Citrus trees are popular in home gardens throughout California, Arizona, Texas and Florida. They don't grow reliably outdoors north of USDA plant hardiness zone 9B because they are cold tender. Limes, lemons and citron are the least cold hardy, while kumquats and deciduous non-edible oranges are the most cold hardy. Mature trees are better able to withstand freezes than young trees and those planted on a sloped, protected area sustain less damage than trees planted in low areas where cold temperatures gather. Does this Spark an idea?
Instructions
Preventative Measures
1. Plant cold hardy varieties, such as sour oranges (Meyer lemons), tangerines, grapefruit, sweet oranges, kumquats or 'Satsuma' mandarin if you live in an area prone to infrequent winter freezes between 20 to 25 degrees Fahrenheit. Lemon and lime trees suffer damage when temperatures drop below 29 degrees Fahrenheit.
2. Purchase trees grafted onto cold hardy root stock, if possible. The University of Arizona Extension recommends Trifoliate Orange, Flying Dragon, Cleopatra and Sour Orange as cold hardy root stocks.
3. Harden trees off in the fall by applying fertilizer with ample amounts of potassium (K) and phosphorus (P), with reduced nitrogen (N). Avoid pruning in the fall because pruning promotes new growth that's easily damaged by winter frosts.
4. Plant citrus trees in sunny, but protected locations near the south or southwestern side of a building. Citrus trees grown in urban areas where asphalt and cement warm the landscape are less prone to frost damage than those grown in rural areas.
Frost Protection
5. Wrap small citrus trees in burlap or blankets at night to conserve heat gained during the day. Wrap the trunks in cardboard or plastic wrap.
6. Place a shop light or a string of bulb-style Christmas lights in the tree with a covering to produce additional heat. Ensure that the light doesn't sit in water to avoid electrocution.
7. Water the ground to keep the soil evenly moist. Moist soils conserve heat better than dry soils, according to the University of Arizona Extension.
8. Run a sprinkler on the tree when temperatures dip, covering as much of the tree's canopy as possible. The water generates heat as it freezes and melts, allowing the tree's tissues to remain at 32 degrees Fahrenheit. Run the sprinkler continuously until temperatures rise above 37 degrees Fahrenheit.
9. Mound soil around the base of the tree to cover the graft union, identified by a lump or change in the color or texture of the bark. If the tree is killed by a freeze, it may regenerate from the trunk if the graft union is protected.
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