As Gardener says, providing it is clean, I use mine for potatoes early in the season (handy as you 'earth them up' as the potting compost becomes available!). Later on, I us it for my toms in pots or for my annuals in tubs because I'm going to feed them all well anyway.
If I have it, I add a layer or two of chopped comfrey leaves into the pots as I fill them.
AC