Do not put top soil over grass seed, but you can add a thin layer of organic matter to help the seed to germinate.
‘Never put topsoil over newly planted grass seed,’ says Yamaguchi. ‘This won’t provide healthy growing conditions – it will actually prevent the seedlings from sprouting by essentially suffocating them.’
‘Leaves, straw, and peat moss can be used to help hold moisture for the seed to germinate and grow,’ adds James.
Once the grass is more established then 'top dressing is something you can do a couple of weeks after fertilizing a lawn if you’re really keen for your grass to grow. Mix together materials like sand, soil loam and peat and apply this to your dry grass. The materials will transfer nutrients back into the soil and promote growth,' says Chris Bonnett.