you could...

soak it (just enough to get it wet, really) for a couple hours until it turns to mush and shred it with a paddle whip using a power drill.

...or you could cut a hole in the top of a garbage can, load it up with the dry, torn bits of cardboard, fit your weed-eater's arm through the hole in the lid and fire that bad boy up. Doing this without a lid is possible but you'll get the occasional piece of cardboard shrapnel flying out at high velocities, lol.

Typically I just soak it and use a paddle-whip to shred it though... :D

I bought a paper shredder on sale and it has worked well the last year. It is a 24 sheet one and eats 10" wide pieces of cardboard and spits out 3/8" wide strips. I use a box cutter to get my 10" wide pieces.

Heavy duty crosscut paper shredder - the kind that can take 50 sheets of paper or individual sheets of corrugated cardboard. You do have to rip the cardboard into strips that will fit, or use a box cutter.

I took someone's suggestion of soaking the cardboad when I made a bed a cpl weeks ago. It worked great - it didn't even "soak" that long - and then it basically fell apart and was easier to tear than paper. I didn't use a paddle whip/power drill - just hands. Cut like butter sitting on a table after a long Thanksgiving dinner :)

All the best,
Tree

I lay card board out in the yard and blow it into the garden with my rideing mower. The push mower works too.

I used to use an 8 hp shreader, but now just put the cardboard into my compost bins and worm bins whole. I find that cardboard rots quite quickly, and so I let the bacteria take care of the work for me. Worms particularly like the boxes, and make quick work of them. The cardboard is often completely obliterated before some of the other readily compostable items. I find this is a great labor saver.
Renais

Thanks for all these great ideas. Sounds like I could also put strips of cardboard into my chipper/shredder ... is that right?

Leslie

Depends on the shredder. Mine isn't so heavy duty and doesn't like cardboard. I found that out the hard way.

Karen

I got a paper shredder that eats cardboard so long as it isn't too thick. My old paper shredder did eat cardboard for a little while but then I think we fed it too much and it broke.

The fellows power shred seems to do pretty well with cardboard. I got one that doesn't take that many sheets of paper at once but it is rated to run alot and still seems to take most corrigated cardboard.

This is all if you really need shredded cardboard. I like to use large sheets of cardboard as the bottom layer for new lasagna beds. I only shred cardboard for use as cover materials in compost buckets or for new bedding in the worm bin. The worms don't really need it shredded as they are quite happy with layers of big cardboard over top of their bedding. A bit of moisture and the cardboard tends to fall apart. I've also found that simply dipping cardboard into a bin or bucket of water will make pealing off tape quite easy and leaving the box in the water for more than a moment will allow it to fall apart really easily.

when I use cardboard I just use it as another layer in my mulch. I use regular mulch under and over it. Great at stopping bermuda grass. I try to avoid the huge amount of work it takes to shred, compost and move material. The only exception I have to this is I use a chipper to chip up my fruit tree pruning. I have a lot of trees and the piles of prunings are just to much otherwise. Even with that, I leave the chipped material right where it lays, I don't move it.