All the nutrition a plant needs during the short time started in vermiculit is contained in the seed. That said, they should be transplanted out before they get their first true leaves (I believe).

Also, how long do you allow them to grow in vermiculite before you transplant to a larger container with soil in it, or into the garden?

Like sinfonian said, IMHO first true leaves. I personally start in seed starting mix for a margin of error.

Dan

Best bet is to use some loose potting soil...drop the seed on top of this...THEN cover the seed with some vermiculite. This way the seedling doesn't have to fight the soil.

IMO, vermiculite is a less than stellar choice for starting seeds. It collapses/compacts very quickly when top-watered with anything other than mist, causing it to hold too much water and remain saturated, robbing seeds of much needed aeration - and it's pH covers a wide range (from about 6.0-9.0), but it is usually mildly alkaline.

Seeds will appreciate something that is sterile (to prevent damping off fungal problems) and reliably holds lots of air. Sphagnum peat, because of it's low pH is, practically speaking, sterile. Peat mixed with either sterile Turface or calcined DE (NAPA Floor-Dry) @ 1 part peat:5 parts Turface or DE is a great seed starting mix - and it will not collapse. Fill cell packs with this mix and you can allow seedlings to establish to the point that transplanting is a breeze.

Al

I'm wondering that myself. I have seeds poking up in my vermiculite. I bottom watered them like in the SFG book, then I sealed it up in a plastic bag until they started sprouting. Now i have them in a bit of water so they don't dry out before I transplant them outside. The SFG book recommends to "transplant your seedling as soon as the first true leaves appear....The smaller a plant is the least shock it will undergo from being transplanted." But as for experience, I wait until the plant gets about 1-2inches high, that way I can handle it without breaking the leaves off or pinched the stem to much. But if you do the vermiculite thing (it is really easy), bottom water it.