Citrus trees often become available for purchase in the fall and early winter. Since south Louisiana gardeners never know if a severe freeze will occur or not during winter, it is generally a good idea to wait until late February or early March to plant trees into the landscape. In the winter time, place container-grown trees in a sunny location and water regularly through the winter. Move them into a protected location when temperatures are predicted to go below 30 degrees. This allows you to keep your tree alive through winter even if temperatures in the teens occur.

If you do decide to plant a citrus tree in fall or winter, you must be prepared to provide protection should temperatures go below the mid to upper 20s. Gardeners who already have citrus trees growing in the landscape should plan when and how protection will be provided to the trees.

Factors that determine cold damage in citrus trees include age, variety and temperature. Age - Older, well-established citrus trees are more likely to survive severe cold weather than younger ones. Older trees have trunks that are more massive and able to live through freezes that would kill younger trees. Variety - Different types of citrus trees vary in their resistance to freeze injury. Following are citrus varieties ranging from the most freeze-tolerant to least freeze-tolerant: satsumas, kumquats, sour oranges, sweet oranges, grapefruits, lemons and limes. Temperature - Extent of damage depends on how cold it gets and how long it stays below freezing point. Satsumas and kumquats do not need protection until the temperature drops below 25 degrees and generally survive without protection if temperatures do not go below 20 degrees. Other types of citrus are more likely to be badly damaged by temperatures in the low 20s. Temperatures in the teens will severely damage or kill trees that are not protected. In addition, the longer temperatures stay below freezing, the more likely extensive damage or death will occur. If temperatures rise above freezing after just a few hours, damage is usually slight.

The weather prior to the freeze can make a big difference. Citrus trees that are gradually exposed to lower temperatures go through a process called hardening off, and there is a decrease in the freezing point of the tree tissues. Trees that are semi-dormant because they've been hardened off by earlier temperatures in the 40s and mid to upper 30s are less likely to be damaged.

Cultural practices that do not encourage late growth are important to the citrus tree's ability to harden off as temperatures drop. Avoid pruning and fertilizer applications after July.

PROTECTING CITRUS TREES - You can help reduce cold damage and ensure recovery to citrus by maintaining a healthy tree with a thick canopy of leaves. Weak trees under too much shade, those with insect or disease damage, or those with nutrient deficiencies are most severely damaged and the slowest to recover from freezes. In addition, keep the tree properly watered when freezing temperatures are predicted. You should plant citrus trees in protected areas of your landscape whenever possible. Southern exposures enclosed by hedges, fences or buildings on the north side offer protection from the north wind. When possible, plant citrus trees close to the house, but at least 5 or more feet away.

Protect trees planted in the ground that are not too large by constructing a simple frame over each tree and encasing them in one or two layers of plastic. The frame should hold the plastic from the foliage. When the day turns sunny and mild, you can vent or remove the plastic to prevent excessive heat from building up. In south Louisiana, this sort of protection is needed only on the few severely cold nights that occur here in December, January and February. But this can make a big difference because even one night of 15-degree temperature can destroy years of growth if not protected.

Care After Freeze Damage - Do not prune or cutback freeze-injured citrus trees until May. It is difficult to tell where re-growth will occur until the tree re-sprouts. Even then, new growth may collapse and die during summer. If the only new growth occurs from ground level or below the graft union (the graft union is often noticeable as a knob or swelling about foot or so above the ground), you should replace the tree. Citrus trees are grafted onto a rootstock that helps them grow better and makes them a little hardier, but the rootstock will not produce acceptable fruit. If new growth occurs from the above the graft union, it can be trained into a new tree.

Contact:
Ronald J. Nicholas
County Agent
St. Landry Parish
337-948-0561

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