Minimum Temperatures for an Orange Tree

Site Selection

• Orange trees grow best in U.S. Department of Agriculture hardiness zones 9 and 10. Differences in slope, elevation, amount of hardscape nearby and the degree of previous frost exposure can influence the survival rates of orange trees in cold weather. Avoid planting orange trees within depressions of yards, because cold air tends to accumulate in these areas. Ideally, provide a southern exposure for orange trees. If possible, plant trees near walls or structures, which can provide some reflective heat and wind protection.

Cold Weather Impacts

• The twigs and leaves of frost-damaged orange trees will initially appear water-soaked. After a short period, these damaged portions of the tree will wither and darken in color. Fortunately, while a weak or young tree may die from frost, mature trees typically only sustain superficial damage. Frost may also damage fruit on trees, particularly fruit growing on the outer portions of the tree. Visually, the fruit may appear normal or slightly puffy; however, after only a few hours of freezing temperatures, ice crystals will form inside the peel of the fruit, which causes the juice vesicles to rupture. Unless this fruit is quickly removed from trees, it will become inedible.

Rehabilitation

• Avoid pruning orange trees immediately after a frost. Instead, allow a few weeks to pass, or ideally the return of spring, before making any cuts. Make pruning cuts slightly below where the cold-damaged wood starts. Occasionally, the whole tree will die from frost, leaving only the rootstock. Typically, the rootstock will send up new shoots that will eventually bear fruit, but this fruit will not resemble the fruit before the freeze. The appearance of leaves that are radically different than those on the rest of the tree, or a tree that produces excessive seedy and sour fruit, are indications that the original tree has died. Remove the rootstock and replant with a desired orange tree variety.

Other Considerations

• In general, duration of cold weather exposure has a more profound impact on orange trees than the actual minimum temperature. For example, several hours of freezing, 30-degree F temperatures will do more harm than an hour at 27 degrees F. In addition, timing of cold weather is also significant. Orange trees are better able to withstand freezing temperatures late in the winter season while they are fully dormant, than an early cold snap. If freezing temperatures occur in early winter while trees are still growing, trees are more likely to be seriously injured.