Posted: 10/03/2016 at 17:12
First week of June to make sure. It really depends what you're growing though. Most years, hardy annuals will be fine sown outside in April, but you have to look at your own conditions - if the ground's soggy and cold, they may rot.
I only grow toms undercover up here - our temps are too low at night. I start them in March, and by the time they're too big for windowcills, it's usually fine to get them outside undercover.
Anything that needs starting undercover can usually be sown in March, but it depends what facility you have for hardening off, cold frame, greenhouse etc., as you can easily run out of room. That's the issue you seem to be experiencing just now!