I too have used oak leaves for decades. I have used these leaves over canna and ginger rhizomes around all types of landscape evergreens and over asparagus (dormant now) and garlic. It goes over my garlic ONLY if the temperatures get down to the mid-teens or lower. I put 4-6" of oak leaves over/around these plants/rhizomes. However I don't shred them with my mower if I am using them only as a winter-protector mulch. I do shred them with my mower when I put them in the compost pile though.