Home Grown Rocket... and Moss

This was the first of the rocket I grew this year, picked in July (it's a really peppery one, tastes great)! I've been sowing seeds in an old Belfast sink in the back garden - which also has a Wisteria in it - and it's grown well... but so has quite a lot of moss. I think the moss must have been present in some recycled earth I used to fill the sink originally because the drainage seems ok and it gets the sun. So I just picked the last growing rocket leaves and plants and removed the moss and a layer of soil. Topped it up with a soil and compost mix. Will see if that does the trick.