One of the more challenging aspects of facilities management is the prevention of surface water runoff contamination from fertilizers. These very common landscape supplements are not regulated in the same way as are pesticides and are generally not part of established Best Management Practices (BMP) routines. What follows will be a brief general discussion of fertilizers and then some management suggestions to help eliminate some of the problems associated with fertilizers including the possibility of their entering into surface water runoff.

Fertilizers 101

Basically, fertilizers provide the “food” for plants to perform normal growth functions. Ideally, landscapes, when managed properly, can thrive in a more or less sustainable fashion, requiring little additional plant nutrition supplementation provided that the natural system for nutrition replenishment is maintained – allowing fallen leaves to remain, grass clippings to decompose, the use of mulch in flower beds, etc.

Plants absorb fertilizers from the roots and are transported throughout the plant where they are incorporated into the nutritional needs of the plant. The amount of fertilizer required by the plant is determined by the state of the soil surrounding it. Soils rich in organic matter and with the proper soil moisture can provide for the nutritional needs of the surrounding plants with little additional need for supplementation in most situations.

Plant Selection

Proper plant selection can go a long way to reduce or eliminate the need for fertilizers in the first place. In established landscapes, unfortunately, the facilities manager frequently inherits the choices of his or her predecessor. However, often times it may be possible over time to replace poor plant choices or a revitalization of a landscape takes place that would allow the facilities manager to make more “informed” plant choices to replace the existing landscape.

Many tropical plants commonly found in commercial landscapes are poor choices not just because of their nutritional and irrigation needs, but they are also attractive to plant insect pests, diseases or rodents.

In Appendix D, you will find a number of resources for suggested plant choices that are better suited to the southern California environment and meet the requirements discussed here. Certainly, the use of native plants and the use of xeriscaping (plants that require little water) should be considered as well.

Weeds and Fertilization

Turf areas that have low soil fertility can be attractive to many weed species that can thrive in those situations. Many of the invasive clovers can be seen thriving in otherwise healthy looking turf due to poor or inconsistent fertilization practices and are an indication of low soil fertility.

Irrigation and Fertilizers

Plants and turf that are water stressed or over watered can have a significant effect on plant health. This can often be mistaken for lack of fertilization. This topic is discussed in greater detail in the MANAGING WATER section elsewhere in this document. Fertilization will not overcome the problems associated with improper watering or other cultural practices such as poor soil drainage.

When to Fertilize

Fertilizer applications are best determined after closely examining the plants themselves. As long as woody plants appear healthy and show normal leaf size, color, and desired growth, they probably don’t need fertilizer. Soil testing for the concentrations of existing nutrients can be helpful in determining the need for fertilization and is suggested. If they are needed, fertilizers are usually applied at times of the year that coincide with traditional plant growth cycles which in most cases is the early spring in southern California. It is also recommended that fertilization take place as the growing season winds down in the fall. Because of the high use demands made on the plants, turf maintained for sports activity requires a much more intense fertilization regimen. Landscape trees should only be fertilized if outward symptoms are observed to warrant such a treatment. Advice on issues with trees in the landscape can be given by certified arborists or by contacting the County Plant Pathologist who can provide a determination on whether the symptoms displayed by trees (or other plants) are caused by nutrient deficiency or some other casual factor.

What Fertilizer Should I Use?

What you should use, or, more likely, what you should ask your landscape vendor to use, would seem to be a very basic question. Since one of the concerns about fertilizers is potential surface contamination of runoff due to rain or irrigation, it is very important to use nutrition supplements that are not going to lend themselves to be easily moved offsite via runoff. In general, slow release organic fertilizers are less likely to enter stormwater. However, many organic fertilizers are very bulky due to their low concentration of nutrients and can have other drawbacks such as unpleasant odors or salts associated with them. Slow release chemical fertilizers allow nitrogen to become available over longer periods of time, so they don’t need to be applied as often and are often the best choice to prevent surface water contamination.

Fertilizer Do’s and Don’ts

Okay, so we’ve decided to make a fertilizer application or have a vendor do so. Here are some good practices to incorporate into our work plan to prevent the fertilizers from moving offsite:


  • Fertilize only as needed and only after problems have been eliminated as the cause of poor growth
  • Use a soil fertility test or some other acceptable method for verifying soil nutrient deficiencies
  • Use a slow release, organic fertilizer
  • Make sure that the application is made so that routine irrigation will not create runoff
  • Read and observe pesticide label precautions about storing with fertilizers
  • Dispose of unwanted or unused fertilizers properly
  • Minimize storage of fertilizers by buying only what is needed



  • Apply fertilizer based simply on a calendar schedule
  • Apply fertilizers within 24 hours of anticipated rain or on windy days
  • Make applications of fertilizers within 5 feet of pavement, 25 feet of a storm drain inlet, or 50 feet of a water body
  • Store pesticides and fertilizers together without checking the pesticide label