Hello everyone. I live in central Idaho. I am new to this discussion forum, recently retired, and like Tolkien's Hobbits, I have a love for growing things but by hook and crook. I just bought myself a little green house so that I can harvest seeds from this years flowers and attempt making my own starts next spring. My question today is centered around amending soil. I have a mountain home on an east facing hillside. Sunrises are spectacular!! I have a retaining wall, approximately 200', that is cut back into the hillside. I have approximately 3' of flat growing area behind the wall before it slopes uphill. The soil is made up of a lot of decomposed granite. This soil is very hard, almost cement hard when it is dry and loosens up like a bowl of oatmeal when is wet. I should have backfilled with top soil but used soil from the hillside. Too late to change now. I have Dwarf Alberta Spruce planted every 8' and used garden to fill the holes and have them on a drop system. So far after two winters the trees are doing just fine. I want to amend the soil between the trees so I may plant flowers and ornamental grasses. What would be the best additions to the soil to make it more loamy and drain well. I do have the ability to use a rototiller. Thanks in advance for any ideas.