JoAnne Skelly: Know your fertilizers

People use many fertilizer products to achieve a picture-perfect landscape and a high-yield vegetable garden, often without awareness of what is best for their plants, their soil or the environment. Timing of application and amounts of fertilizers are important because if applied in excess, they can be leached into groundwater and pollute our waterways.

The three major nutrients plants need are nitrogen (N), phosphorus (P) and potassium (K). Nitrogen supports plant growth, making plants green and leafy. Too much nitrogen can make plants grow too fast and become leggy. It can interfere with flower and fruit development in veggies such as tomatoes and cucumbers. Phosphorus supports root, flower and fruit development. Too little phosphorus may cause stunted growth and reduced yield. Potassium is required for overall plant development.

Plants need other nutrients in smaller amounts such as magnesium, calcium, sulfur, iron, manganese, zinc and others. Nevada soils aren’t usually deficient in these unless the soil pH is outside the optimal range for most plants (5.5 to 7.5) or a soil is extremely sandy.

Fertilizers come in many forms. They might be liquids, granulars or soluble powders. A “complete” fertilizer contains nitrogen, phosphorus and potassium. An “incomplete” contains only one or two of the major nutrients. A “balanced” fertilizer has equal proportions of the three. Fertilizers, by law, have a code on the label that tells you the relative proportion by weight of nitrogen, phosphorus and potassium, in that order. If there is a fourth number, it represents the percentage of sulfur (S) in the fertilizer. Other nutrients are indicated in parentheses after the N-P-K-S number, or in the complete analysis in the fine print on the label.

Fertilizers can be natural organic or synthetic inorganic. Plants take up their nutrients in the inorganic form, so the source of the nutrients does not matter to the plant. However, organics also help build overall soil health, structure and water-holding capacity, something inorganic fertilizers don’t do. Organic fertilizers are released slowly over time and are less likely to leach into groundwater. Organics have lower concentrations of nutrients than synthetic fertilizers. Inorganic fertilizers can be quick or slow release. Rapidly released nutrients are best applied based on the results of regular soil tests.

For more information, read Dr. Heidi Kratsch’s publication, “Fertilizing Your Vegetable Garden,” available at www.unce.unr.edu under publications. Your local Cooperative Extension office can provide a list of soil-testing labs.

JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.