When the temperature level drops below -5 Celsius, some shrubs can be affected such as fuchsia. Below -10 Celsius, many others are damaged, such as cordyline, griselinia and phormium.
Temperature levels dropped to minus 12°Celsius in some places in the first two weeks of 2010 and perhaps a degree or two lower in others, some - 17. This is very cold - these temperatures are plumbed only every fifteen or twenty years, and then only for an exceptional night or two.
But the big freeze saw low temperatures last for a week and more, without thaw, depending on location. When this happens real damage is done to plant tissues. They freeze and the ice crystals slowly grow, just as the ice thickens on a lake, and eventually the ice bursts the cells and the cells die.
Very often this damage appears as dried out leaves, or mushy leaves, but sometimes the damage is done inside the plant, in the buds or in the cambial layer, that slippery layer of cells between bark and wood.
Cordylines and phormiums keel over, the soft centres of these plants killed by freezing. Griselinia and escallonia hedging too. The damage does not become evident for a few weeks, when anticipated growth does not happen. In the meantime, nothing to do but wait and see what happens. It is not unusual for some shrubs to sprout low down on the main stems or even from below soil in some cases.
Do not cut away the top until you can see where the new growth is coming from.
If you lift some bark with a knife at ground level and the wood is brown underneath in a few places, the shrub or tree is dead.