One would do for a 90x90cm , but I bought 2, at that price its a no-brainer. As JTang says its not an exact science,with lots of variables, but I dont think there is a better investment at the moment than an MS-006. Since my Auto-pounders went under my second MS-006 yesterday they have suddenly started bursting into flower and are shooting up as we speak. One of my cheeses , close to harvest, now has to be supported as its top cola became too heavy for it to stand unaided.
the best person to speak to is Dan from GN he will tell you all you need to know, just phone them , they want to help- its a great product, with a 3 year warranty, great customer service and help whenever you need it from an expert -- For £249 its a complete and utter bargain