how best to reuse compost
I have an all concrete garden so everything i've grown has been in pots and a reusable large grow-bag (almost 100 litres).
Having harvested my garlic and onions i have alot of used compost that ideally id rather not waste if possible.
I know i shouldn't plant onions or garlic in the same soil again.
Can i do anything to it so that it can be reused and if so what would be best to plant in it?