[juvenal]

Plants are 6" high, and tips pinched out. When can they go outside?

How hardy are they?

Thanks

[mumofstig]

Start hardening them off now, outside all day and in at night for about a week, then outside permanently. They are classed as hardy annuals but not sure they'd like snow or ice 

[sunshineband]

They are very tough once hardened off. Mine stood freezing temperatures well, even in their pots (The ground was too solid to plant them) and at planted in the ground now.

Second lot to be sown now!

[lettice]

It obviously does not too cold here but always sow sweet peas in outside pots mid January and they survived our two spells of snow and -3 to 0c low temps we had here in Feb and March. Always done that and had good strong crops, they seem hardy.
Do also sow in greenhouse mid march and they have caught up in size compared to the outside ones and ready to go out now, as four inches tall.

[juvenal]

Thank you for the advice, folks...