This is very early for such cold weather. We had been enjoying beautiful weather in the 80’s when some very cold weather from the north dipped low enough to bring our temperatures into the 40’s and 50’s. I’m sure our plants are as confused as we are.
The cold weather came along with some very windy weather which causes a type of cold injury called plant desiccation or drying out. This causes leaf-tips to burn in mild cases and totally brown leaves in severe cases. Desiccation occurs when dry winds and solar radiation cause the loss of more water from the leaves than can be absorbed and transported by a cold or frozen root system. Plants located in the open and exposed to those cold, drying winds will be brown and void of leaves. Some plants may die from this but most will recover and new leaves will begin to emerge on the seemingly dead branches. Leaves on a lot of shrubs and trees will begin turning yellow and dropping after this kind of weather. Hibiscus, gardenias, bougainvillea, gumbo limbo trees, and most tropical and subtropical plants in our landscapes will have this reaction to the cold.
This will happen in a big way two to three weeks from now so remember this is when and why it happened! And also be sure not to over water your landscapes since the lower temperatures and fog can leave landscapes wet for longer periods of time causing disease to become a problem. Especially on cold damaged plants. Also remember lawns will be affected as well. St Augustine grass is a warm season grass which is susceptible to freeze damage. Blades will turn brown throughout otherwise healthy lawns. A treatment of fungicide will help protect healthy growth on plants from succumbing to disease problems. If you have patches of crab grass this is probably already brown from the previous cold weather and over watering will just fuel the growth of crab grass since it loves nothing better than a lot of water. And a lot of water will do nothing to turn it or cold damaged lawns and plants green again. When it is time to fertilize for spring, that will be the best way to green up your cold damaged landscapes. Wait until you are sure no more of this winter weather is coming this far south to fertilize. You don’t want to wake up plants causing tender new growth which can then be damaged with another freeze.
Our landscapes are already in a slight dormancy due to the lower temperatures earlier in the fall which causes a slight slowing of growth for tropical and subtropical plants. Tropical plants and annuals do not normally adapt to withstand temperatures below freezing and can be injured when temperatures reach below 50 degrees F. Fortunately, freezing temperatures are rare for South Florida and even more rare on coastal islands like Marco.
However, subtropical plants can, under the right conditions, acclimate to withstand freezing temperatures. The ability of plants to withstand freezing temperatures is affected by temperature fluctuations and day lengths before a freeze. A gradual decrease in temperatures helps plants to harden and withstand cold temperatures. We have not had enough periods of lower temperatures to hardened our plants. And if these cold temperatures are followed by periods of warmer temperatures that can de-acclimate plants resulting in budding or flowering making these plants more prone to freeze injury. Like I said our plants are as confused as we are with this weather.
Cold injury can occur to the entire plant or just some parts of the plant such as fruit, flowers, buds, leaves, trunks, stems or roots. The fruit and roots are most vulnerable to cold damage. Especially roots of container plants. This damage won’t usually become evident until the plant is stressed by higher temperatures in the spring.
Steps, from selection of proper planting sites to good cultural practices, can help acclimate plants to cold temperatures and protect them from temperature extremes.
Site selection. Temperatures can fluctuate from one location to another in most yards. Thus, microclimates should be considered when choosing the planting site for cold sensitive plants. Tender plants should be planted in areas with good air flow never in low areas where cold air settles. Arranging plants, fences and other barriers to help protect plants from the cold winds of advective freezes can help. Avoid poorly drained soils which will result in shallow, weak root systems making plants more susceptible to cold damage.
Plant nutrition. Properly fertilized plants will tolerate cold temperatures better and recover from injury faster than weak, underfed plants. That is why it is so important to fertilize in the fall before the cold weather of winter arrives. After the cold weather arrives plants will not “take up” or use fertilizer applied due to the dormancy.
Shading. Tree canopy covers can reduce cold injury caused by radiation freezes. Canopies can raise night temperatures under them by reducing heat loss into the atmosphere. Early morning sun after a freeze can cause bark splitting on plants and the shade can help prevent this problem. However, be sure shrubs planted in the shade are shade tolerant or you will end up with sickly plants which will also be more vulnerable to cold injury.
Watering your landscape before a freeze can help because a wet soil will absorb more solar radiation than dry soil and will re-radiate this heat during the night. However, it is not good to saturate soil for prolonged periods as this could cause root damage.
Avoid late fall pruning which can result in budding and a new flush of growth. This tender, new growth is more susceptible to cold injury. This is why they tell you not to do any hard pruning after October 15th.
Keep your plants healthy. Plants weakened by insects or diseases are not as resistant to the cold. Inspect your plants regularly and treat them as necessary to avoid serious problems.
Potted plants that can be moved indoors for a freeze should be. Larger containers that must be left out should be pushed together and mulched to reduce heat loss from the tops and sides of the containers. This will help protect the roots. The soil should be moist not dry. Be careful not to leave canopies of plants together for extended periods as this could cause leaf and stem damage.
Radiant heat from the soil will protect low growing plants on cold, calm nights. Taller plants do not enjoy this benefit as much because of their distance from the soil. Mulches help to reduce heat loss from the soil helping to protect root systems.
Covering your plants should be done carefully. Covers that extend to the ground and are not in contact with the foliage can trap radiant heat from the soil and plant. Foliage in contact with the cover can be injured because the heat transfers from the foliage to the colder cover and is lost. You can purchase special “frost blankets” from the local garden center or use old sheets or blankets. Plastic is not recommended but if it is all you have, be sure to remove it promptly the next day to avoid burning your plants with trapped solar radiation.
Marco Island is usually spared the severe damage suffered by the inland communities due to our close proximity to the water. Just remember to be prepared as it does happen and when it does we can lose a lot of our more tropical plants. Winter has not even begun. Serious freezing weather can just as easily cross over the bridge so prepare your landscapes for it now.