Yes, grass does germinate between the plugs because the plugs break down and that soil contacts the seed. And remember, I'm slit seeding too. I try not to seed in the spring due to weed competition and it can be difficult to get the new grass through the summer. Unless the lawn is irrigated there's a pretty good little to none of it will make it throught the summer without dilgent watering efforts by the homeowner. However, I have an account that I'll be seeding in the next week or two because they have a lot of turf damage from tree work done as a result of Hurricane Sandy...skid steer, stump grinder and tree impact. It's the customers wish to get the lawn repaired now, even if it means seeding again in the fall. As it is now it wouldn't even be mowable without repair.