I use around 50-60% sand added to old garden soil (primarily used to be pure garden soil from like home depot, I had tomatoes and veggies that used up all the nutrients from the preiovs year). Soil over time compacts and gets less aerated so i hope that adding more sand, gravel, and mulch bits will help.
My semp/sedum bed (and old semp bed) consisted of around a foot to six inches of sandy mix and there was a thin layer of bark/leaves, and than below that was pretty much just regular garden soil with 10-20% sand. This way the semps get water when I am away from the garden during droughts, whereas they dont get total wet feet. I do end up changing the mix to 100% sandy mix after the plants get fully established. Most don't care though.
If anyone has ever had containers before for a long time such as a year or two without soil maitenence you may see that the soil level "drops", because the soil compacts. Adding chunky things like bark bits, gravel, and sand help it stay fluffy.
You should be able to recycle old dirt by adding fluffy helper ingredients, if your budget can only afford sand/gravel. You'd probably want to add a bit o' fertilizer too.
