I use kelp meal from a local company.

I've also gone to the beach and grabbed out some kelp tuber thangs, brought them home rinsed the hell out of them, chopped them up finely with a machete, rinsed them a bunch again and mixed with some dirt for two months.

I layed the mix down and planted new lawn seed over it. Grass grew like weeds. Way better than the area without the kelp mix.

I think i'll try it on mary next year.