How long, or how many times can compost be used in tubs or baskets?? Or is it more a case of keep giving it food as in say a top dressing of bonemeal etc! i.e. I have bulbs underplanted in barrels and would be loathe to remove them, not to mention the cost of renewing the compost!! Any guidance welcome??
If you have permanent planting in a pot, I would remove as much from the top surface as you can and replace that with fresh compost. You could then boost the nutrients and add some sort of fertiliser- maybe slow release fertiliser. For non permanent planters, I would replace the compost annually, but use the old compost in the borders.