Before you rush out and buy a sundial, remember that each sundial is manufactured for a specific reading from a certain part of earth. All sundials are constructed of a horizontal plate and a little triagular piece which juts out (technically called a gnomon) - this little piece sits on the noon line.
Sundials aren't terribly accurate in telling time - so you can't expect a sundial that is mass produced to read the right time for every part of the continent. Sundials that display real clock time must be custom-made for their specific latitude & longitude and time zone. Not only do the lines on the sundial plate telling the time vary from place to place, the angle of your gnomon will vary accordingly as well.
If like some gardeners you are purchasing one purely for decorative purposes in the garden, then you wouldn't worry about it telling the time, you have your trusty digital clock to do that for you!
Even if you aren't particularly fussed about it telling you the right time, the least you could do is to place it so that the gnomon points as close to true North as possible (use a compass).