What is a safe distance from private drinking well to fertilize a garden?

Answer 1

Most common garden fertilizers are safe to use even directly over the well area. This is because most of the components of the fertilizer are not mobile within the soil. This means that at the molecular level, the particles of fertilizer attach themselves to clay particles within the soil, and thus are unable to move any deeper than tilling depth. The one component you need to watch is the nitrogen component, because some formulations of nitrogen will move down through the soil profile. If your fertilizer has an ammonium-type formulation of nitrogen, and you fertilize to only the level your garden needs, then even that will not move down to the level of your well.

The amount of nitrogen in your fertilizer is indicated by the first number of three on the label. Thus, a 32-16-9 fertilizer is 33% nitrogen. The "analysis" part of the label will tell you what kind of nitrogen it is, whether ammonium or nitrate. Nitrates are somewhat mobile within some soil types, especially if they are over-applied.

Additionally, some soil types simply do not allow nutrients to leach down through the soil at all. Heavy clay-type soils are a good example of this.

If you still have concerns, 50 feet is a safe distance from any potential contaminant. I am unaware of any contaminent of any type that can move 50 feet sideways through the soil. Surface runoff must be considered as well, since that can move much greater distances very easily.