Rocky soil? Grow grass using compost
Q: Should compost be applied to newly-planted grass seed as a top-dress on tightly-packed or rocky soil?
For a cool season grass like (tall) fescue, use a very light amount of compost (less than a 1/16 inch). Keep it irrigated.
Some composts (like McGill SoilBuilder) are more nutrient-packed than others. Be careful of the amount of nitrogen you are adding to the newly-seeded area. Too heavy a hand during nutrient application could burn or even stunt newly-seeded turf. The same is true for synthetic fertilizers.
For a warm season grass like Bermuda, an application of 1/8 inch to 1/4 inch over the next 30 days works. Remember to keep it irrigated. This will help the seed establish.
Most tightly-packed soil consists of clay, which challenges good porosity. Using a soil amendment like compost replenishes soil organic matter. Compost improves porosity, even in a rocky soil, and allows air and water to move through the soil more freely.
This creates an encouraging environment for turf establishment and survival.
Toss a little clover in with the grass seed to help set nitrogen and encourage bees.