NOTICE: Should you cover your seeds with soil or not?
This is an excellent question and as you'll notice in the Microgreens Kit seeding videos I don't cover my lettuce seed with soil during the germination process. This is intentional as lettuce germinates better WITHOUT being covered with soil.
That being said most other seeds do better with a small covering of soil over them. You'll notice in the DIY videos below that I cover the peas with a small layer of soil for germination.
I believe you can leave other small seeds from other plants such as kale, cabbage, etc. without a soil covering for germination just make sure to cover your tray with a plastic bag or another tray or something to keep it dark and humid inside while the seeds are germinating.