Horticulturist urges slow‑release, potassium‑only fertilizers to reduce nutrient runoff in Florida

Steve Davis, a horticulturist who identified himself as working for the Department of Water Resources and the Water Conservation Department, advised homeowners and landscapers to choose slow‑release and potassium‑only fertilizers to limit nutrient pollution in Florida’s sandy soils.

Davis said, “Slow release fertilizer is the fertilizer I recommend most often,” explaining that sandy soils have limited ability to retain applied nutrients, which means nitrogen and phosphorus “quickly move through the soil” and can be lost to the aquifer or washed into surface water bodies.

He described the numbers on fertilizer bags as the macronutrients — nitrogen, phosphorus and potassium — and said phosphorus is plentiful in native soils: “Phosphorus is plentiful in our native soils, so … the phosphorus should be 0.” Davis advised consumers to look for formulations with little or no phosphorus where soil tests show adequate levels.

On timing, Davis recommended applying a high‑potassium, potassium‑only fertilizer in October, citing potassium formulations such as 18 or 22 as his typical choices. He said a potassium focus in the cool season does not spur the surge of growth that late‑season nitrogen can cause.

He warned that late applications of nitrogen can encourage new growth that is vulnerable to cold snaps: “Applying nitrogen late in the season often encourages growth… and that can significantly injure your lawn” if a freeze occurs after a warm spell.

The comments were technical guidance rather than a formal rule change; no vote or regulatory action was recorded. The presentation highlighted simple, garden‑level steps — choosing slow‑release products, minimizing phosphorus where soils are already high, and avoiding late nitrogen — as practical measures to reduce the risk of nutrient runoff into groundwater and surface waters.