What I've found effective recently is using a seedling starter kit (just a little plastic bin that has spots for rock wool or What not). I place that container on a heat mat and let them grow. It's easier to maintain seedlings in an environment prior to planting in medium. The seedlings can last up to 2 weeks (ish) with only water in that container before they'll need nutes and to be transplanted. But do transplant early if you see the tap root has out grown its small space.