In case someone has the same problem, you must convert the date using datum()
here is the code I used:
date = datenum(date, 'yyyy-mm-dd'), 'mmddyyyy'; plot(date, p_open) set(gca,'XTickLabel',date) datetick('x','mm-dd-yyyy','keepticks')
Thanks Jan for the suggestion. I'm not sure why but the labels are broken into about 2 month periods (there are 3 points where it is a 1 month period)