Thanks for the reply Geoff, guess it makes sense that as the sand/ballast is inert then it should be OK to reuse - we'll soon find out....!

Last year I grew some of my tomatoes using Terry Marshall's ring culture method (KG April '03). This worked very well and I intend to use that method again this year. But can I use the same ballast/sand mix or should I use a new mix, or could I use a natural product like Growing Success Greenhouse C...