This weeks cold temperatures definitely got low enough to damage the tropical and subtropical plants in our landscapes. Freezing temperatures occur annually in north and central Florida but are rare for south Florida. Unfortunately, plants may not be the only casualties of the cold. In the days following 30 degree temperatures you may see dead frogs on palm trees and on the ground below. Last year when I came upon the frogs I would warm them in my palm and put them in the sun. When I returned they were gone and hopefully alright. The iguanas can also be killed by these cold temperatures and can be seen falling from the trees. This will be a good natural control of this invasive exotic. Some insects will die giving us a respite from that battle. I=m sure there were other mammals and birds that succumbed as well.
A lot of plants will seem fine in the days immediately following the freeze but in a week or so you will be noticing a lot of yellow leaves on your hibiscus, gardenias, and other sensitive plants. Not to worry. They will shed these yellow leaves and new ones should bud in their place.
Another type of winter injury is plant desiccation or drying out. This is characterized by burning of leaf margins or tips in mild cases and totally brown leaves in severe cases. Desiccation occurs when dry winds and solar radiation result in the loss of more water from the leaves than can be absorbed and transported by a cold or frozen root system. This damage will be evident where plants were exposed to the wind.
Tree canopy covers can reduce cold injury. Plants in shaded locations can go dormant earlier in the fall and remain dormant later in the spring. Tree canopies elevate minimum night temperatures under them by reducing radiant heat loss from the ground to the atmosphere. Plants that thrive in light shade usually display less winter desiccation than plants in full sun and so may have fared better.
If you have plants which received more severe damage, resist the urge to prune until new growth appears. You may be pruning away live wood and you will also encourage new tender growth which would make the plant more susceptible to further damage should we have another freeze, which is still a very real possibility. If the plant should fail to bud in the spring then prune back beyond the brown or discolored wood to wood that is free of injury. The plant will bud from the live wood.
Our warm season turf grasses like St. Augustine also suffered damage from the cold. Grass blades will turn brown and lawns will become somewhat dormant. It is not a good idea to mow brown, damaged grass until you begin to see growth again. Also, remember to reduce watering to once a week or less when temperatures are in the 50’s and 60’s during the day. Evaporation rates drop and the constant moisture creates great conditions for fungal growth on the weakened turf. To green the grass again in the cold weather apply a light feeding of ammonium sulfate.
Applying herbicides like Round up in the gardens or Atrizine for your lawn will not do much good in the cold as these products work by translocating throughout the weeds and cold or dying weeds are dormant and not transporting anything through their vascular systems. Wait to treat until they recover and begin growing again.
Your annual flowers may look wilted and discolored. If the damage is severe you may need to cut them back and apply a fungicide and fertilizer to bring them back to life. If the damage is minor just apply the fungicide and fertilizer and remove any rotten stems from the plants. I do not recommend fertilizing shrubs right now because of the new growth it will encourage.
Palm trees are also very susceptible to cold damage and may not show this damage until the new fronds (leaves) emerge six months to a year from now. Do not prune any green fronds even if they have some damage. The green fronds provide photosynthesis which is important to the health of the palm tree and will help in its recovery. You may prune away the dead, brown fronds but remember they act as a shield for the heart against the next cold spell so if you can tolerate the brown fronds I would recommend leaving them in place until warmer weather. Marco Island did not go below freezing so there is still time to apply a copper fungicide by drenching the heart with the fungicide where budding occurs. This treatment is more helpful when applied before a freeze rather than after. It looks like we may be in for a hard winter so this might be a good idea for your more precious palms. Be careful not to apply copper more than a couple of times a year as it can become toxic if used too often. The fungicide treatment will protect the damaged palm from bacteria which are always present at low levels in healthy palms. These bacteria can attack weakened palms by killing the bud and eventually the palm.
When warmer weather arrives the palms will begin to grow again and will often grow out of any problems caused by the cold. If the trunk tissue was damaged, you may not be so lucky. This will hinder the ability of the palm to transport water to the fronds. If some or all of the fronds collapse when the first warm weather arrives in spring after a winter freeze, it may indicate trunk damage. Unfortunately, this will result in the loss of the palm tree.
Tropical and subtropical plants can be used in our landscapes but they must be protected or you should be prepared to replace them when necessary. A combination of tender and hardy plants should be planted to prevent total devastation of your landscape by extremely cold weather. Remember, a healthy, well-fed plant will not suffer as much damage during a freeze. So be sure to follow a good fertilizer program all year to prepare your plants for winter. Or work on bringing your soil alive again.