when to plant sweetpea

I bought some sweetpea from my garden centre yesterday, they are about 3 to 4 inches high. Ive got them in my cold frame at the moment. When can I plant them out? :WINK1:

 

They be happy being planted out, but personally I would wait until the soil has a bit of warmth to it.

If you have a single pot with about 10 - 20 seedlings in it my suggestion would be to separate them all out and pot them up individually, give them 2 - 3 weeks and then plant them out. They'll be fine in the cold frame - open it during the day, particularly if the sun comes out.

Once they have 3 or 4 leaf-sets on them pinch the tops out so they bush up.