once ice crystals form in the apoplast, water inside the cells is pulled out through osmosis (the movement of water across a membrane to balance solute concentrations). This process effectively dehydrates plant cells, making them more vulnerable to injury. Dehydration alone can damage cell membranes and disrupt normal metabolism, even if the water inside the cells has not frozen.
If freezing continues and temperatures keep falling, ice may eventually form inside the cells themselves. Water increases in volume by about 9 percent when it freezes, and this expansion can physically rupture cell membranes and cell walls. Once a membrane is punctured or torn, the cell can no longer maintain its internal balance and will quickly die. Dead plant tissue often appears brown, blackened, or water-soaked once the plant thaws. Leaves and stems may wilt because dead cells can no longer maintain turgor, or internal pressure.
In woody species, repeated freezing and thawing can introduce air bubbles into water-transport tissues (xylem), blocking water movement when temperatures warm. This condition, known as embolism, can deprive plants of water even after temperatures rise, compounding stress. In some cases, freeze damage is not immediately visible and may take days or even weeks to appear, especially in older tissues or damaged buds.
Why do some plants survive freezing temperatures while others do not? Plants differ greatly in their cold tolerance. Cold-hardy plants are able to increase protective solutes, such as sugars and proteins, which help lower freezing points and stabilize cell membranes. This natural process allows these plants to survive winter conditions with little or no injury. The best thing to do with freeze-damaged plants right now is often nothing at all. Winter is not over, and additional freezing temperatures are likely. Extension experts recommend leaving damaged leaves and stems in place until the danger of further freezes has passed and new growth begins in spring. Even unsightly dead material can help insulate living tissue from cold temperatures. To check whether branches are alive, gently scrape the bark with a fingernail. Green cambium tissue beneath the bark indicates living wood, while brown or black tissue suggests freeze injury. Prune back to firm, healthy tissue only after consistent new growth is observed.
