The lemon tree, a subtropical member of the citrus family, thrives in warm, sunny climates and is highly vulnerable to cold damage. Lemon trees, including the widely popular Meyer lemon, are among the least cold-tolerant citrus varieties and require protection when temperatures drop below freezing. Temperatures below 27°F can cause significant damage to the plant’s leaves and wood, particularly if the cold spell is prolonged. A lemon tree’s survival depends on proactive preparation and strategic protection against hard frosts. The goal of winterization is to encourage a state of semi-dormancy that protects the tree’s vascular system until warmer weather returns.
Essential Preparations Before the Cold Arrives
A successful winter transition begins in the late fall, weeks before the first anticipated freeze, by encouraging the tree to “harden off.” This involves gradually reducing water and ceasing fertilization to slow down new, tender growth that is particularly susceptible to cold injury. Pruning should be kept minimal, focusing only on removing dead, damaged, or weak limbs, as heavy pruning encourages a flush of new, vulnerable growth.
For container trees that will be moved indoors, a mandatory pest inspection is necessary to prevent infestations inside the home. Common citrus pests like scale, aphids, and spider mites can thrive in the protected, dry conditions of a house. Thoroughly checking the underside of leaves and branch junctions should be followed by treatment with a targeted insecticidal soap or horticultural oil if pests are detected. Protection must be implemented before overnight temperatures consistently fall below 45°F to 50°F.
Protecting In-Ground Trees During Freezes
Trees planted directly into the ground require a multi-layered approach to insulation during cold snaps, as they cannot be moved. Protecting the trunk is a high priority, especially for young trees, which can be accomplished by wrapping the lower trunk with insulating material like burlap or specialized tree wrap. Alternatively, clean soil can be banked around the trunk for a foot or two, providing an excellent insulator that must be removed in the spring.
Root protection is achieved by applying a thick layer of organic mulch, such as straw or wood chips, spread several inches deep around the base of the tree. Keep the mulch several inches away from the trunk to prevent moisture buildup and potential rot. Prior to a freeze, thoroughly watering the ground is beneficial because moist soil absorbs and retains more heat than dry soil, radiating warmth back toward the tree canopy.
The canopy needs temporary covering when temperatures are forecast to drop below 27°F for more than a few hours. Lightweight frost cloth, blankets, or burlap should be draped over a temporary frame or the tree itself, extending to the ground to trap heat radiating from the soil. Supplemental heat can be added beneath the cover during severe freezes by stringing large-bulbed, incandescent Christmas lights—not LEDs—through the interior branches. The covers must be removed during the day if the temperature rises above freezing to allow for air circulation and prevent overheating.
Maintaining Container Trees Indoors
Bringing a lemon tree indoors presents a challenge, requiring precise adjustments to light, temperature, and moisture. The tree must be placed in the brightest possible location, ideally near a south-facing window, to receive maximum available sunlight. In northern latitudes or rooms with limited natural light, supplemental grow lights providing eight to twelve hours of illumination daily are necessary to prevent leaf drop and decline.
The ideal indoor temperature for overwintering a lemon tree is a cool, bright spot between 45°F and 55°F, which helps maintain a state of semi-dormancy. Standard household heating often causes low humidity, which is detrimental to citrus. Placing the pot on a saucer filled with pebbles and water can help raise localized humidity. The pot should rest on the pebbles, not directly in the water, to ensure proper drainage.
Watering frequency must be drastically reduced. The tree should only be watered when the top few inches of soil are completely dry to the touch to prevent root rot, which is a common killer of indoor citrus. Fertilization should be stopped entirely during the winter months, as the tree is not actively growing. Any new growth produced would be weak and highly susceptible to pest damage.