I sow my sweet peas quite late, in the middle of March, so that I can get them in the ground once the soil has started warming up and the roots can go straight down rather than going round and round in their pots.
I sow them in the greenhouse, three seeds to a 9cm pot, then get them out into the cold frame as soon as they've germinated. By the middle of April they were looking like this:
I planted them out at the end of April:
I pinch the tops out so they send out strong new shoots so by today they were looking like this:
Now all I've got to do is put up some support for them to climb up; it's up to them to get on with growing and make lots of nice flowers for me.