I do nothing special for seedlings, except dust with a myco product. They start and finish in the same organic soil. Usually mix my own but Happy Frog has given me spectacular results in the past, and I can't afford the $150 to resupply my ingredients, so I went with it. 1 bag Happy Frog 5 gal perlite 4 cups tomato tone 4 cups GRD 2 cups kelp meal Cooked for 3 weeks. Never burns seedlings or clones. The only organic soil that has ever burned a seedling on me is Ocean Forest.
All I use is ocean forest, no fertilizer for 4 weeks, than I introduce fertilizer in the flowering stage