Evert do you find that these plants seem to die when they get several inches high for no reason. I have one plant that I planted in October which is doing great and will soon bloom. All other attempts have failed and I am not even going to try again because it's a terrible waste of seed that is hard to come by until I can figure out why one plant is thriving and all others have died.
I had a few plants die when the aphids snuck into the greenhouse at work on some hanging baskets that one of the girls wanted to winter over. I found some lady bugs and they got rid of the pesky things.