I too used to think grass needed a higher temp of about 10 c to grow but I was surprised to learn that grass does indeed grow at 5c. maybe not vigorously but it grows. My own lawn has not stopped growing throughout this winter and even in balmy Cornwall we have often not had temps much more than 5c. I agree with discodave about feeding too but only after watering a couple of times. Anyway, good luck Steve5 but I'm sure your lawn will look great in couple of months.