Lemon trees photosynthesize at peak levels when temperatures remain steady around 86 degrees Fahrenheit. However, many regions where lemons grow in U.S. Department of Agriculture plant hardiness zones 8 through 10, are subject to overnight frosts which impedes lemon tree growth. Unlike a freeze, a frost is a short duration of sub-freezing temperatures. If your lemon tree is exposed to a frost, a number of strategies may be employed to ensure its continued health.
Cold Temperature Damage
Frost damage begins with flowers dying, along with any immature fruits on the limbs, at temperatures of about 29 F. Large fruits do not escape frost damage either, since the internal juices begin to crystallize and expand the fruit until it breaks apart between 28 and 31 F. Leaves fall off the tree when temperatures reach approximately 24 F. If your tree continues to bear a frost down to 20 F, the bark becomes injured, since fluids within the tree cannot move and begin to expand from within.
After a frost, you must be diligent about evaluating your lemon tree to avoid further damage from disease. Any obvious cracking along the fruits' skin indicates damage and you need to remove the lemon from the tree so that it does not become a haven for fungus and mold. Fruits that drop to the ground also need to be removed to keep the surrounding area free of pests and pathogens. After a week passes, any healthy fruits on the tree should remain firm. Soft and squishy fruits need immediate removal, but you may juice these fruits, if desired, since their health was not compromised with skin damage.
It is tempting to begin immediate limb removal after a frost, but it is possible that the tree is not as badly damaged as first thought. If you wait until late spring and early summer, the bright light helps you evaluate the entire lemon tree canopy so that it successfully survives another growing season. At this point, you must cut any limbs off, just below the injured area, if they show signs of frost damage. However, any obviously broken or hanging limbs need to be pruned immediately to preserve the tree's stability and to keep everyone safe below the canopy.
After surviving a frost, you need to prepare your tree if frost threatens the area again, to avoid future extensive damage. Stringing a light bulb, or set of bulbs, near the tree helps generate some heat in the area, although it is minimal. Cardboard or palm fronds are perfect insulators for your lemon tree's trunk. If you wrap the tree with warm material, it acts as a winter coat for the citrus. Another trick for frost damage prevention is keeping the soil moist. As moisture evaporates, it generates some heat that helps your tree remain warm during a frost.
- Purdue University: Lemon
- University of Florida IFAS Extension: Lemon Growing in the Florida Home Landscape
- University of California, Davis: Frost Protection for Citrus and Other Subtropicals
- University of Arizona: Protecting a Citrus Tree from Cold
- New South Wales Department of Primary Industries: Growing Lemons in Australia- A Production Manual - Readers’ Note
- Hemera Technologies/Photos.com/Getty Images