Can I have views, please, on how to be as successful as possible in
replacing a lawn with a herbaceous garden WITHOUT removing ALL the turf
first! ? :-)

The lawn in question is over a soakaway network and I have been advised
that to remove the turf (either by machine or by slicing it out) might
be to damage the soakaway system underneath.

So, having gathered together a good list of shallow-rooted herbaceous
perennials to "replace" the damnably fast-growing lawn (fed ceaselessly
by all those septic-tank nutrients beneath!) I am wondering how best to
get the plants in.

If I simply dig out holes sufficient to take the average "plugs" of the
average 5-inch diameter potted plants, AND if I monitor those plants and
keep pulling away invading grass for the first year or so, will those
plants eventually get the upper-hand? As they grow, are they likely to
cause the grass to recede, die off? Will they establish themselves?

What do you think?

Eddy.