Palms are one of the key elements of many tropical landscapes, and they deserve special attention during a cold spell. Cold weather can weaken the palm, making it more vulnerable to disease, and frost and freezing temperatures can kill plant tissues, reducing water conduction in the trunk for years.
After a frost, remove damaged portions of leaves, retaining as much of each leaf as possible. In general, if any green remains, leave the frond; it's helping the tree make food. Even completely brown fronds provide some insulation, so wait until spring to prune. Immediately after pruning, spray the palms with a copper fungicide, covering the damaged tissue and healthy bud. (Note: This is recommended only for palms that do not bear edible fruit.) Repeat the copper spray seven to 10 days after the first treatment, but don't spray more than twice. Too much copper could poison the plant.
Don't give up if cold damage is severe and the spear leaf (the center youngest leaf, which has not unfolded) becomes loose and pulls out easily. There is still a chance of recovery. Once the spear leaf is removed, slit or puncture the collar of sheathing leaf bases to allow water to drain away from the bud. Take care not to injure the solid, undamaged tissue of the bud. Remove as much dead and decaying tissue around the bud as possible so it can dry. Drench the bud with a copper fungicide using the force of the sprayer to clean out around the bud. Follow up seven to 10 days later with another fungicide application.
Warm weather will promote growth and help the palm recover. If healthy leaves are present, or as soon as new leaves emerge, apply a soluble trace element nutrient mix plus a spreader sticker additive to the leaves monthly until new growth is established.
Palms should be fertilized four times a year, and a well-fertilized, healthy palm will have a better chance of surviving a cold spell. Use only an 8-2-12-4 Mg fertilizer with micronutrients. The nitrogen, potassium and magnesium should be in controlled-release form, and the micronutrients should be in a water-soluble (sulfate) form. This is the only fertilizer that should be used within 50 feet of any palm.
Watch severely damaged palms carefully in the spring and summer. Damaged leaves may not be seen for six months to a year after a freeze. Palms will usually outgrow these damaged leaves over time. If there is a sudden collapse of the leaves or crown, there is nothing to be done and the palm usually must be replaced.
Jane V. Morse is an extension agent in the commercial horticulture department of the Pinellas County Extension Office. Information from the UF/IFAS publication "Treating Cold-Damaged Palms" and the book "Ornamental Palm Horticulture" by Timothy Broschat and Alan Meerow (University Press of Florida, 2000) was used in this report.