Colleen wrote about irises and piling leaves on them. It's not clear what kinds of iris you grow, probably tall bearded? Most iris should be cut back in fall or early winter. Then, winter mulch in dry cold climates should not be a problem, unless it gives rodents a foraging advantage. [In wet winter areas, dense mulches like hardwood leaves can create serious fungal problems for irises.] Don't forget to pull the mulch back in spring. Do think about creating a compost area for those leaves and other suitable garden debris. Kathleen Kathleen Sayce PNW Coast, WHZ 8, dryish cool summers & mild wet winters