Posted: 18/11/2016 at 00:30
Are you sure you were using a good seed merchant? Some of them should be ashamed of their germination rates even though there are statutory percentage germination rates for vegetables.
You might be better off not trying to grow anything in a shed or attic, grow-lights or not. What most seeds need is warmth to start them off. LED lights are cold. Have you thought of a cheap propagator?