If you mean the compost from your finished pots/baskets? I always just put mine on the garden and put new in the pots as I plant up.I also do this with growbags. If you keep the compost in the containers at least remove the top third and replace and add a good long lasting fertilizer. Inspect for pest and disease too.

If you are a cheapskate like me, you can put it out over a plastic sheet around a foot deep so it can be weathered during the winter. By spring, though it may have a few weeds in it, it is wet and peaty and you can then mix it with 25% compost from the compost bin for potting larger plants, or mix in some organic or inorganic fertiliser. The weathering process will wash out most diseases and nasty bugs, but I wouldn't use it for seeds.

Bertifox, that's the second time you've called yourself a cheapskate - you're not, you're being helpful to the environment by recycling AND frugal at the same time. Gets my vote every time, don't consider it cheapskate, just common sense...