What am I doing wrong ?

Hello All 

Over the past few weeks I have been having real trouble getting my Brussels Sprouts (Seven Hills) to germinate.

I have started them in multipurpose compost in a plant pot witch is covered by half a bottle on a window sill but I have have seen no sign of them after 3 weeks this is my second attempt but still no joy.

What am I doing wrong ? 

Any Ideas or solutions would be appreciated. 

Thank you

Les