soil Soil Too Light

[spicymeatball]

Last year I tried a new organic potting/starter mix. It is mostly peat moss, and also has vermiculite, perlite and mychorizae. the mix was so light that it dried out very quickly because of the heat, even under the dome. I ended up killing all my seedlings last year. 
 
Normally I would go outside to the compost pile to get some material but the ground is still frozen and covered with snow.  Lots of snow. What is the best way to put some weight into the mix?

 

[Weed]

I want to say water...
 
Sounds like you used Pro-Mix BX?
 
If you want to add more water retention you need more (fine) verm or more peat.
 
Some of that Jiffy Seed Starting mix will add both, or you could just use that in lieu of the other mix.
 
I'm curious how anything dried out under a dome though.

 

[spicymeatball]

 It's not a completely tight seal on the dome.  But the room was warm and dry from an electric radiator. It dried out sooner than I expect. And this year I'm not planting them at home so I need the soil to hold over in case I can't get there.

 

[juanitos]

having a well draining mix (too light in your opinion) is actually a desired trait, means your roots get more air, and don't have damping off.
 
It might be better to just set up some kind of automated watering say dripline + water timer.