The lemon tree (Citrus limon) is a subtropical evergreen plant that thrives in warm climates, making winter its most challenging season. Survival depends entirely on the specific climate zone and the degree of protection provided. While lemons do not enter true dormancy, they slow growth in response to cooler temperatures, helping them tolerate some cold exposure. The primary concern is the duration of the cold event and the tree’s overall health entering the winter months.
The Critical Temperature Thresholds
Lemon trees are among the least cold-hardy citrus varieties, alongside limes and citrons. The danger zone for foliage and fruit begins when temperatures fall to 32°F (0°C). Most varieties sustain leaf and twig damage when exposed to temperatures in the mid to high 20s Fahrenheit (around -4°C to -2°C) for several hours. Wood damage occurs when temperatures drop below 26°F (-3°C) for an extended period, and severe, lethal damage to the trunk and scaffold branches occurs closer to 20°F (-6°C). Young trees, those under four years old, are more susceptible to injury than mature trees because their wood has not fully hardened.
Protecting In-Ground Trees
Preparation for in-ground trees focuses on insulating the soil and providing temporary shelter during cold snaps. Deeply watering the soil before a predicted freeze is helpful, as moist soil holds and radiates more heat than dry soil. Removing grass or mulch underneath the canopy also allows the soil to absorb and release warmth more effectively.
The trunk, especially on young trees, should be protected by banking clean soil up around the base, reaching about a foot high, or by wrapping it with insulating materials like burlap or cardboard. For the canopy, temporary covers such as frost cloth or sheets should be draped over the entire tree, extending to the ground to trap escaping heat. Incandescent light bulbs or specialized heating cables placed beneath the cover can provide extra warmth on cold nights.
Overwintering Potted Lemon Trees Indoors
Gardeners in colder climates move container-grown lemon trees indoors for the winter, transitioning them to semi-dormancy to conserve energy. An ideal indoor temperature range is between 50°F and 60°F (10°C to 15°C), which is cool enough to slow growth but warm enough to prevent cold shock. Placing the tree in a south-facing window is beneficial, but supplemental grow lights are often needed to ensure the tree receives the minimum 6 to 8 hours of light required to prevent leaf drop. Indoor heating systems drastically lower humidity, which stresses the tree and leads to leaf loss.
To combat this, a cool-mist humidifier or a pebble tray filled with water can raise the local humidity level. Watering frequency must be reduced, allowing the top inch or two of soil to dry completely between waterings, and fertilizer should be suspended until spring. Before bringing the tree inside, check the foliage and soil thoroughly for pests like scale and aphids, which multiply quickly indoors.
Identifying and Treating Cold Damage
After a freeze event, wait before pruning, as the full extent of the damage is not immediately clear. Visual signs of freeze injury include curled, tan-to-brown leaves and dark, water-soaked areas. Wood damage manifests as split bark or branches that turn black. Pruning should be delayed until late spring or early summer after the tree has put out a full flush of new growth. Waiting allows the gardener to accurately determine which wood is dead. During recovery, reduce irrigation since the defoliated tree requires less water, and minimize fertilization to avoid stimulating tender growth vulnerable to late frost.