Sunday, December 19, 2010

Cold Damage Identification and What to DO about it

The past month or so, I have made numerous blog postings about bringing in your plants and protecting them from the Winter weather. If you missed either of these postings, you can read it HERE and HERE .
Today I am going to talk to the people that, for one reason or another, didn't bring their plants in or try to protect them. They may have missed the weather report, forgot about their plants, or didn't want to take the time to do it and now their significant other is upset because the plant looks dead. There may be hope!
You will need to ask and answer a couple of questions: How cold was the temperature? How long was the plant exposed? What was the health of the plant before the damage?
First, let's take a quick look at what cold weather is and how it can affect plants. I know, duh, it's cold, they freeze! Well, just follow me for a minute.
The sun warms the soil surface during the day; the heat is then radiated into the cool atmosphere during the night. The coldest temperatures occur about daybreak.
Clouds at night can absorb and reflect heat back to the earth.
Calm, clear nights pose the greatest danger of frost since there is no wind to mix the ascending warm air with the descending cold air, and no clouds to radiate heat back to the soil.
Cold air settles downward, flowing like water,to the lowest point. Hot air rises.
The effects of temperature vary with plant species, stage of growth, age, general health and water content. Young, actively growing, flowering, and/or dehydrated plants tend to be most vulnerable.
Freezing temperatures damage plants by rupturing plant cells as ice crystals form and rapid changes in temperatures occur. Evergreen plants can suffer damage from blowing Winter winds and dry out when water is unavailable from ground that is frozen. Chilling injury can occur to many tropical plants although temperatures do not drop below 32 degrees.
The signs of cold damage can be confusing, since some damage may not be evident until months later. Leaves and tender shoots subjected to freezing temperatures or chilling damage appear water soaked and wilted. These tissues will usually turn black within a few hours or days. The tips of narrow-leaved evergreens, such as junipers, may turn uniformly brown. Broad-leaved evergreens, such as hollies, often have leaf burn along their edges. Less flowering is common during the following season.
One of the main things to remember is Do NOT prune frost-damaged, woody growth until the plant begins growing in the Spring. Pruning might stimulate new growth which would be vulnerable to late frosts. The frost damaged leaves and stems will continue to help trap warm air within the canopy. This is especially true in very large leaf type plants, such as Bananas. In addition, the damage is often not nearly as bad as it initially looked, new growth may come out of tissue that you thought was dead. Once the new growth starts in the Spring, you can prune out the dead wood.
A large, deep, crack running up and down the trunk of a tree or large shrub is known as a frost crack. The crack is usually on the South or Southwest side of the trunk, but can occur on any side. Young trees or older trees with smooth bark are the most susceptible.
Frost cracks occur when the sun warms the trunk in the Winter, causing tissues to rapidly expand or when clouds or buildings block the sun. At sunset the temperature of the trunk drops quickly to that of the surrounding air, and the trunk contracts. The outer part of the trunk cools and contracts faster than the inner tissues. This difference in contraction rates can cause the outer trunk to crack. You can usually eliminate this problem by wrapping the trunks with burlap or some other type of protection, not plastic, it needs to breathe. Start at the ground and work your way up to the first branch. Prevention is important, once the crack occurs, there is not much that can be done. Such frost cracks often close and callus over during the Summer, only to reopen in following Winters. This callusing and recracking may lead to the formation of large "frost ribs" on the side of affected trees. Something else to keep in mind, insects like to find places to hide and a large split open trunk is basically a "We'll keep the light on for you" sign. You could be looking at a major infestation. Frost cracks in trees are also ideal sites for the entrance of wood decaying organisms.
Desiccation, or drying out, is a particular problem on evergreen plants. This occurs when water is leaving the plant faster than it is being taken into the plant. During the Winter months desiccation can occur if the ground is frozen beyond the depth of the root system. If the Fall has been dry, there may not be enough ground moisture available for the plant. Water loss is greatest during windy, sunny conditions. This type of injury appears as discolored or burned evergreen needles or leaves.
After a killing cold some plants may be frozen back to the ground but lower buds and roots often survive. It can take these plants months to begin growth. Give them at least the Spring months to show signs of growth. I had a Clethera that did not regrow until Summer. I had just about given up on it but it showed me how persistent plants can be.
Okay, you have this plant that has lost all its leaves, looks naked and you are figuring it is a goner. Take a look at the bark or stem, is it black, shriveled or separated from the trunk? It’s most likely beyond help if it is. Don’t look just at the top but down at the base.
Next start high and scrape a small section of the bark. If you find brown at all keep moving lower until you find green, believe me you’ll know when you find it.
When you find an area of green, cut off everything above it, on that stem or branch. When you get done going over this you may have a plant that stands a chance of coming back. This really needs to wait until Spring though.
Remember, not only was the foliage, branches and stems exposed to the cold, so were the roots. No matter how hard you try the plant may not survive. The root damage may be so severe that you’ll be fighting an uphill battle.
As much as you may love your plant, you must be realistic, It may be too far gone!
I get teased all the time about my infatuation with what the weather is doing, what it is going to do and what it has done in the past. The best remedy is to keep your eyes on the weather, bring your plants in before the cold hits, and to grow things that are suited for your climate zone.
I hope everybody has a Very Merry Christmas!
Happy Growing!

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