I only mulch, or mound up with earth, my corn plants if they start to grow roots from the bottom of the stems (adventitious roots) it gives them more support if it is windy.
The only other thing that gets mulched, here, would be potatoes when they can't get earthed up any more and potatoes start to show on the surface. Then I tend to use grass cuttings from the allotment paths.
Can't think of anything else atm.