Down here in NZ, it's not a xeric region and drainage is our biggest problem, thus I keep my best stuff in pots and plant out the toughies in a limited, house-side space that Im slowly raising. I have to say, agaves and aloes seem to love rocks. They love the heat they gather and radiate, they love the minerals that leach out of them and the texture they provide for anchoring roots etc. Luckily I live in an old quarry so if I want rocks, I just bust some off a wall with a shovel or pick and arrange accordingly. Im convinced they help guard against frost damage with their heat sink properties etc. Not to mention, nothing really beats the look of good rocks. They're aesthetically primo. Riverbed cobbles are common and easily obtained down here, but I find them very heavy for their size and they can compact the soil beneath to the detriment of the plants when used as a top dressing, I find.
I also use flat rocks to create zones of run-off and to direct excess water away from some plants, using a layered tiers and this can be surprising effective; I've lifted a rock after a wet winter and found things pretty dry beneath.
Personally, perlite drives me crazy with it's refusal to remain where you put it, especially if you're anticipating significant volumes of water or heavy downpours etc. I adore pumice because it stays put, doesn't suck up water and improves almost any other substrate you care to name. I just use whatever bagged cactus mix is in the shops and cut it with half pumice; this has a pretty good success rate for moi. I don't think most species of agave and aloe are particularly fussy, though I have used peaty mixes in the past and had some rotting issues. I avoid them now.
What I want to know is- who fertilizes their succulents and what do you use??? Looking at some of my specimens, Im convinced they could do with some very dilute manure or potash, as most other plant groups benefit from these two. Does anyone use a commercial fert? Anyone killed anything with it yet ?
