I've built a garden wall out of 2 courses of hollow 9" blocks with drain holes, on a foundation course of 4" 7n blocks on their side. Rightly or wrongly!
The wall zig zags at right angles with the longest straight run being 2m. It retains soil but only about 2m at widest point as neighbour has some sort of low wall (slabs on their side).
Do I need to fill the hollow blocks with concrete and reinforce with rebar? Given the neighbours wall hasn't fallen over in all these years, I'm wondering if I'm going ott. Would like to put timber on top, so I guess I'd need to fill with something.