even when reading the guidelines, they insert the cover your butt "may", not "will" or "does"... life in a world ruled by lawyers. once it's gone through an earthworm or two, I'm not longer overly concerned.

as for "rule of thumb", the geek once spent a frustrating summer trying to corrolate the "testimonials" in my mom's old Organic Gardening magazines into something coherent .... aaaaccckkkk!!!!

no basic info on growing zone or climate or soils and one article would directly contradict another in a later issue. And don't get me started on the term "organic"... LOL   

general guidelines tempered with facts and reason suit me fine... and I'll still experiment.