Fruit trees begin to experience damage when the temperature drops below 32°F, but the actual temperature that causes harm depends entirely on the tree’s stage of development. A fully dormant tree in winter can often tolerate temperatures well into the single digits or below zero without injury. However, once the tree breaks dormancy and the flower buds begin to swell, their tolerance to cold rapidly decreases, with temperatures in the mid-to-high twenties causing significant flower bud loss when the tree is in bloom. Protecting the potential fruit crop requires a multi-layered approach that includes long-term preparation and immediate, active defense when cold air threatens.
Preparing Trees for Expected Freezes
One of the most effective preparatory measures is providing a deep watering 12 to 24 hours before a freeze event. Moist soil holds considerably more heat than dry soil because water has a higher heat capacity and is a better thermal conductor. During the day, wet soil absorbs solar energy, and at night, this stored warmth is radiated upward toward the tree canopy, providing a small but often sufficient buffer against a radiation frost.
The application of a thick layer of organic mulch around the tree base helps insulate the root zone, which is especially vulnerable in younger trees. This mulch should be spread several inches deep but must be kept from directly touching the trunk to prevent moisture buildup and potential pest or disease issues. For young or thin-barked trees, protecting the trunk itself is also a useful measure.
Painting the trunk with a diluted white latex paint helps prevent sun scald, which occurs when the sun warms the dark bark during the day, followed by rapid cooling at night, leading to cracking. Alternatively, wrapping the trunk of a young tree with commercial tree wrap or burlap offers a physical layer of insulation against extreme temperature fluctuations. These foundational steps enhance the tree’s natural resilience before active freeze protection becomes necessary.
Immediate Protection Strategies During Cold Snaps
Active protection involves covering the tree, which traps ground heat and blocks the radiative heat loss that occurs on clear nights. Use materials like old blankets, burlap, or dedicated frost cloth, ensuring the cover extends all the way to the ground to completely enclose the space beneath the canopy. This creates a small, warmer microclimate by capturing the heat radiating from the soil.
It is important to avoid draping plastic sheeting directly onto the foliage, as the plastic can transfer cold to the plant tissue and potentially cause more damage. Instead, use stakes or a frame to create a tent-like structure that keeps the material from weighing down the branches or touching the buds. These covers should be removed the following morning once temperatures rise above freezing to allow for light and air circulation.
Supplemental heat sources can be introduced beneath the coverings to raise the ambient temperature a few degrees. For smaller trees, this can be as simple as placing incandescent light bulbs (not LED) near the base, as the energy they use is released as heat. For slightly larger areas, large containers of water heated during the day and placed under the canopy will release stored heat slowly throughout the night.
Overhead misting or sprinkling is a high-risk, high-reward method used primarily by commercial growers. This technique relies on the principle of latent heat of fusion: as the water continuously sprayed onto the tree freezes, it releases heat that maintains the plant tissue temperature near 32°F. Application must be continuous from the start of the freeze until the ice begins to melt naturally the next morning. If the water application stops and the ice becomes cloudy, the protective effect is lost, causing the plant’s temperature to drop rapidly and leading to severe damage.
Assessing and Aiding Post-Freeze Recovery
Once the cold threat has completely passed and temperatures have normalized, carefully assess the extent of the damage. Flower buds and new growth are the most sensitive parts, and damage is confirmed by cutting open a few buds lengthwise and checking the interior tissue. Healthy tissue will appear green or white, while freeze-damaged tissue will be dark brown or black.
Resist the urge to immediately prune away any damaged limbs or branches, even if they appear blackened. The dead wood can still offer some protection to the underlying tissue from subsequent cold snaps or sun scald. It is best to wait until the tree begins its new growth in the spring, which clearly demarcates the dead wood from the living sections.
The tree will be under significant stress following a freeze event, so proper aftercare is beneficial. Provide a gentle, deep watering if the soil has dried out to support recovery efforts. Avoid applying high-nitrogen fertilizers immediately, as this encourages tender, new growth that would be vulnerable if another unexpected freeze occurs.