if its wood i wood get a big stapler after painting plenty of preservetive on it first and polythene the inside so the soil isnt in contact with the wood at all if you want it to last a while . youd be surprised how much soil you mite need but hard to say without dimensions and or a photo . lots of people give top soil away if you can pick it up or you can buy it bye the ton from local builders . realy need the dimensions thow sorry .

Depends how much you want to spend really, and how large it really is. John Innes No. 2 is brilliant, loam based, but comes in smallish bags and works out expensive. Otherwise there's multi purpose compost (recommend Wickes own in the GREEN bags, not blue) - I'd be inclined to mix the two together in the container. Depending on what you'll be growing, you could also add something like chicken manure pellets, but add these a few days before you want to plant to give them time to get good and wet and slack off a bit. I wouldn't recommend buying in topsoil and using that, although that's probably the cheapest - it's usually motorway spoil and may well be full of weed seeds, and hasn't been sterilised.

be ok with membrane thow and that isnt the case here but we have a lot of quarries and landfill here so theres plenty always around .

To save on the cost of compost etc when you are filling it up I would also add some broken polystyrene pieces on top of the usual crocks etc and then add the compost.

To save on the cost of compost etc when you are filling it up I would also add some broken polystyrene pieces on top of the usual crocks etc and then add the compost.