I'm planning to grow some annual wildflowers (Flanders poppies, cornflowers, etc) in a long hessian planter (70x30x35cm). I've currently got a coir-based mix with some all-purpose compost mixed in. I've heard wildflowers don't need particularly fertile soil - but is there not enough organic material in this mix? Would I need to add things like chicken manure pellets or bonemeal/fish blood & bone? Thanks!