When a cold snap threatens, don't forget that citrus trees need protection. Frosts usually occur when the weather is clear and calm. For a few hours overnight, temperatures drop below 20 F then rise above freezing as day returns. Frosts are temporary and different from freezes, which can last days, weeks or months. No citrus tree can withstand freezes, but many tolerate frosts providing they are protected.
Wrapping insulating materials around citrus tree trunks offers protection over winter. The best time of year for wrapping the trunks is late fall, but you can also wrap them on a dry, mild winter day. Suitable materials include palm fronds, cornstalks, fiberglass and cardboard. Start at the base of the tree, and wrap a layer two to four inches thick around the trunk up to the lowest branches. Tie twine around the material to hold it in place. When heavy rain is forecast add a layer of plastic to keep to keep the insulation dry. Don't forget to remove the plastic when the weather dries up.
Moist soil retains heat better than dry soil, and regularly watering citrus trees helps keep them frost free. When the soil is dry to a depth of one to two inches, water the ground under the trees' canopies, spraying the water evenly. Overwatering can do more harm than good, however, because citrus tree roots drown in soggy soil, so don't water so much that the ground becomes soggy.
Throwing a covering over citrus trees provides overnight protection from frosts. Larger trees may be too big to cover, but small trees benefit from this quick and easy solution. Spread burlap sacks, quilts, blankets or other large sheets over the trees' branches in the late afternoon or early evening before the temperature falls to freezing. In the morning when the temperature rises, remove the sheets so that the leaves aren't deprived of sunlight.
Lightly heating the air around citrus tree branches keeps frost at bay. Outdoor holiday lights and weather-proof incandescent light bulbs provide a surprising amount of heat. String holiday lights through citrus tree branches or fix a 100-watt light bulb at the center to protect one tree. When night falls, turn the lights on and leave them on until morning.
Grow citrus trees in areas of the garden where frosts rarely strike for long-term protection. Sunny spots sheltered from winds and next to brick walls are most likely to stay free of frosts. Bricks absorb heat from the sun during the day and radiate it at night, raising the local air temperature a few degrees. Slopes are also good for frost protection because cold air flows downward and away from the trees. Protecting citrus trees from frosts keeps them looking good and prevents damage to blooms and fruit, preserving your citrus crop. So when the weather forecast indicates frosty weather is on its way, step outside and see what you can do to keep your trees snug and warm.