I've successfully used both, together and separately. Whatever you can get your hands on for free and easily is the best option!
On a different note, you mention using "small landscape rocks" as part of your mulch. I highly recommend keeping away from stones as mulch in nearly all situations.
Unless you constantly weed/poison, it will very quickly look bad as weeds grow through it. And don't even get me started on landscape fabric...

So rocks on top of cardboard and a little soil would not work to keep out the weeds? Wouldn't it be the same as using mulch?

Well... I think feijoas is simply saying that if you use rocks as a mulch, grass and weeds will grow between them and it is a total pain in the neck to weed them. I put down cardboard and then compost and have had zero problems with the grass beneath the cardboard.

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Rocks don't form a barrier like bark: they tend to roll arround, exposing soil. They also tend to 'migrate' into annoying places IME. I find anything that isn't designed to break down a pain, but I know it's a bit counterintuitive.
And of course I should've emphasised that my rock-and landscape-fabric aversion is very much not shared by all!Jon, how long've your rocks been down? I'm curious as the cleanups I've done on this kind of thing are usually a few years after the rocks have been laid and the inevitable OM's providing a good bed for wind/bird carried seed.
My big worry isn't the grass under the cardboard, it's the weeds on top!

Hi feijoas,
I couldn't agree with you more...
My whole garden is on a gravel parking lot/driveway....
So I just do the best I can with the cards I have been dealt.
It isn't the best,but with a little extra work...it's do-able ;-)

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It is not a matter of either or but a question of what you have readily available. Both cardboard and newspaper do the same thing, cut off access to sunlight for any plant covered by either one which will then cause that plant to die. Cover the cardboard or newspaper with some other mulch material both hides that paper and holds it in place. The best material to use is vegetative since that will help provide some organic matter to the soil. Stones may well do a better job of holding the paper in place but they will not contribute any organic matter to the soil although stones will allow OM (dust from the air) to accumulate in the spaces between the stones which will allow unwanted plants to grow.

My experience is; weeds will grow anywhere.

I've had rock mulch in the past. The problem I had was that when it came to pulling the weeds out of the rock, I had to root around trying to move the rock around if I wanted to get the root.

With a more organic mulch, I can usually just pluck it out because it's trying to grow on top or I can move a little dirt to get the root.

I also find that the more organic mulches keep the ground more moist than the rock mulches which makes it easier to pull the weeds.

Just my experience though.

Val

Ah, a parking lot. That makes sense then. I had kind of wondered "why all the rocks?"

Both cardboard and newspaper will work great. I generally prefer cardboard because it is easier to collect and lay down, big pieces cover a much larger area. The only drawback of using paper is that pieces sometimes break off and litter around, and it looks a little unsightly. But anything paper breaks down and disappears eventually.

Isn't rock mulch commonly used in desert areas? My sister lives in Sedona Arizona and it seems they use that red rock mulch in lieu of grass.

Cardboard and newspaper work equally well IME. I've used pine branches and/or shredded leaf mulch to cover them. Having had bad experiences with marble chips I inherited from a previous garden owner, I will never inflict those on anyone who might follow me. That said, I'm in New Jersey, where weed growth is rampant. Gardeners in desert areas that have less of a weed problem may find it easier to use rock/stone/gravel mulches.

Thanks for all the answers and amazing pictures, guys.

I strained my back at work a couple of days ago so am slowing down considerably on this. But I am collecting cardboard everywhere I see it and will be using that. I agree that cardboard is much easier to lay down. I have used cardboard at the bottom of two raised beds - so far so good! But those were on already baked, bare patches of solid clay, so I don't expect weeds to suddenly come forth.

I think I'll be passing on the rocks for now, based on your responses.

I find it much easier to accumulate newspaper than cardboard. Its remarkable how fast newspaper accumulates if one is delivered daily while to get cardboard I have to drive to find someplace that has some if they are not recycing them and will allow people to haul some away.