Early this spring, I put down new sod. The grass looked incredibly
healthy for several months. But now, although it's still very thick,
the grass is starting to look yellowish. It's not underwatering, as I
know the gray-green tinge underwatering causes. I have not
fertililized the lawn since I laid it down (except for the starter
fertilizer). I cut the grass high at the mower's highest setting, and
use a mulching blade. (The mulched clippings are fine enough not to
be visible on the lawn.) I deep soak the lawn three times a week. I
feel like I'm doing everything "right" but still, it's looking
yellowish. Any suggestions?