Soil ammendment tends to be temporary, & repeat ammendments can eventually
corrupt the soil. Some plants, like camelias, die in soils that have been
ammended two or three times. If one lives in a region where soils are
naturally to the alkaline edge, but wanting a big collection of
rhododendrons, & so truck in acidic topsoil for the collection, a few
years later the soil will have alkalinized to match the larger
environment. I love our naturally acidic soils, but if I found myself
living somewhere to the alkaline side, there'd be a few things I'd have to
give up, but many new things I could grow instead.

Ideally one understands what the natural soils are like in the region, &
if one's immediately accessible gardening areas have soil in need of
restoration or improvement (for instance, because it is all clay, or some
other repairable limitation), it would be ammended toward the natural
state of local soils. That way it might never need further ammendments
ever. Regional soil types are defined by types & percentages of mineral
deposits & topography (such as a valley below lime-rich hills), types of
plants that recycle themselves into soils, & the rainfall patterns & water
tables or amounts of surface water. One selects plants appropriate to the
natural pH levels, finding plants that do best in the actual local
environment.

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
See the Garden of Paghat the Ratgirl: http://www.paghat.com/