I've just laid (2 pallets) new St. Augustine Raleigh grass in 1/2 of my yard. I know I can't mow it with a mower since it will pull it up but I've been "mowing" with a weed-eater to keep it even with the rest of the lawn (non-replaced, normal weekly mowing). The sod seems to be growing fine but I'm obviously trying to blend it into the already existent lawn.

It's getting plenty of water all over but am I slowing the growth of the new roots in the sod by mowing it or am I helping it to grow by "telling it to" by mowing?

Seems like it would encourage growth since the plant knows it needs new surface area (leaves) to absorb sun, but I can also see where it might hurt it because it's not getting enough sun to adequately grow roots to knit into the already stable lawn.

Thanks in advance.

let it be for a while, let it become established on its own. water it weekly (or whenever the 1st inch or so of soil is dry) and fertilize it very lightly after a month or so, increase fertilization after several months.

Grass has about a 1 month cycle to grow flower and seed. By mowing it you are telling it to grow the leaf. Too much watering does the same thing. There needs to be a balance between mowing and watering. If the grass finds it easy to get nutrients then it will put it's energy into leaf. Just like after you fertilize. If you water conservatively then it will share growth between leaf and roots. Roots are the most important aspect of grass when it's new. I would would water about a half inch per week and let nature do the rest.

Good luck!