One of my favorite gardening writers is Slate’s Constance Casey, and darned if she
doesn’t weigh in on the topic we’re having such a lively argument about here on the Rant – leaves and what to do with them.
It’s fine to simply leave leaves on perennials. By spring,
they’ll have broken down into humus. The ideal would have been to run a
lawnmower over leaf piles and put the chopped-up leaf litter around the
plants. Lacking a working lawnmower, what I did was collect leaves in
hidden piles to break down on their own over the winter and use in the
spring or the following fall.
One caveat: Don’t use oak leaves. Part of the mighty oak’s mightiness
is that the leaves are slow to break down—they’ll make a layer like
Naugahyde. Other big leaves, like maple and tulip poplar, mat together
and in northern gardens can freeze into a giant pancake that keeps
water and air from the soil below.
I’ll tell ya, here in Maryland, that "Don’t use oak leaves" is pretty much a deal-breaker, given our oak-dominated mix of species.
Check out a couple more of my Casey faves: How not to be intimidated by Roses", and "How to plan an attractive and functional garden," with which I agree 100%.