Phosphorus is one of the essential elements for plant growth, but in
excessive amounts, it can be toxic for plants. This is a case of too much
of a good thing being bad. The amount of Phosphorus in most fertilizers is
sufficient in most areas.
Because of the amount of Phosphorus that naturally occurs in the soil
varies from place to place, I would recommend having a soil test before
adding any amount of Phosphorus over that contained in said fertilizers.
In the area around Lexington, KY, there is so much naturally occurring
Phosphorus in the soil that adding more Phosphates could cause trouble in
the garden. The soil around Dunnellon, FL is so rich in Phosphates that
they used to mine it here. In fact, mining the stuff is how Dunnellon
first came to be.
So, I still have to be careful with my fertilizers.
Mark A. Cook
Dunnellon, FL. (Former mining boomtown)