i mulch with licorice root - it looks really nice, holds it's color well and doesn't wash away or blow away if it's dried out and it's easy enough to move aside when something needs moving/planting and can be moved back to cover any bare areas. it also breaks down pretty nicely so it adds to the condition of the soil.
i put down a good layer of leaves in the fall - i crumble them up a bit and pack them down a bit, too. i remove them in the spring
- leaving the bottom-most layer because it's started to decompose.
i turn over the top layers of leaves and mulch and work it into the soil and then apply a new layer of the lic root. i put a thicker layer around plants
like the hydrangea - which are very sensitive to lack of water and the mulch really helps to hold the moisture in. i put a thinner layer down over the areas where the bulbs are...don't want the shoots to have too rough a time growing
up and reaching the sun.
if you've got a lot of newly planted items and/or things that might be iffy for your zone
, i'd strongly recommend putting down a good layer of something to protect them from a potentially bad freeze during the winter (and it DOES get cold up there in ND). once the plants
are well-established you don't, necessarily, have to be so diligent about it.
for overwintering, i've just always done the leaves thing - they're right there, so why not? and i do tend to go a bit overboard with it...which helped the one year when we got a lot of snow (30+ inches in one storm after 12 or so the week before).
the reasons i use leaves: 1) they're FREE and 2) they're nature's preferred method 3) they break down and provide nutrients 4) they're FREE ( oops!
ditto what daylily said about covering the plants
...you only need to do that at night. unless you've got something like a hibiscus and some varieties of bamboo - they would need to be properly wrapped to make it through the winter (with burlap).