I am using Fox Farms Ocean Forest Soil. It has been filled half way up in the starter pot in case of leggy seedlings which I struggle with. My theory is that if the seedling is leggy, I can continue to slowly fill the pot with soil to allow more root growth nodes or whatever as it grows. Hopefully it allows for the root structure to grow as much outwards as it does downwards. Since the roots are closer to the bottom, we will see if that ends up being better or worse.