sweet pea seedlings

If I plant seeds straight into the ground they seem to look after themselves and grow well, but whenever I try to grow sweet peas inside, they start off well, then grow too tall , weaken and fall over. I know you are supposed to pinch out te growing tip but when is the time to do that? If I do it too early , won't it kill the seedling anyway?

It's good to have the heat of indoors to get the seeds to germinate but as soon as they have you want to put them into a frost free greenhouse or somewhere similarly cool and light this will then slow the growth right down so they don't become leggy. Yes you are right to pinch out the growing tips once 2 sets of leaves are showing, this will then encourage branching. Link below is to article I've done on my blog about sweet pea seeds.
<span id="sample-permalink">www.alisonpike.com/blog/?p=231

Thank you Alison. That makes sense.

Does the advice about pnching out the growing tip apply just to sweet peas or to any other seedlings?

I always soak mine for a couple of days,sow them in the Green House and move them outside when seeding start to appear I don,t know it this is right?