Freezing temperatures may arrive in South Florida over the weekend. Most vegetables – lettuce, broccoli, herbs, cauliflower – should do fine. You might see leaf damage on plants like basil. Some backyard gardeners like to cover sensitive crops with sheets (use stakes to hold them above the plants).
But tropical fruit trees are a different story. At the Tropical Research and Education Center (TREC) in Homestead, Dr. Jonathan Crane advises running irrigation systems now for 2-3 hours to get the soil wet. “The wet soil will absorb the sunlight Thursday and Friday/Saturday and re-radiate the stored heat back into the grove at night,” he said in an advisory for growers, adding it’ll be too late for the pre-freeze irrigation if we get windy by Friday. “Why? Because the wind will cause evaporative cooling and make the environment cooler.”
Crane notes that the National Weather Service has forecast 36F for South Florida (Miami-Dade County) on Jan. 29-31 (Saturday night/Monday morning). However, it may get colder than that because their temperature predictions are from urban/airport areas and there will be at least two days of low temperatures (usually colder the second night). You can watch Dr. Crane’s detailed video here.
Jeff Wasielewski of the Extension office offers these tips for protecting your fruit trees:
Ultra-tropicals, like rambutans, pulsans and mangosteens will generally not survive a freeze, even when you use cold protection. That’s why they’re only grown in greenhouses or protected areas. Breadfruit and guanábanas (soursops) will get damaged by temperatures above freezing, but have fared better in the past years due to warmer temperatures. Most other subtropical fruit trees like mangos, avocados, canistel, lychee, longans and mameys will survive a prolonged freeze if they’re protected using the methods described below.
Several factors, besides the species of fruit, can help predict whether your trees may be in danger when cold temperatures hit. If your tree is planted in a low area, cold air will pool there, and temperatures will be lower in that spot. Healthy trees that are dormant will fare better than trees that are putting out new growth. Trees are more likely to be dormant if they haven’t been fertilized or pruned going into the winter. And older trees will survive a freeze better than younger trees.
If a freeze is on its way, there are a few ways you can protect your trees:
• First, soak the area around the tree with water several days before the freeze hits, not the day of the freeze. The water will hold and release heat during the freeze.
• You can also wrap the trunks of your trees with insulation and tie it in place. Have a thermometer and monitor it through the night.
• Start irrigation before the temperature hits 32°F, around 36°F, and it must hit the trunk or cover as much of the plant as possible. Water releases some heat as it is pulled from the ground and when it turns from water to ice. This heat is just enough to encase the tree in ice, and keep it at 31-32°F. This will keep most subtropical fruit trees alive.
• Don’t turn off the water until the threat of the freeze has passed and the temperature hits 40°F.
After a freeze, you may see some bark splitting or twig death. You may also see leaf wilting or browning. The leaves may die and stay on the tree or drop off. If they drop off, this is a good sign that the branches are alive and active.
Don’t prune right after a freeze. It may be tempting to prune out dead areas of your tree, but you might cut into the live wood. The dead leaves may also protect the rest of the tree if there’s a second freeze. Don’t prune until two to six months after winter has passed. If you have significant leaf damage, don’t irrigate at your normal rate because the trees will not be able to take up the same amount of water.
