I'm in the middle of creating a raised bed and have mulched part of it with the perennial plants that I have planted. I'd like to sow seeds directly into a secondary raised bed in the middle of my larger bed (cockscomb and alyssum together). Because everything is mulched, it will look better if the raised bed is mulched, but I'm worried that the seeds won't germinate and the seedlings won't grow if I put mulch on after sowing.
Would it be inadvisable to mulch after direct sowing these seeds? If so, is it inadvisible to mulch after direct sowing *any* seeds or only very small seeds?
I'd wait until after the seedlings sprout and are big enough that you can mulch around them. One of the reasons why people mulch is to help block weed seeds from sprouting, but unfortunately it'll have a similar effect on your desirable seeds. If it's a tough plant and you have a lot of seeds, chances are some of them would make it up through the mulch, but you'll have better success without it. And I'd avoid mulching until the seeds come up regardless of the seed size, I don't think that would make a difference.
If I have a large area and want to keep the weeds down while my seeds are sprouting, I mulch first then clear small areas to plant the seeds in. That way, weeds are controlled in most of the bed and I only have the small areas I've cleared to plant seeds. Just a little circular area is enough to put two or three seeds in each area. Even with my mulch being 2 inches, the seeds get plenty of light to grow. It's a little extra work but less than weeding!