COLD PROTECTION DESIGNS

MINIGREENHOUSES are the most elaborate and time-consuming but offer best and complete protection for the plant. Usually a frame is constructed around the plant and covered with a transparent plastic. Artificial heat is added i.e. heating wires/pads, electrical or gas stoves, light bulbs or even Xmas-lights. Be aware that whatever part of a leave touches the plastic will get exposed to the outside temperatures and will most likely turn brown. If the winter sun starts to 'bake' too much add a door which can be shut during the night or add a screen. Problems: Theres a good chance that much humidity and heat attracts fungus - prevent or eliminate with a fungicide. Animals find a comfortable warm shelter i.e. ants or even rodents - exterminate these pests immediately. Also, a minigreenhouse runs remote a chance of carbon-dioxide starvation - just have the air exchange several times a week. (click here for Greenhouse Links by the Gardening Launch Pad and the Greenhouse Forum, Electronic Book on Greenouse Gardening).

KEROSENE HEATER if you have a several tender plants or even a whole field where it becomes impractical to build a minigreenhouse around each plant, you have to use more drastic methods. One method, pioneered by citrus growers is to place a number of kerosene heaters to increase the temperature of the field. These heaters come in many shapes and sizes. The problem with this method is it's dangerous and you might set your plants or even yourself on fire if you are not careful. Plus you need to stay up during a freezing night and observe your heaters. This definitely is effective but limited to your own taste of adrenalin and sleep deprivation.

COLD FRAMES are used for the long-term, installed for the whole cold season. They come in many different designs but have at least one of the following features in common: (1) Protect from wind, (2) collect the sun's heat and increase the temperature, (3) keep the central growth bud dry, so no ice will form, (4) protect from heat radiation.
The following examples provide variations to accomplish the above features:

• Coldframe I: Just like a Minigreenhouse but lacks artificial heat. Unless you plan to add artificial heat this method makes limited sense because a temperature increase of only one or two degrees can be expected during minimum temperatures. It will definitely take care of (1),(2), (3), and (4). However, it bears all the problems associated with a greenhouse due to it's completely 'enclosed' nature.
• Coldframe II: Construction just like the coldframe I but leave a gap of a few inches between the ground and the plastic. This will do (1), (2), (3), and (4). However, it will not increase the night's minimum temperature. A plus for this design: it bears no problem with fungus or pests.
• Tripod: Three stakes (or more) around the palm's stemm to support a plastic roof will keep rain from touching the sprear, see (3). This will not increase the night's minimum temperature. No problem with fungus or pests either.
• A simple Plastic Cone with an opening on top is good for very small plants and will do (1) and (2). However it will not increase the night's minimum temperature. Usually no problem with fungus or pests. Suitable mostly for seedlings. Anker it to the ground so the wind wont blow it away. I use a u-shaped piece of wire and 'staple' the cone into the ground.

WRAPPINGS can be installed for only one night when a cold front hits or are left for the whole cold season. These are more effective than the open coldframes because a wrapping is in close contact with the part of the palm you want to protect. However, this method has a very high risk of fungus, pests, and light and even air deprevation. Most importanly the wrapping can physically destroy parts of the plant due to the pressure inflicted i.e. leaves. The following are the main designs used:

• Permanent Artificially-Heated Whole-Plant Wrapping: First, cut off all lower leaves until you can fold them all up around the spear (NOTE: This is the most damaging to the leaves. Even if this is done very carefully the leaves will always suffer. Feather shaped leaves survive this torture better but for fans, wrapping is very questionable and not recomended). Fix the leaves by wrapping a string around them very gently. I use several omega-shaped pieces of a strong wire. Basically, these are rings with an opening. Each ending is shaped to a small U. When the Us are hooked together you have a perfect circular wire of about 2 feet diameter. This allows me to tie the foliage together rather quickly while avoiding the dangerous armoring of many palms.
  Now, take a heating wire/pad or x-mas lights and wrap it around the palm's stem and foliage. For heating wires/pads; try to have the temperature sensor on top of the plant where the coldest temperatures are expected. Then use a respiring, non-transparent material i.e. burlap, grocery-paper bags etc. (do not use any plastic which will suffocate the plant). Make sure there are no openings in the wrapping because it needs to protect from winds. Any opening will inhibit some of the artificial heat. Use tape to first fix the sheets around the plant, then take a string to permantently fix the whole wrapping. This will prevent the wind from blowing it away eventually. If the plug of your heating wire/pad is on top of the plant, you can attach the electrical cord on the outside of the wrapping at the same time. Leave a generous opening in the wrapping on the very top to prevent fungus. This also gives the palm some light and space to grow. Add a thick layer of mulch that covers the wrapping by a few inches. Add a granular pesticide to the mulch to keep ants away. Problems: most damaging to foliage. Need to check periodically for openings in wrapping, electrical power, fungus, and pests.
  
• Permanent Artificially-Heated Stem Wrapping: This is almost the same as the whole-plant wrapping except for the step where the foliage is tied up around the spear; Start with wrapping the heating wire or x-mas lights around the stem and spear keeping the temperature sensor on top. Then use a respiring, non-transparent material i.e. burlap, strong paper etc. to wrap it all up (stem and spear only) avoiding openings. Fix it permanently with a string. Add a thick layer of mulch and add a granular a pesticide for ants. This design will not damage the leaves due to pressure or fungus. It will protect the central growth bud from damage. If you have a recently planted hardy species this might be the best way to protect. Older leaves usually survive anyway but the plant is prone to lose the spear in spring i.e. Trachycarpus, Butia etc. Again, you need to check periodically for openings in wrapping, electrical power, fungus, and pests.
• Permanent Non-Heated Whole-Plant Wrapping: As a long-term, seasonal protection, this makes absolutely no sense because the gain of two degrees will not offset the physical abuse of the foliage and the risk to fall prey to fungus and pests.
• Temporary Wrapping: This is a short-term wrapping installed for a few days at most when a damaging cold front hits. Here, almost everything goes as to materials for wrapping or artificial heat. See above examples for different designs. Most noteworthy is the Plain Plastic Wrap which aims to block freezing wind. IMPORTANT: Remove any transparent wrapping during morning hours before the sun hits or you will bake the foliage. You can leave the non-plastic materials installed for the day and cover it back up with the plastic for the next night in the evening. There is absolutely no risk for fungus or pests due to the short-term nature of this protection. However, physical foliage damage may occur.

THE CAGE: Most useful for plants with a subterranean growth bud i.e. bananas. This method aims to protect most of the stems of a banana plant. First, in fall start by chopping all stems about 2 to 3 feet from the ground when they are still undamaged from early freezes. Now get an organic medium with a lot of air in it i.e. old leaves and accumulate them in a pile around and over the remaining, chopped-off stems. To keep the leaves in place most put a chicken wire fence around the pile - that's why this is called the 'cage' design. The very thick layer and air pockets in the organic medium keep freezing temperatures from reaching the stems and corms. In spring, when temperatures rise the center of the stems will shoot and produce new leaves very rapidly. If you let the stem freeze, a whole new shoot needs to develop first in spring. So, the cage method saves about a month or two of growth for the next season. Make sure to remove all of the old leaves in spring and replace them with a small layer of a rich soil mix. This method might be useful to palms without arial stems and which are not prone to fungus i.e. Sabal minor. (See a more detailed descripton and a picture in action).

THE BOX: A simple version of the cage method; For short freezes and relatively small plants, i.e. cycads, a cardboard box is placed over the plant and filled with leaves, newspapers or other insulating material. In addition, also manure is used to temporarily increase the temperature.

THE BLANKET: Use a blanket for protecting medium to small sized plants during short freezes. Mostly wool blankets to clear plastic is used. If you just protect the plants over night everything that traps the heat will do - just remember to remove it in the morning, especially the non-perspiring plastic. If you have several nights of freezing temperatures and want to leave the cover in place you need to be a little more choosy about the material, so the plants wont cook during a sunny day. One product is the Park's Plant Protector recommended by Tamar Myers in her recent article in Rhapidophyllum V5#3pp12-3. 'This item is an ultra-lightweight, porous material that lets water and sun through, but traps 3 or 4 degrees of heat. It is excellent to use as a cover on those palms which can tolerate some freezing, but not the formation of frost directly on their leaves i.e. Sabal Riverside'. Get it from the Park Seed Company. Prices are around $12 for a 71"x30' sheet and $50 for a 35'x35' sheet.
John Spaulding of Seattle, member of the Pacific Northwest Palm & Exotic Plant Society, drapes a protective covering over his palms called REEMAY CROP COVER, a polyesther fibre used by the tree fruit industry to protect against winter frost. It is sold in rolls 67" by 128 ft (actually 134" wide but folded in half). It is sold by Teufel Nursery out of Portland Oregon and perhaps others. He recommends the "breathing" variety that allows for the exchange of air, necessary to avoid mildew and fungal attack.

WATER/SPRINKLER:
Water BEFORE A Freeze: When a freeze only lasts for a few hours: Try turning on the sprinkler and water(soak) your yard during the warmest afternoon hours in order to capture some of the day's heat. During the night a short radiation freeze will not have much of an impact since the wet soil has stored some heat and will release it during the cold night. However, this artificial microclimate will only hold for mild freezes and only for a few hours.
          NOTE: This technique is most efficient if the soil has poor drainage i.e. lots of clay. For soils that drain very easily i.e. lots of sand etc. the water will not stay in the upper region of the soil long enough to warm and radiate heat during the night-freeze when it is needed.

Water DURING A Freeze: If the freeze is worse than expected you can still use your sprinkler during the freeze: For example, citrus growers turn on their sprinkler systems as a last resort. When liquid water freezes, it gives off heat. This heat warms the area. The sugar acts as antifreeze in the flowers and fruits so these parts will take a degree or two colder. However, growers also must keep watering until the sun melts the ice. Otherwise the ice layer will grab heat from the plant as it thaws.
          NOTE: Watering during a freeze can be very damaging to the growth center of several palms i.e. Phoenix, Brahea, Trithrinax and many other genera that rather like to have their heads in dry air during a freeze. If water enters the growth center, ice crystals forming around the growth bud may cause extensive damage and can result in the death of the palm. So, cover the spear with aluminum foil or a plastic to keep it dry or direct your sprinkler away from such a palm's crown.
          In addition, creating a wet environment during a freeze can damage certain species which are used to very arid environments i.e. Brahea armata. A freeze stresses a palm the same way as a drought. That is why many drought resistant species are also able to survive hard freezes in a desert situation. If you, however, add water before and during a freeze such a plant is fooled into believing there is no imminent stress and it may not activate its own natural defences during the actual freeze.

MULCHING: Don't underestimate the effectiveness of a good layer of mulch about 3 to 6" thick. Most fine and tender feeder roots are close to the surface. In general the root system is the most cold-tender part and will suffer most damage in a radiation freeze. Mulch is an effective counter measure and makes the soil retain some warmth for a short period. After all, mulch will improve the looks of your landscape and add to the overall health of your plants.

Larcher and Winter (Principes 25:143-152) conclude that the distribution of palms around the world is strictly limited by the inability of their roots to survive being frozen. Even the very coldhardy ones, can be expected only in areas where the soil does not freeze.
Experiments found the roots and especially the root tips very sensitive to freezing temperatures. Roots can be damaged already by one or two degrees Celsius below freezing. In particular: Trachycarpus fortunei showed damage at -6.5°C, Phoenix canariensis and Washingtonia filifera were already damaged at -1°C. Having palms planted with portions of their roots exposed, makes it like for the roots to be frozen and especially with young palms could result in death.

CHEMICALS: Recent developments of chemicals and fertilizers have achieved great success in protecting tender plants from freezes. Read more here..

SUMMARY TABLE
To evaluate what design works best for you, find out the specific requirements for a species and know the temperature history of the location. Depending on the amount of time you have to build and the foliage you want to save, various designs may apply. Certainly more than one protection device can be installed at the same time i.e. for a Phoenix you might need warmth, protection from freezing winds and a dry spear. So, you could install a 'Tripod' and a 'Permanent Artificially-Heated Stem Wrapping' at the same time. In order to make your choice easier, see the following table: