If you shred them they'll break down faster, but if you don't shred them, they'll still break down.

There is a large difference in the break down of dry corn husks vs green ones. As bpgreen stated they will still break down but the dry ones may take a couple of seasons to do so depending on weather conditions and what your other layers are. Green ones will be gone fairly quickly.

These are green. Straight from the huge waste barrel at the supermarket. So great, I'm just going to toss them on!

I'll be layering them with coffee grounds, composted manure, grass clippings and in the fall, leaves.

You might want to layer in some shredded paper until you start getting leaves. Those other ingredients are all higher in nitrogen (greens), so you could get a stinky mess .

You don't have to shred anything. But the smaller something is the faster it will decompose. Whole trees that fall down in the forest still decay over time - it just takes longer.

You just have to balance out how much time and energy you want to put into the project, how soon you wnat to be able to have the plot ready for planting, and what you want to plant in the space. If you are going to plant fruit trees, seedlings, or sow seeds right in the plot will all have an impact of what the soil texture needs to be in order to be successful.