For seeds that need light. I do one of 2 things.

1-I always add a little substrate on top of seeds, VERY little, but remember light is getting thru a thin layer of substrate. Then I water them in well.

2-For seeds that may be put outside, I put my soilless mix in a container, add a layer of coarse grit, and deposit seeds on top of grit. I then water in. Thats it.

I have not started any of the seeds you mentioned, so someone else will have to chime in on that note.

Couple of other notes. Get those seed pots under lights (light isn't going to burn seeds), and I would keep the plastic over them.
Why are you adding extra perlite? I just use a good soilless mix, like Metro or Fafards. Many others out there as well.

Also, when I water initially after sowing the seed and covering with plastic...I never have to water again before seeing germination....even on a heat mat.

Thanks for the response, naturemitch.

I add the extra perlite only because several (online) gardening sources instruct you to to a half and half mix, to increase drainage (prevent water retention) but I suppose it's overkill, to an extent. I do seem to have a little more success rate when I do add more perlite, but I'm trying to be more conscious about not drowning the poor seeds when I plant. (Still making mistakes!) I have not seen either Metro or Fafards in the garden supply stores in my area (San Francisco). I checked Fafard's website, but it doesn't look like they sell them in California at all. Rats!

What kind of "grit" do you use for sowing? Are you talking about small gravel, chicken feed, sand, etc.?

You haven't had any germination from any of these seeds, right? What is the source of your seed? The only reason for what you describe is infertile seed or too low temperatures.

For seeds that ask to be surface sown, I do not suggest adding grit such as perlite. To do so risks seed to mix contact, especially when seed is not pressed into the mix. Covering with clear plastic to maintain 100% humidity is a must until germination. Al

Thanks for the advice, everyone.

ifraser25, I have considered this a possibility with my Alyssum seeds. They are a Botanical Interests pack from last year, which is a seed company I like and I usually get good quality seeds from. But it's possible the seeds are duds. I'll keep giving them a chance, though.

For a while I was worried that it's actually too warm for the Alyssum to germinate -- we've been having 70 degree weather here, and I think the seed packet mentions it liked cooler temps. But I will leave out the perlite from my mix this time and see if that makes the difference.

By the way, this warm weather has caused all my other seeds to EXPLODE with growth. I guess they were all waiting for that tiny extra rise in temperature.

Melody,
I think Violas seeds need darkness to germinate, so try covering the seeds a little instead of surface sowing them.

Art

Thanks Art, I think I did cover up the violas a tiny bit. The cold treatment worked, they've all peaked their little green heads out of the pot now! Just took a little longer than I expected.

My coleus, lobelia, thyme, and violas have finally germinated, hooray! The plastic baggie tent worked well. Only thing that hasn't sprouted is the Alyssum. I suppose those are a lost cause, now.

I sowed a mess of alyssum outside, in a pot. I know they're supposed to be a certain distance apart, but honestly, they're tiny seeds...I planted them in some soil (nothing special, I guess--potting soil?) and set them outside. All I've done is try to keep them moist. And I put netting over it to keep the cat out. Several came up. Alas, some of those that did got utterly bowled over in last night's storm. But there are some smaller ones that are OK because they weren't tall enough to get knocked down.

I also tried the same thing with some columbine this year. Nothing happened with them at all. So much for supposedly easy plants (at least, I think they're supposed to be pretty simple).