Hi Humbug, I haven't tried sharp sand but would think it would help. I have found making a kind of raised bed, no sides or anything, just soil heaped up and levelled off helps. Ground is fairly heavy here and with lots of rain, they need a bit of help or end up a sodden mess. In the past I’ve grown Autumn Champion, Radar, Senshyu Yellow, and a red one Electric, which tends to bolt a bit more than the others. I've gone for Radar and Senshyu Yellow this year. Pretty sure I've grown Troy before too, just can't remember how they did. It's lovely to have onions ready to harvest early, but I find come spring some will bolt. I just use those ones first.