Posted: 16/10/2017 at 19:28
If it is a build up of thatch, then it will need scarifying using a metal lawn rack and areating using a garden fork to create holes for improved drainage and air flow to the root system. But in a new lawn I would be surprised that this would be required. If the new lawn was of good quality without moss or weeds and the ground work was effectively carried out preparing the soil prior to laying the lawn - removing or large stones and racking and treading down the lawn to create what is called a fine tilhe. Personally, I would do the thatch removal in spring if it is the problem and your new lawn needs time build up it root system
Feeding a new lawn at this time of year will make it grow and create new swords of grass that well be effected by possible ground frost. If you fertilised the ground work prior to the new lawn been laid with Growmore then that would be sufficient for this time of year to establish the lawn.
Grass, like any plant, will become dormant when the temperature drops and a feed on a new lawn would be not beneficial due to this