Fertilizing Responsibly

If you choose to fertilize your lawn, follow the tips below to help minimize your environmental impact on the St. Johns River.

Click here for a complete list of our River Friendly Yard recommendations.

Read it before you feed it.

Carefully read the label on the fertilizer bag. You will find three numbers: the first number is the percentage of Nitrogen (N), the middle is Phosphorous (P), and the third is Potassium or Potash (K). Select a slow-release nitrogen fertilizer with little or no phosphorous that does not contain herbicides or pesticides.

Slow it down.

Select a fertilizer with the highest percentage of slow-release or water-insoluble nitrogen that is available (50% or more is recommended). Slow-release fertilizers are less likely to leach out or wash away in runoff. This information can be found in the “Guaranteed Analysis” section on the back of the bag.

To determine the percentage of nitrogen that is in a slow-release form, divide the percentage of “slowly available nitrogen” by the amount or percentage of total nitrogen in the fertilizer. For example, a fertilizer with 15% nitrogen and 7.5% “slowly available nitrogen from sulfur coated urea” would mean that (7.5/15 = 50%) 50% of the nitrogen in the fertilizer is slow-release.

The Phosphorous (middle number) should be no more than 2. Our North Florida soil usually has enough phosphorous, so we generally don’t need to add more to our lawns. If you just want your lawn to be greener, you may only need to add iron.

Consider using an organic fertilizer.

Organic fertilizers are slow-release and add organic matter to the soil. Organic matter helps to retain moisture and nutrients, meaning you have to water less and use less fertilizer.

Avoid fertilizers that contain weed killers.

Treat only the affected areas for weeds and insects and use nontoxic alternatives whenever possible. Consider pulling weeds by hand. Corn gluten is an excellent alternative pre-emergent and fatty-acid soap products can be effective broad-spectrum herbicides.

Establish a fertilizer-free and pesticide-free zone.

Do not apply fertilizers or chemicals within 10 feet of waterways or adjacent to impervious surfaces, like a street or driveway.

Less is best.

When using a fertilizer with 50% or higher slow-release nitrogen (N), you can apply up to 1 lb. of nitrogen (N) per 1,000 square feet per application. (In other words, no more than .5 lbs of soluble N/ 1,000 sq. ft.) We suggest the University of Florida IFAS Extension’s basic, low-maintenance recommendation for St. Augustine grass, fertilizing twice a year during the growing season (early April and late September). Click here for a link to UF IFAS Extension recommendations for fertilizing different types of turfgrasses. You can green your lawn during the summer by applying Iron (Fe) in the month of June.

Never apply fertilizers before heavy rains and approaching storms. Avoid application of fertilizer during the rainy summer months when it is more likely to leach or runoff into our waterways.


All fertilizers and chemicals can potentially harm our waterways. Please, use sparingly and with caution. St. Johns Riverkeeper does not promote the use of fertilizers or lawn chemicals and does not endorse any specific lawn care products.