rock mulch

I'm a newbie, and have only looked at this site when I've had specific problems, as we're still busy landscaping our new house. Now I'm up to the stage where I have to pay a bit more attention to the soil, having installed adequate drainage behind the retaining walls. Once that's completed, I intend to create rock gardens, and intend to use rock mulch on the garden beds, instead of the more traditional types of mulch. We live in the southern part of Australia, where we've just come from a drought, but still have water restrictions, and summer is just around the corner. One of my aims is to be as conservative as possible with water, given that we've already established a tropical garden.
With the laying down of rock mulch, I believe I'm supposed to lay weed mat first, on top of the soil, and then lay the rocks on top of this. Is this the best way to attain my ambition of retaining moisture below the soil? And, other than the weeds that will inevitably grow in between the rocks in time, is this a good way to reduce the amount of weeds? I'll be installing drip-feed irrigation hoses just below the surface, to assist in providing enough water to the plants. Also, there will be a "dry" rock garden creek, in which I'll introduce a level of fall to direct additional rainwater to these plants. (I'll lay butyl below the surface of the "dry creek" bed to assist the water runoff to the plants along the way).
Also, does anyone have any ideas on the proximity of rocks to plants? I hope to grow moss on some rocks, but there are a lot of palms and birds of paradise, tree ferns, birds nest ferns and other tropical plants that might not appreciate the proximity of sun-heated rocks near their trunks.
Thanking you in advance for your replies!
Casey.
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oops, I must have posted an off post topic?

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It all depends upon how you wish to treat the soil, or how you wish to grow your plants. For example, the Gotelli Conifer Collection at the National Arboretum is mulched in granite gravel without a weed barrier. The drainage is decent, and as the granite slowly decomposes its adding acidity to the soil. It supresses weeds somewhat, and those that do spring up are easily pulled. How weedy is the soil to begin with?
Perhaps a good compromise would be to lay down a generous layer of newspaper or cardboard first, then the gravel on top. The paper barrier will block weeds for several years if not heavily worked, and as it decomposes it enriches the soil somewhat. Other biodegradable weed barriers include Curlex and jutte blankets...
Dave

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Thanks David, Yeah, I'd read about granite increasing acidity, as well as marble and limestone too. I've already got a lot of "river rock", a black rock rounded by the actions of the waves, coming from the coast! as well as slate and sandstone (these two will be going onto a concrete based path and wall) One reason I want to use river rock as mulch is that I can intersperse larger rocks around, which might help hold the smaller ones in place. The problem isn't so much that they'll fall out of the raised/terraced garden beds, as the soil level is about 3 to 4 inches below the top of the retaining walls, but that I've got a very exuberant Staffordshire Bull Terrier, who loves to run around everywhere. I have to let her run around these gardens, as I've already fenced off the herb garden from her. Thus the rounded rocks, which won't be so hard on her paws.
Thanks for your tips on newspaper, I've been saving some for some time, so should have enough soon. And it'll sure save money! I cleared the weeds a fortnight ago, but I notice that the front garden (cleared the week before) is already resprouting weeds. So, for now, it's relatively weed free, and I intend to keep it that way for a while. I'm yet to lay down some more drainage and electricity and water cables for a future rock water garden, as well as below surface drip feed irrigation lines, which will give me an opportunity to add more compost to the heavy clay.
Once again, thanks for your comments, I think I'll go newspaper instead of weed mat! I've looked up Curlex, and in Australia, it's a hair product, and jute is only available for insulation, and rather expensive. Hmm, maybe one day we'll learn.
Regards, Casey

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1. Granite rock will increase acidity, but limestone will not.
2. Beware of river rock or gravel, you have to be certain of the source. If it came from brackish waters or near the open ocean, chances are that it contains an intolerable amount of sodium that would kill your plants failry quickly.
3. You'll get waves of weed infestations after the initial clean up, both because opportunistic, fast growing weeds spring up in the now oepn soil, and because you've triggered germination in weed seeds that have lain dormant below the soil. As you ride herd on them their numbers will diminish over time.
Reads as if you have a good handle on the project, let us know how it turns out, including pictures!
Dave

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limestone and marble will bring the pH up. why powdered limestone is used.

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"end rolls" of newspaper, unprinted. The rolls are too small to leave on the big presses and are given away by some newspapers. They are great for packing material for dishes when moving as the dishes don't have newsprint on em and don't have to be washed. It would be easy to unroll in the garden. Nanzi
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Thanks Olde Hippee,
I've just spent a whole heap of money on mulch for our herb garden, the soil was drying out too fast, but I'll use the rest on another patch. Now, your idea about the printers is excellent, because that'll save a heap of money. As it is, I've been convinced by a friend who's got an immaculate garden, to use newspaper as mulch. His plants and garden set up would make Burke's Backyard green (oh, is that a pun?) with envy. He sure has got a green thumb.
All I have to do is wait for the temperature to drop a bit, as it's currently over 35C (or 100F) outside, and that's just the right temperature to survey things with a beer in hand, especially on a Sunday afternoon. Thanks for the advice! Casey

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