Recently we experienced the coldest weather in our area so far this season. Some areas were 32 degrees or less, while others were slightly warmer. How did your plants do? If you haven’t checked them, I suggest you do to look for any symptoms of cold damage. Symptoms to look for include:
- Obvious death, especially herbaceous types.
- Blackening or browning of foliage or spotting/streaking. Later hopefully these leaves will fall off. If not, there will be some die back of your plants.
- Limb or twig die back on shrubs or trees.
- Split bark and/or oozing of sap, particularly with azaleas and citrus.
- Flower buds fail to open or drop off.
- On trees and cold sensitive shrubs starting at the tip of a branch working backwards, check the color of cambium tissue just below the bark. If cambium is white or green your plant is ok. If brown/black , that portion of cambium is dead. I suggest using your finger nail or a small knife to check this out.
- Notes: Cold temperatures can affect all or just parts of a plant and symptoms may not show up till later in the spring.
- Temperatures do not have to be 32 degrees or less to damage plants. I’ve seen some affected by 35-36 degrees.
- By the way, now is a good time to also check your trees as they leaf out for any needed corrective pruning.
What to do if your plants are damaged by the cold?
- Don’t panic. Examine your plants to determine the extent of damage. You may find some damage; however, the prospects for survival may be brighter than you think.
- Don’t prune. Why? If done too soon it could force out new growth, which can be killed or seriously injured by any future cold weather.
- Wait and see what happens. Plant recovery is often very slow. Except for palm fronds, don’t remove any dead leaves. They can provide some protection and delays new growth. If the plant retains its dead leaves over a long period of time, this usually indicates that the plant has suffered some serious damage. Dead palm fronds should be removed to avoid possible bacterial infection.
- Maintain good cultural practices, especially watering. But don’t fertilize until after you see new growth developing.
What can you do to prevent or reduce cold damage?
- Maintain good culture, especially proper watering, pest control, pruning, and fertilizing, etc., at the proper times.
- Avoid any heavy/severe pruning after Oct 1st, especially if it has a high nitrogen number which is used to generate new growth.
- Know you plants cold hardiness.
- Avoid planting cold sensitive plants, especially tropicals. If you insist on planting them, do so in containers which can easily be moved into your home or garage prior to arrival of any cold spell. Remember, plants left outdoors in pots are more likely to be cold damaged than similar plants in the ground.
- Use cold hardy or native plants, which require little or no cold protection.
- During our winter months, keep an eye on weather forecasts, particularly when there is a high pressure zone and a full moon. That’s usually when we get cold damage. I personally also watch Southern Alabama’s weather. When they get cold, usually we will too in the next 24-48 hours, which gives you adequate time to prepare for the cold.
- If you cover your plants, I suggest doing at least a day before cold weather arrives. Don’t cover with sheets, plastic film, etc. Instead use something heavier or thicker, such as blankets, beach towels, old carpet remnants wrapped around a plant, and held in place by a black plastic garbage bag slipped over the top, or old thick walled packing/shipping boxes. Remember – you want to completely cover your plant – not just its top. If you have limited materials to cover your plants, it’s best to protect the base of the plant. The upper growth may be injured, but the plant should recover. As for frost cloth/bags, they only raise the temperature around the plant 4-8 degrees and should not touch any part of the plant. As a last resort, thoroughly water your plants, preferably a day before the cold weather arrives, and after the freeze has passed. Doing so will help keep heat in your soil and protect the roots and reduce desiccation of plant parts from drying out.
I’m often asked how long should I keep plants covered to protect them from the cold. I leave mine on until the freeze passes, (seldom more than 4-5 days here).
I’m also asked how low the temperature gets before plant damage occurs. My answer is that there are a lot of variables to consider such as size, type, how long it’s been planted, etc. Many herbaceous plants can be damaged at 35 degrees, especially if there is a cold wind blowing. Woody plants such as trees and shrubs, unless they are tropical, should have minimal damage. Citrus can withstand temperatures to the mid 20’s. Your lawn can withstand temperatures of 18-20 degrees.
If you have an in ground irrigation system, remember to turn it off the initial day of the expected freeze. Turn it back on after the freeze passes.
Click here for several IFAS publications on cold protection.