I have recently redone my deck and there was an area where the previous owner had a pool. There is a good amount of sand...too much to get rid of. As a temp fix I was thinking about building two 3'x6' planting beds to cover some of it up. What I was wondering was should I put dirt on top of the sand and plant? Or should I just fill the beds with mulch and sit some pots on top of the mulch? If I fill it with dirt how much is enough for the sand to not have an impact?
I would go with about a foot of good topsoil for most planting or at least six inches and then add some potting soil to fill. I wouldn't spend the money for all potting soil. 3x6 is a good size for a raised bed which is what I presume you are talking about building.
One thing about it, you won't have to worry about drainage with all that sand.
If it's worth doing, it's worth doing right. If you wouldn't put your name on it, it ain't done right!