An understanding of nutrient needs of plants is important for maintaining healthy landscapes, and for making wise, environmentally sound management decisions. Applying too much fertilizer can lead to too much leaf growth, resulting in large amounts of turf clippings -- which are difficult to grasscycle -- and weak, excessive growth of landscape trees.
Sustainable Landscapes: Plant Nutrients and Fertilizers
Excerpted from “Become a Landscape Company Owner” by Janet Hartin (fabjob.com).
Diminishing resources and client demands have made Sustainable Landscapes extremely important. Water-wise (or Xeriscape) native plant material, best management practices and water-efficient irrigation systems are crucial components of sustainability.
An understanding of nutrient needs of plants is important for maintaining healthy landscapes, and for making wise, environmentally sound management decisions. Applying too much fertilizer can lead to too much leaf growth, resulting in large amounts of turf clippings — which are difficult to grasscycle — and weak, excessive growth of landscape trees.
There are 16 essential nutrients required by landscape plants, classified as either macro- or micronutrients. Micronutrients are just as important for plant growth as macronutrients, but are required in lower concentrations. Essential macronutrients not supplied by air and water are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S). Essential micronutrients are iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), boron (B) and chlorine (Cl).
Nitrogen is by far the most limiting nutrient required by landscape plants. Sources of nitrogen fertilizer are classified into two main categories — quickly available (fast release) and slowly available (slow release). As you probably guessed, the distinction refers to how soon the nutrients are available to the plant, and the length of time they remain available. Both quickly and slowly available sources of nitrogen fertilizer may be applied separately or in pre-packaged combinations containing other nutrients. So how do you know just what’s in a bag of fertilizer? Look at the product label and learn how to crack the code — it’s all there. The three numbers separated by a hyphen always stand for the percentages of nitrogen, phosphorus, and potassium (always in that order) contained in the bag. So, a bag that has “10-10-10” on the front contains 10 percent nitrogen, 10 percent phosphorus (P2O5) and 10 percent potassium (K20). Add it up and you get a grand total of 30 percent nutrient content. What happened to the other 70 percent? It’s all inert ingredients used as filler. That’s good, though, because otherwise it would be difficult to apply the fertilizer evenly.
Sources of nitrogen that are quickly available include inorganic salts such as ammonium sulfate (20-0-0), ammonium nitrate (34-0-0), potassium nitrate, and organic forms such as urea and methylal urea. They are highly water-soluble. In the west, ammonium sulfate is often the preferred quick-release fertilizer for general use because it can neutralize high pH soils.
Many sports field and parks maintenance personnel routinely apply fast-release nitrogen products due to their low cost and convenience. It is important to remember that although fast-release fertilizers result in a more immediate response than slow-release forms of nitrogen, greater skill is needed in their application to ensure that the correct amount of nitrogen is applied and to avoid uneven spread. And no more than one pound of actual nitrogen in a quickly available source should be applied per 1,000 square feet per application. That means that a 10-pound bag of ammonium sulfate (20-0-0) contains 20 percent nitrogen (4 pounds) and will cover 4,000 square feet of turf.
Slowly available nitrogen products cost more than quickly available products, but last longer so you don’t need to apply them as often. In many cases, they also lose less nitrogen from leaching and volatilization. Some, such as Nitroform and Hydroform, and natural organic products such as bone meal and activated sewage sludge need high temperatures and bacteria to activate, while others don’t. Coated urea products slowly discharge urea through cracks in the coating. The urea enters the soil over a two or three month period.
Slow-release products also have the advantage of not burning plants as often as fast-release fertilizers, and are great for use by entry-level employees who lack experience with fertilizer applications. Uneven application isn’t as risky. They are also easier to use when grasscycling, since flushes of rapid growth are easier to avoid.
Phosphorus is necessary for metabolic processes involved in plant growth and development. Deficiency symptoms show up as slow growth, stunted plants and purplish leaves. Potassium is important in water uptake and can increase drought resistance. Potassium sulfate provides sulfur in addition to potassium, and is often recommended in high pH soils to reduce alkalinity. Potassium deficiency symptoms include tip and margin burn on older leaves and slow growth.
Janet S. Hartin has served as environmental horticulturist for University of California Cooperative Extension in San Bernardino and Los Angeles Counties since 1984. Hartin specializes in sustainable landscaping issues such as irrigation scheduling, greenwaste management, and integrated pest management of woody plants and turfgrass. Hartin received her B.S. and M.S. degrees from the University of Minnesota.