Water every hour
The back lawn was never really a lawn. This place was a new build, and what we were handed was clay with a skim of topsoil raked over it and some grass seed thrown on top. It looked convincing for about a season. Four years on it had cracks running right through it every summer, and the grass sitting on top had mostly given up trying.
So in December 2023 I dug the whole thing out by hand. Every piece of it. No hire gear, no contractor, just a spade and a lot of evenings breaking clay up into something that would let water through. Then we brought in new topsoil and spread it over the lot, which is the first time the back lawn has had anything underneath it worth growing in.
The seed went down on Tuesday the 12th of December: Elfin Tall Fescue, the stuff the sports fields use, because I was not doing this twice. Then came the watering. I printed a card and stuck it up so nobody could say they had not been told. Mow at 75mm. Water every hour. For the first fortnight that sprinkler was on more than it was off, and it worked. It came up thick and dark and it looked amazing.
You cannot grow a lawn on builder's clay and hope. I gave that four years to prove itself and it never did.