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Citrus Trees in a Freeze

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Information on Citrus & Cold Weather/Acquired from LSU Ag Center
Protection of citrus trees becomes important when severe freezes occur. Citrus types vary in their tolerance of cold. For example, Satsumas are the most cold hardy, and do not need protection until temperatures approach 20 degrees. Lemons, limes & oranges generally need to be protected when temperatures get below 26 degrees. In order from most to least cold hardy:
Satsuma, kumquat, orange, grapefruit, lemon, and lime.
The length of time citrus trees are exposed to freezing temperatures makes a difference. If exposure is more than 24-36 hours, damage can be devastating. If the exposure time is less than that, damage can be light.
All ripe fruit should be harvested prior to a freeze. Temperatures cold enough will damage existing fruit as well. Note: it takes temperatures in the mid-low 20s for 5-10 hours to freeze the fruit.
The hardiness will increase in more mature citrus trees, and trees with larger, denser canopies can trap more heat and tolerate more cold.
The best way to lessen cold damage to citrus is to maintain healthy plants. Do not prune or fertilize in late summer or fall. Pay attention to weak trees showing signs of disease, insect damage or nutritional deficiencies because they are the ones most severely damaged and are the slowest to recover.
Steps to reduce freeze damage:
1. Clean cultivation under the canopy prior to winter.
2. For trees too large to cover, banking the lower trunk with soil or using tree wraps of bubble wrap, Styrofoam or rubber foam will help prevent cold damage to the trunk. This must be done before the first freeze, and can stay on throughout winter. Prior to covering, trunks should be treated with a copper fungicide to prevent root rot.
3. If the weather prior to a freeze has been dry, water the soil beneath the citrus tree well in advance of a freeze approaching. Good soil moisture acts as a cold buffer, but watering too near the freeze timeframe could result in evaporation and colder temperatures in the tree.
4. If pruning is needed, it should be done in the spring to allow the new growth to mature before winter. Do not prune in late summer or fall. Cuts should be made at the branch crotches leaving no stubs.
5. Fertilizer should be applied to citrus trees in late January or early February.
6. Oil sprays to control insects and mites should not be used later than mid-August.
7. To protect a small single tree, construct a simple frame over it with one or two layers of translucent plastic. The frame and cover can stay in place indefinitely, but will need to be vented.