first off first thing is ph u have to have that in ck.atleast close,if you just found this soil then you don't know what is in it.looks to me like the soil could be a bit hot"to much nutes for a seedling".as you just found it that means it could have been mixed for a much older plant.in which your case will burn those lil babies up.anyways go get sum fresh clean soil from the store.and you def need to ck ph run off b4 you plant seeds.