Bringing this to the top, cos I followed the link given in The Shed and think it's gonna be sooooooo useful to new members or those, like me, who printed it out first time round - and now can't find it, so thanks Mike for the original work.
I don't have heat in my greenhouse, so outdoor toms, etc. get started off in the house /bout mid-end Feb then grown on in my cold frames/greenhouse until ready to plant out. Stuff like french/runner beans get started off in pots in the cold frame march-time. Too many damned squirrels round here to faff about sowing in the open ground & covering with netting. >:(
Chart says outdoor toms can't be planted directly outdoors, tho? Some of my thinnings - 1st leaves & hair root only, got thrown with other stuff onto the compost heap or dug into veggie beds - where they grew and grew and fruited beautifully ;D