Why do turf winterguard (applied late fall) fertilizers have no “P” (phosphorous)?

Question

A leading brand's fall food is 32-0-10.

As I understand it “P” helps roots grow. The fertilizers say they help grow deep roots.

So at first glance seems odd to exclude this macro.

My hypothesis is that phosphorus is mainly helpful at germination and early stages? So if your just feeding your mature lawn no need for this. Plus it's applied generally when temperatures are too low for germination. And we don't want phosphorus to not get absorbed and run into waterways?

Am I correct?

Answer 1

Your hypothesis is pretty much correct. In Wisconsin, at least, Phosphorus is (theoretically) banned from all fertilizers except those used for starting new lawns, precisely for the reasons you used above (P is not generally needed for mature lawns and excess P runs off into our streams and lakes). Most of Wisconsin's soils are heavy in Phosphorus anyway, so it's rarely needed at all.