How often pings flower and what time of the year depends on the type of ping. Some will flower continuously all year long, some will flower while in a winter bud and some will flower just once or twice a year.
The garden centre wesers will even flower on an east facing windowsill. I have one flowering in an east window at the moment. During the winter months I bring many of my butterworts indoors and they happily flower in a west facing window that is double glazed, so the glass is not the problem.
Give your pings time they will probably flower for you eventually [img]http://www.**********.com/iB_html/non-cgi/emoticons/new/smile_m_32.gif[/img]