As we withdraw into our houses during the colder months, our evergreens have to stand outside in the frost without any protection. If the cold is too severe the leaves and shoots can discolour and die quickly. For that reason, cut away all dead twigs and foliage so that the plants can produce shoots in their place.
When it freezes, water is bound in the earth and cannot be taken up any longer by plants. Evergreen plants give off water in winter as well and therefore dry out easily because the roots cannot obtain any more. Sunny days in winter and wind intensify this effect. As soon as the worst of the frost is over, cut off the dead tips - you can recognise them by the spongy tissue and brown leaves. Be sure to water your evergreens on frost-free days to ensure they absorb the maximum amount.
The parts of plants that are above the earth are especially likely to be frozen when there is frost. You can detect slight damage due to the leaves turning partly yellowish or reddish. If it had frozen more strongly the leaves become glassy or brown. Frozen shoots turn dark brown or black. Buds and flowers usually drop off the plant. It is best to remove the dead parts completely, and most perennial plants will recover quickly.
If the sun is somewhat warmer again in the day but the nights are still cold and frosty, this is the greatest danger for trees, especially for the south- and southwest-facing side. The constant change of temperature is hard on the bark and also the wood. The wood expands due to the warming and the sap in the cells becomes more fluid. This produces severe tensions when it freezes, causing frost cracks and gaps. To some extent the bark also comes away in sheets. This applies to trees as well: cut off the dead parts and apply tree wax to treat the wound. If the damage is greater a tree bandage may even be necessary. Prevention helps here as well: apply a white coat of lime paint to the trunk before the winter. This will reflect the rays of the sun and the trunk warms up less.
Just score the bark lightly with your fingernail. If you see fresh green tissue underneath, then the twig is OK. On the other hand, if it has turned a yellowish green and is drier, it has died and must be cut off.