Question:
We had read an article several years ago in which Israeli carnation growers found that by spraying Potassium nitrate on their crop a day or two before an expected freeze...they received that 3-4 degree protection. Here again this is why most growers in Central Florida use frost blankets (2 1/2 oz. fiberglass material) to protect their crops to include strawberries. Keep in mind that after the ground temperature reaches 60 degrees F (at least in Palms) the plants have a hard time absorbing minor elements. We have heard that even at Fairchild Tropical Garden, they had tried to manually sprinkle the meristem area of the plant with minor granular crystals hopefully to be absorbed to protect the plant from the frost.
We have noticed (primarily watching palms freeze) that plants freeze from the bottom up. We attribute this to the fact that the nutrients in bottom leaves are being re-absorbed by the plant for future growth. Since cold damage is a result of the cell-walls basically exploding due to the water within it freezing...it would make sense that since salt-water has a much lower freezing temperature than fresh-water, that the more fertilizer (salts) applied prior to any freeze would assist in its survival. We have come to the conclusion, that we would rather lose new growth to a freeze, than starving the entire plant of the nutrients it needs to survive.
Bob & Marita

Answer:
There's some truth to this, but it is a much more complicated story..

The statement is correct in that increased nutrition increases the total soluble salts in the cells which lowers the freezing point a few degrees. What this means is that cells that are damaged normally around say 29 degrees, if well fertilized before a freeze, might survive 26 degrees. This has been proven in Bermuda Grass golf greens by spraying them with liquid urea the day before a freeze. It is also one of the (many) reasons I feel that fall fertilization is the most important time to feed palms.

The problem is that this minimal change in cold hardiness is only useful in marginally subtropical or tropical areas where a few degrees difference can be critical. In temperate areas, where the temperatures are in the teens or even lower, it would not mean as much.

About freezing from the bottom up and relating it to the movement of nutrients is a stretch since only potassium and magnesium are mobil and move out of old leaves to new. This might be arguable, but I think it really isn't much of a factor. Normal hard cold damage does damage the mature leaves, but the newest exposed growth is damaged just as much. Of course, the unexposed apical meristem is protected to some degree since it is insulated in the heart of the palms.

Dr. Henry Donselman, Palm Specialist
Website http://www.homestead.com/donselman/

Answer:
To increase the cold hardiness of palm trees, coming into winter, use a granular potassium fertilizer like 0-0-60 or something of that combination that is applied 45 days in advance. It needs to be applied at least 45 days in advance in order to get into the plant's system. What the potassium does is strengthen the cell walls of the plant and will displace the amount of water in the cells making it harder for them to burst during freezing temperatures. Water freezing, expanding and bursting.

Grant Stephenson
Horticultural Consultants, Houston, TX.
Hou,TX Area Chptr IPS V11,I1,Jan.2k.