Bedding plants

I have been growing bedding plants for over 40 years and i never put anything out till the 16 may
Tony

Not long to wait then Tony...

It's hard to generalize about bedding plants as they are almost as diverse as veg plants
Some are so hardy that they overwinter ( I've seen alyssum and antirrhinum in flower outside weeks ago ) so long as they are properly hardened off they can be planted out in April without problems.
The most sensitive ( To cold ! ) might be begonia and impatiens

Most of mine are now outside, but in a sheltered suntrap within an urban microclimate (I know that sounds daft to say of Didcot, but between the power station and the high building density, this part of town is normally a couple of degrees warmer overnight than the top of the hill, and can be four or five degrees warmer than the open fields!).  There's nothing in the exposed part of the garden that's not hardy, and won't be until I get some windbreaks up.