Rather than build raised beds, I opted to plant them directly into the ground. It's mostly just crushed lava, but I've been applying mulch and a bit of dirt for the past year, gradually building up a little something that could....by your wildest dreams....be called soil. Not much there, but it does full in between the lava now.
The big problem now is water. The stuff I'm calling soil is hydrophobic organic material. Very difficult to get it wet, but once wet, it can be maintained. Pouring a bucket of water onto the stuff is a waste of good water. It just runs off. Doesn't get the "soil" wet. But I discovered that if the water is gradually trickled on, it gets absorbed.
I wish I had a drip irrigation system, but hey, I don't even have a water system. So what to do? I opted to try using old milk jugs with a pinhole in them. That way the water could drizzle out. I figure that there was nothing to lose trying it.