Posted: 14/04/2015 at 18:40
I have only just set my begonia tubers, they are sprouting today. I would say you started them to early and it was just too cold. Give them time, now its warming up a bit they may shoot.
I take it you only just layed them in a seed tray, with compost around the sides, not on the top? Dont let water get on the top of the tubers.
Lobelia and petunias are slow, I always start seeds off in the kitchen then move out to the greenhouse when they grow on.
I have never had heat in the greenhouse, if you dont want to overwinter tropical plants there is no need, and now, definitely no need for heat.