Never use tyres if they are out in the sun as the leaching process is increased. I know, but cannot rememeber the compounds sorry. If it is under ground the leaching is greatly reduced, to the extent it is safe (not for food areas). I use mine for retaining walls and cover with chicken wire and then render with cement with associcated drainage and tie downs etc.
I find it better to buy the spuds (certified) for growing less fungal issues and a better crop.
Number one rule (I am sure most of you know this) rotation and try for at least tow years before putting the same type in the same area (3 years is better but very hard in a small area).
I have 3 beds 10 metres long and about 1 metre wide with a least one metre between each row (rows run magnetic North).
I have no grass clipping as I do not use a catcher. A good use for them is newspaper on weed areas and then the grass clipping. It can also be used to start a new area and clean up the weeds.
