Dear Brenjon, i take it you mean my Sweetpeas and not Lizzies.
I sow them about the middle of March in my greenhouse, as soon as they are showing through i just put them in a cold frame, nip the tops out once they get growing, and i find they start flowering round about now.
I must say i wouldn't try and force them on, you will be far better letting nature take it's course and you be rewarded with some lovely bunches of Sweetpeas.
Don't fotget once they start flowering, the more you pick the more they will flower, and don't foget to dead head too.
Kind Regards, Old Herbaceous.
There's no fool like an old fool.