I have Agapanthus, one in a pot which I lost this winter because they became too wet and one in the ground under my kitchen window facing west, which is great has survived as usual, the one that survived is a white one and I ve had it for about 10 years the blue one in the pot normally pulled through winters with out any protection on either but alas not this one, yes make sure its got grit if potted at the bottom for free drainage, I used ordanary garden soil in my pot about 8 years ago.

Both of mine are in pots and I put them in my polyt each winter. I don't water them between nov to mar.

Mine is in a pot - east facing in a sheltered position against a wall. The front half didn't survive but the back has and its got masses of roots all over the surface.

In the ground, hardier ones like the Headbourne hybrids should be fine - all the ones I've planted have come through the winter unscathed. In a pot they're much more vulnerable during bad winters, so probably safer to move them under shelter. Also make sure the variety you buy isn't a tender one - some are and will never make it through a bad winter, and often not through an average one.