Overwintering Citrus | Gardening

Citrus trees are evergreen, not deciduous. They are able to slow their growth during hot and cold temperatures but do not go dormant.

Evergreens need light and water year round. Citrus requires high levels of light, even in winter, to survive the cold and produce quality fruit.

Some citrus are hardier than others. Know your cultivar. Meyer lemon, for example, is considered the most cold-tolerant citrus variety. If you dream of growing a Key lime tree, know that the cultivar is very sensitive to cold.

Several factors determine whether a citrus plant will be damaged by freezing temperatures:

The duration of freeze affects the degree of injury to the plants’ fruit, leaves and wood. Generally fruits freeze at 26 – 28 degrees F. Temperatures in mid to high 20s can damage or kill plants.

An older plant withstands lower temperatures better than a young plant. As trees age they become more cold hardy (while fruit becomes sweeter). A damaging temperature can be five to six degrees lower for a cold hardened plant.

Dry plants can survive a two to four degree lower temperature than wet plants.

Moist soil better protects roots because it absorbs more heat during the day than dry soil

Windy cold is more damaging to leaves than still cold.

In Ground Plants

In a severe freeze citrus needs protective cover. Cover your tree with blankets (no plastic) and remember to remove them in the morning. One or two incandescent lightbulbs under the cover helps keep the temperature above freezing.

Every part of a citrus tree is sensitive to cold. Consider banking young trees in winter for their first three to five years. Banking is a process whereby surrounding soil is raked and mounded to cover the first bud union and lower trunk of the tree.

Running your irrigation system to protect citrus is an option for short and sudden drops in temperature. Start when the temperature drops below 32 degrees F, one quarter inch per hour of water must cover leaves branches and trunk until the temperature rises above 32 degrees. The layer of ice that accumulates on the tree prevents it from freezing. Be aware you may need to support tree limbs to bear the weight of the ice.

Roots are better insulated in the ground than in a pot. If you have a potted citrus too large to move, cover it to the ground with a fabric (never plastic) blanket. Place an incandescent spotlight or a couple of caged incandescent bulbs under the drape. Secure the bottom of the cloth with bricks or other heavy anchors. That will add several degrees to the enclosure. As soon as the temperature rises above freezing turn off the light and remove the cover.

Container Plants

If your citrus grows in a pot put it on a dolly and wheel it into a garage or other enclosure to escape frost and freezing temperatures. Remember that citrus needs as much light as possible during winter’s low light. Don’t stash your tree in the dim back of your garage until spring. Avoid overwintering citrus indoors in dry heat; citrus need humidity.

Leave your citrus outside as long as possible. Move it up against the house as the weather starts to cool, then into the garage or cool sunroom for frosty nights. Take advantage of warm periods and move plants back outside. An unheated garage should provide adequate protection for most of the winter. If the outside temperature drops below 25 degrees potted citrus should be moved to a cool but heated area. Indoors watch for fungus gnats, spider mites and scale insects.

As the light level decreases plants respond by dropping some leaves. Citrus also sheds leaves when over watered. Let soil dry out between watering.

A major temperature difference between the roots and the leaves occurs when a pot sits on a cold floor in a warm room. The cold roots function more slowly than the warmer leaves. The disparity stresses citrus causing leaf drop. Solve the problem by placing the pot on a dolly with castors to allow airflow under the pot or put the pot on a piece of Styrofoam for insulation.

Overwintering citrus in our climate is quite manageable. Looking ahead, the milder the winter the less protection citrus may need.

This story was originally published December 10, 2016 at 5:22 AM with the headline "Overwintering Citrus | Gardening."