Mix for very large container?
I have two large [ugly, standard] bathtubs with plenty of drainage holes* and I want to repurpose them to large raised beds for annuals - both winter and summer. I haven't decided if I want shade or sun - but if I put them in a spot between a crepe myrtle & mimosa, I can have winter sun & summer shade.
What's the best type of mix to put in a container that large? Gritty would be too cost prohibitive, but the 5-1-1 would probably be not much more than buying a "premade" soil. But is the 5-1-1 good for something that size?
Picture of basically what I want to do: http://blog.littleinsights.com/2009/04/30/reclaimed-wood-planter-box.aspx
Story on unfortunate bathtubs can be seen here: