i have an ericaceous raised bed too. just finished it. it's got a forest flame and a couple of dwarf rhodedendrons. it's about 8' x 4'. it's two inches of ericaceous compost and the same compost around the root balls of those plants. i add teabags to one corner that's mostly topsoil. i hear you can use coffee grounds too. or a cup of white vinegar per wateringcan when wetting compost