With only a couple of cold spells here on the nursery so far this winter we have just got around to putting our deciduous Agapanthus (planted out in the border) to bed for the winter.
There are 2 types of Agapanthus, deciduous (lose their leaves and die down for the winter) and evergreen (keep their foliage all year round).
The evergreen types require more winter protection than the deciduous varieties. Ideally they want to be moved inside a green house/conservatory or summer house to keep the worst of the cold off them, or at least moved to a more sheltered area of the garden if they are in pots. Maybe against the house.
If they are planted in the ground, and so can not be moved to help them through the winter, you can create a wind break around them to create a little micro climate. This should protect them from the worst of the elements, you can also add straw to the top of them when the temperatures really drop. However, you have to remember to remove this once the warmer weather comes or else it may rot the foliage.
Watch our Youtube video to see how this is done: http://www.youtube.com/watch?v=cPgfayLfBy4
Deciduous types are much more easy going. Cut them back removing all the foliage, and then a mulch with straw will help to protect the crowns. To keep the straw in place we have used a weed suppressant material ( this is a permeable & breathable membrane, it cuts out the light but this is not a problem as the straw is already doing that) to prevent the straw from blowing away and in our case here on the nursery to stop the foxes playing in it. Or you could use green garden netting to keep the straw in place.
This can all be removed in the spring as the weather and the ground begins to warm up again.