growing wildflowers in a raised bed

hi guys - looking for some advice. I'm considering putting some wildflower seeds (well, bee friendly one's, but I guess the advice is the same) into a raised bed. I currently have one tomato plant one one side of the bed - but the rest is empty. I did consider putting another couple of tomato plants in the empty area - but decided against that as I'm growing determinate this year - and these tend to do better in taller pots, in my experience

I have a couple of queries

a) is it too late to plant out the wildflower seeds?

and 

b) around a month ago, I prepared the raised beds with lots of decent compost, manure and topped it off with mulch. everything I've read about growing these plants suggest poor soil is best. I did have a thought about topping the bed with a layer of seed compost and scattering the seeds on top of that. do you reckon that'd work?

I'm quite keen to get something going, but am wondering whether it's best to hold off til autumn

if that's the case - I guess I could lob a load of nasturtium seeds in to fill out the bed and add some colour

thanks in advance