I love mesembryanthemum and for two years I've tried to grow my own. They germinate readily enough, in a tray of coir on the kitchen windowsill. But they're so fiddly to transplant, I'm sure I must be damaging the roots. I transplant them into yogurt pots of coir, put them in the cold frame, keep them fed and watered, but they don't grow, they merely survive! Any tips?