I sow in plugs or pots on my auto-waterer in my greenhouse, that keeps the compost wet, works very reliably.
I grew little gem because my OH used to buy little gem hearts, but I found they do take a lot of time to heart up, and there is a lot more loose leaf then the ones you see in the shops.
I don't think I am doing anthing wrong, as my plants look like the pic on the seed packet, so I assume shop bought plants are heavily trimmed.