I haven't posted here at ATP much, but this topic caught my interest. So I thought I'd share my experience in hoping it will be helpful to others. I've been sowing in vermiculite for about three (3) years now. I don't recall getting that information from here or DG, but I do know what started it. I also had those terrible little clear tender root-eating worms. Those are fungus gnat larvae. They were wiping out my seedlings. They love the bark/peat potting mixes ... and tender roots! After much internet search, and what others had tried, I tried using the mosquito dunks (sorry, I can't think of the name of the actual stuff), and although others had raved about it, it certainly didn't help me. Somehow I started sowing in vermiculite and my fungus gnat problem is pretty much gone.
I use small styrefoam containers to start my seedlings (these are the ones restuarants use for carry-out dressings). I enclose these in sandwich baggies until the seeds start germinating, then I remove the baggie. So I've never left them as humidy domes of a sort. I overhead water because the containers tend to want to float if I try to bottom water. It is difficult though to know when they are dry enough to need water, but I have learned by the feel of the weight of the cup when water is necessary, or sometimes the seedlings just tell me by their wilt.
After germination, the seedlings are generally in the styrefoam containers for 3-4 weeks (sometimes longer which hasn't been a problem for perennials). I like them to get some pretty good roots going before transplant. The one thing I really appreciate about the vermiculite is that the roots are so much less tangle free than in potting mix where I fought to get them apart and tear up the roots, the roots growing into the bark. I usually then pot up the seedlings to 3-cell packs or the small 2" containers, using a good potting mix containing light fertilizer. If fungus gnats should come, I have found that the seedlings then have a good enough root system before the larvae hatch that they are able to withstand the chewing on their roots.
I start the seedlings indoors, and use the small styrefoam containers for lack of space. I try to time it where shortly after transplant, the seedlings will be able to go outside to a sheltered location.
