Mine is pretty inconsistent and has stalled out a bit this year both on the flowers and the growing, but it has had some nice flower displays.
You might try some miracle grow rose and bloom or orchid fertilizer late winter/early spring when it wakes up from winter dormancy.
This one gets morning sun and then shade the rest of the day. I have a whole bunch of mammillarias in hanging baskets all on the east facing side of my house. Have to replace one or two every year as some can be quite finicky when it comes to watering, but the ones that take tend to do quite well and provide pretty good flower displays over the late winter to spring, some going into early summer.
Here is Mammillaria sphaerica that was in bloom till mid-June as M. guelzowiana (2nd pic, the same plant as the one in my earlier posting just with a bunch of growth and more sun so a more compact flower):
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I missed the most recent flowering on my M. grahamii, but here is it in late June:
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Unlike Ron, I have not had a lot of good luck with Mammillarias in the ground. I have a few, but that is where I have lost the most...