Lemon trees thrive in temperate and tropical climates and are easily damaged by cold and frost. Lemons will experience stress and some cold damage when exposed to temperatures below 30 degrees Fahrenheit--and temperatures below 25 degrees Fahrenheit can be deadly. Physically wrapping the trees when cold and frost are anticipated and providing a heat source can protect the tree during this period and prevent harvest-related losses and tissue death.
Drape one or more thick but lightweight blankets, quilts, old duvets or canvas tarps over the lemon tree and weight the edges to the ground with rocks or wood, plastic or metal stakes. Tape the seams with duct tape if needed to keep them closed and prevent gaping or intrusions from wind.
Slide one or two burlap sacks over the top of small, young or dwarf lemon trees and tie the sack around the trunk under the canopy with string or twine.
Erect a lumber frame over very large lemon trees to hold the weight of multiple blankets and/or tarps without weighing the tree canopy down and risking branch damage. Nail together standard vertical lumber, such as two-by-fours, to make a basic frame at least as tall as the tree. Set four posts as the legs of the frame and nail header two-by-fours at the top edge of each post, connecting them to create a sturdy open and freestanding frame.
Drape the coverings over the frame and weight the edges with stakes or stones. Tape the edges of overlapping blankets to keep them closed if need be.
Add an outdoor safe light under the blankets to serve as a heat source overnight. Wrap holiday lights around the lemon tree trunk and branches and keep on all night and into the early morning. Alternatively, clip or hang an incandescent shop light fixture in the tree canopy, being careful not to leave the bulb itself resting against the tree foliage or branches.
Leave the wrapping secured in place until at least the sun is fully up in the morning, temperatures have warmed and the frost has dissipated.