Maintenance I: Fertilizing your garden

Proper maintenance of your water-conserving garden is very important to ensure optimum performance from the garden.  However, proper maintenance does not have to be labor-intensive.  In fact, gardeners often tend to over-fertilize in a traditional garden.  Properly maintaining your water conserving garden will result in fertilizing less often, and with less fertilizer, which will keep your plants healthy but will not necessarily encourage growth at all times.

In general terms, fertilizers usually are divided into two main categories: organic and inorganic.  Organic fertilizers are derived from animal and plant sources, or synthetic materials composed of carbon-based structures.  Organic fertilizers generally are not soluble in water.  Instead, they depend on microorganisms for release, and thus release nutrients more slowly.

Inorganic fertilizers are derived from mineral sources.  They are highly soluble and release nutrients very quickly, but have a higher fertilizer burn and leaching potential.  Leaching is the movement of fertilizers in the soil below the root zone.  Leached fertilizers are wasted and may find their way to the groundwater, where they might have adverse environmental effects.

Inorganic fertilizers are best used on plants showing a nutrient deficiency because they release nutrients rapidly and uniformly.  Organic fertilizers release nutrients less uniformly and more slowly, and therefore need to be applied less frequently.

Fertilizers come in liquid or granular form.  Granular fertilizers also come in slow release types. If available, use fertilizers that provide nitrogen in slow-release form, such as sulfur-coated urea, urea formaldehyde, IBDU (isobutylene-diurea) or methylene urea.  Slow-release type fertilizers generally cost more than soluble all-purpose garden fertilizers, such as an 8-8-8 or 10-10-10 (the percentages in the ratio represent nitrogen, phosphorus, and potassium, respectively), but they last longer since they release nutrients at a slow rate.  Slow-release fertilizers are derived from natural, synthetic organic, or coated materials, and may require microbial, chemical, and/or physical breakdown.  The advantages of slow-release fertilizers are that nutrients are not made available to the plant all at once, thus reducing the risk of fertilizer burn; and that fewer applications are needed, thus reducing the risk of leaching or pollution to the groundwater.

In a water conserving landscape, use a low-nitrogen fertilizer.  Nitrogen promotes rapid growth – not what you would want because more growth means a greater need for watering.  Also, over fertilization reduces root growth in favor of shoot and leave growth, thus reducing the overall drought resistance of a plant.  A low-nitrogen fertilizer with a 5-10-10 or a 2-10-10 ratio is recommended.

Use fertilizers when you want to encourage growth, but note that this will increase your plants’ water-use and pruning requirements.  Keep your plants healthy, but do not encourage growth at all times.  

The upcoming article of this series will discuss fertilizer application guidelines.

This article is part of a series of articles prepared by the Center for the Study of the Built Environment (CSBE) on water conserving landscapes.  

For additional information on water conserving gardens, visit the CSBE web site at www.csbe.org

Support for the CSBE project on water conserving landscapes is provided by WEPIA (Water Efficiency and Public Information for Action), a program being implemented in collaboration with the Ministry of Water and Irrigation and funded by the United States Agency for International Development (USAID).