Shrubs that are not totally hardy are more likely to be killed by a combination of low temperatures and cold winds than by very low temperatures on their own. This effect is known as wind-chill and it can be particularly devastating for evergreens. Winter protection, in the form of a windbreak, is an excellent idea.
All types of winter protection should have been put in place in late autumn or early winter, but if you have not done this, and you do have vulnerable shrubs, it is still worth taking the trouble to wrap them up if severe weather is forecast. Hessian, perhaps with straw packed inside, will be enough to protect most shrubs. Alternatively, you can make a frame from canes and create a ‘tent’ using several layers of environmental netting or horticultural fleece or bubble plastic. Make sure air can circulate, and ensure that light can penetrate if the plant is an evergreen.
While thinking about protection, do not overlook those plants that are tough enough to flower this early in the year but whose bloom are sometimes damaged by a very heavy frost. The Christmas rose (Helleborus niger) and Algerian iris (Iris unguicularis) are likely to be in bloom in many parts of the country. The flowers on both these plants are delightful, and look lovely in flower arrangements. If you want unblemished blooms to bring indoors, put a cloche over them, or protect them with a supported pane of glass.