Higgs Boson wrote:

What I ask is whether I have to scratch in or bury the coffee
grounds (and banana peels) or if it's enuff just to strew at the
outside root zone & water in.

As with all organic matter coffee grounds need to be composted prior
to adding to the soil. Most books on composting explain not to
compost banana skins, like corn cobs/husks they won't compost for many
years, and then they add very little. Placing uncomposted garbage on
or in your garden soil will only attract vermin and harbor all manner
of plant diseases. If you are looking for a compost shortcut/work
around other than obtaining already composted material there is none.