I had a digger remove top soil from our backyard so that I could install raised garden beds with pebble paths between them. The soil was removed a few cm deeper than I'd planned, and the level of the pebbles needs to align with concrete paths/pads. If I use just decorative pebbles for the paths, I'll need substantially more of them than originally planned, and they aren't cheap.

There is woven weedmat on the ground ready for the pebbles to be brought in.

I consulted the local landscape supply business, and they suggested using a layer of scoria (a light, bubbly volcanic rock, excellent for drainage) underneath the pebbles. Scoria is substantially cheaper than the decorative pebbles.

Given that scoria is very light (as rocks go), will it rise to the surface and mix with the pebbles as the path is walked on, over time?

  • The best paths are made of crushed rock not decorative pebbles. Scoria or volcanic rock does not make for better drainage in any universe. What are you edging with? Install PT 2x4's for edging. and allow 4" above undisturbed subsoil to accommodate 4" of crushed gravel; 3/8 minus is the best for landscape surfaces and paths. Rounded pebbles, pea gravel, river rock or gravel do not make a good walking surface. I am thinking you mean landscape fabric has been installed beneath the gravel? That is very good. LS fabric is not and will never be 'weed' block fabric. – stormy Sep 14 at 8:04
  • @stormy Thanks for your comment! Yes, it looks like "landscape fabric" is the same thing... it's normally called "weedmat" in New Zealand eg here – Highly Irregular Sep 14 at 8:31

I will assume there is a reason why you can't simply lower the ground level below the pads. I will also assume there is a reason you can't simply add some of the dirt you removed back.

The scoria most definitely will mix with the pebbles over time. Scoria is excellent for drainage and will help maintain a balanced moisture content in the rocks; however, why would that matter lol there is nothing growing in the rocks.

Personally, I wouldn't have suggested you put scoria down. I would have suggested you put dirt down.

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