fit data with x axis already formatted with dateticks() MATLAB

I have been at this for hours, i feel like the simple problems take the longest which is annoying. I cannot seem to fit a curve to my data, i've tried fit(), polyval(), and I cannot get them to work. I think the problem is, my x axis is in months, not really numbers so the functions hate me right now. Here is my code:

startDate = datenum('01-01-1985');
endDate = datenum('12-31-1985');
month = linspace(startDate,endDate,12);
waterLevel1985 = [75.2 75.3 75.4 75.6 75.7 75.75 75.6 75.5 75.3 75.25 75.2 75.25];

p = polyfit(month,waterLevel1985,4);   %error is here apparently...
x = 1:0.5:12;
bestFit = polyval(p,x);
plot(month,waterLevel1985,x,bestFit)

ax = gca;
ax.XTick = month;
datetick('x','mmm','keepticks')
When i plot, I get a graph with jan feb mar apr....etc as my x axis, and the water level values for1985 on my y axis. If I just put plot (month, waterlevel1985, 'r+') I don't get a fitted curve to my data (which looks closest to a 4th degree polynomial). Please help me do this, I cannot figure it out!

EDIT: I've even tried putting [1:1:12] in the polyfit function instead of month and it still won't work. I've been fooling around with polyfit and polyval but they won't work for me. I've even tried the following:

startDate = datenum('01-01-1985');
endDate = datenum('12-31-1985');
month = linspace(startDate,endDate,12);
waterLevel1985 = [75.2 75.3 75.4 75.6 75.7 75.75 75.6 75.5 75.3 75.25 75.2 75.25];

p = polyfit([1:1:12],waterLevel1985,4);
x = 1:0.5:12;
bestFit = polyval(p,x);
plot(month,waterLevel1985,'r+')
hold on
plot(x, bestFit)
hold off

ax = gca;
ax.XTick = month;
datetick('x','mmm','keepticks')

Answer 1

[Chad Greene]

The way you define months is incorrect. You're actually just picking 12 datenums spaced evenly throughout the year. If you want months, get them by by:

t = linspace(startDate,endDate,12);
[year,month,day] = datevec(t);

[Damian Connors]

what is in the [year month day] datevec(t) vector? I don't understand what that line is doing, could you please explain a little further so i know what to replace in my code?