Well, what i do, and also some friends on in their garden, is first digging a hole from quite some liters, like a very big pot, in there we trow a big sac or even 2 of good soil, i personally think its better as the ground we never know whats in (unless you are able to analyze your soil) which can cause several issues as maybe the soil is too acid with too much nitrogen or whatever right, so its up to you but i think thats the best solution