Hydrangea Mops Protect Buds From Frost

I usually leave the foliage on old plants to give some sort of structure to the garden during the bleak winter months. Often these look untidy, but they come into their own when the frost arrives, and can on occasion look quite spectacular. However, there is more to it than this. These frozen hydrangea mops are protecting the buds on the lower parts of the stems from frost. They say this is because cover cuts down heat loss to the atmosphere by radiation, though I find this hard to appreciate fully.

I have found that frost seems to be far more damaging if it is allowed to settle on the plant - even glass gives considerable protection in this regard, though will do little to cut down heat loss through radiation (radiated heat passes straight through it, as it does through a tungsten light bulb).

As far as the hydrangeas are concerned, best not to remove the mops until late spring when the stems can be cut back to strong buds.