No, no to the Quickrete! [Just add water and get rocks.] Use pure sand, rough builder type, from the lumber/builder area. Or just start adding compost gradually. Or rake in lawn clippings and coffee grounds. In fall chop up the leaves that fall and add them, with a little ground limestone because most are acidic. It all works including my very unconventional burying of kitchen veg/fruit waste in 4-6" wide trenches between irises that are about 24-30" apart [look up "sheet composting"]. In 2 months will not recognize much of anything if redug then. Just don't wrap the clump with the stuff.
