How to prepare your plants for cold weather:
First, let’s make sure the soil around the plants is moist, I said moist not sopping wet:
Watering landscape plants before a freeze will help protect them. A moist soil will absorb more solar energy than a dry soil and will reradiate heat during the night. A moist soil can raise minimum night temperatures in the canopy of plants by as much as 2°F. However, prolonged waterlogged soil conditions will damage the root systems of most plants.
Second, cover your plants with sheets or plastic:
Covering of tender plants left outdoors during the winter is not always effective or practical. However, it can help, but only if done right. Improper cold protection via covering can be worse than not covering the plants at all.
Temperatures are usually only a few degrees warmer under the covering, this is often enough to get a sensitive plant through a cold night. Coverings protect more from frost than from extreme cold. Covers that extend to the ground and are not in contact with plant foliage can lessen cold injury by reducing radiant heat loss from the plant and the ground. Foliage in contact with the cover is often injured because of heat transfer from the foliage to the colder cover. Some examples of coverings are: cloth sheets, quilts or black plastic. It is necessary to remove plastic covers during a sunny day or provide ventilation of trapped solar radiation. A light bulb under a cover is a simple method of providing heat to plants in the landscape (plugged in and turned on of course).
Covering with wheat or pine straw:
Wheat straw or pine straw can be scattered loosely over plants low to the ground and probably left during a cloudy cold day, but removed if the next day warms up. Wheat or pine straw can be removed with a leaf blower; however it will create a big mess to clean up.
Covering with water – use with caution:
Plants can be protected during a freeze by sprinkling the plants with water. Sprinkling for cold protection helps keep leaf surface temperatures near 32°F (0°C) because sprinkling utilizes the latent heat released when water changes from a liquid to a solid. Sprinkling must begin as freezing temperatures are reached (around 33°F) and continue until thawing is completed, again around 33°F. Water must be evenly applied in ample amounts to maintain a film of liquid water on the foliage. Keep in mind this my mean leaving the water on all night. No need to do it 1st night and not be able to on the 2nd night. It also means someone staying up to determine when to turn the water on and off. An accurate thermometer should be placed near the plant that is to be protected, not on the house 6' above the ground. Irrigation for several days will more than likely result into water soak soil consequently damaging the root systems and plant breakage due to ice buildup on the leaves and stems.
What to do after the freeze: Water Needs
Plant water needs should be checked after a freeze. The foliage could be transpiring (losing water vapor) on a sunny day after a freeze while water in the soil remains frozen. Apply water to thaw the soil and provide available water for the plant.
Severe pruning should be delayed until new growth appears to ensure that live wood is not removed. Dead, unsightly leaves may be removed as soon as they turn brown after a freeze if you desire. New growth and young branch tips may be damaged while older wood is free of injury. Cold injured wood can be identified by examining the tissue layer just under the bark for black and/or brown discoloration. Prune these branches just past the point of discoloration.