Posted: 18/09/2016 at 12:59
It's a cyperus, possibly Cyperus eragrostis. If you have lots of it in your garden that probably answers the second question, though it doesn't seed much here, I lost it and had to re-introduce it. I think it's too dry in my garden, most of the successful ones are in the damper areas.
Yours looks a bit dry and yellow as well