Prescription Fertilizers for Trees and Shrubs Notes to the PowerPoint Presentation Desert Green 2013 Robert Ll. Morris, Emeritus University of Nevada [email protected] Desert Green is a conference held annually in Las Vegas for landscape professionals. This is a copy of my presentation on PowerPoint and my notes for the presentation. Slide 1. Title slide with contact information. Slide 2. Characteristics of desert soils. Desert soils contain very little organic matter and they are chemically and physically undeveloped. Because they contain so little organic matter in them, they have very little structure or are structureless. For this reason they sometimes tend to drain poorly. Their alkalinity or pH is normally high. Frequently they contain high levels of salt of all different types. If these soils have never been developed, they can change rapidly both physically and chemically when water is applied to them. Slide 3. There are 16 or 17 nutrients that are essential to plants. Several of these are needed in large amounts and we call these major elements or macronutrients. The rest of the nutrients are needed in a much smaller amounts, still just as essential. These are referred to as minor or micronutrients. All of these nutrients are essential to plant life and if any one of them is missing, the plant will die. If any of these are insufficient for the plant, it can display visual symptoms, poor health and subject to increased disease and insect problems. Bags of fertilizer traditionally contain nitrogen, phosphorus and potassium if they are a complete fertilizer. These three nutrients are called NPK and their relative amounts determine the fertilizer ratio. Carbon, hydrogen and oxygen the plant obtains from air and water. Most desert soils contain adequate amounts of calcium, magnesium and sulfur. Of the minor elements, iron, manganese and zinc can be in short supply to plants because of the soil’s alkalinity or high pH. In most desert soils were landscape plants are being grown, nitrogen is most commonly found in the greatest need by plants. Second to nitrogen is probably available iron. Slide 4. The three numbers on the fertilizer bag give an indicator of the amount of nitrogen, phosphorus and potassium contained in the bag, in that order. Sometimes there is a fourth number present. Although not legally required it usually represents the amount of sulfur contained in the fertilizer. The fertilizer ratio tells us the relative amounts of NPK. For instance, if the fertilizer has a ratio of NPK of 3:1:2 then fertilizers such as 12-4-8 and 21-7-14 would represent this ratio. Slide 5. Although all nutrients are needed for a plant to live, nitrogen represents the one nutrient that is universally in short supply. Nitrogen helps to drive plant growth and causes increases in size. It stimulates increased leaf and stem growth, causes a darkening of leaf color, hastens plant growth after winter dormancy and helps to increase the amount of food manufactured by the plant. If applied too late in the year, it will decrease a plant’s hardiness to freezing temperatures. Most nitrogen fertilizers are pure white in color. Most nitrogen fertilizers dissolve easily in water and moves readily through the soil with irrigation water. Slide 6. Lack of nitrogen shows up in plants as slow growth, foliage with a light green color and a lack of density in the canopy. Slide 7. In pine trees a lack of nitrogen shows up in the same way. This translates to a canopy which is not full, small candles and needles occupying the ends of branches while most of the branch is without needles. Slide 8. If too much nitrogen is applied, plants might grow rapidly with an extremely dense canopy and very dark color. When nitrogen is applied in large amounts it can cause scorching to occur on leaves and tip dieback on needles. In some cases it may cause plant death. Applying too much nitrogen is a waste of money and causes environmental problems as well. Slide 9. Adequate amounts of phosphorus is most closely related to good root growth and plant establishment, flowering and fruit production, seed and oil production. When soils are cold and wet this can lead to a lack of phosphorus taken up by plant roots. There is a quick recovery by plants as soon as the soils begin to warm. Phosphorus fertilizers are typically dark in color, usually dark gray or brown. Slide 10. Unlike nitrogen, phosphorus can stay present in the soil for long periods of time, does not dissolve easily in water and does not move through the soil unless the soil is very sandy. Phosphorus levels can build in the soil with repeated applications of high levels. In some cases phosphorus can build to toxic levels with repeated applications. Phosphorus can interfere with other nutrients, iron in particular. Over application is a waste of money and can lead to environmental pollution. Slide 11. Deficiency of phosphorus can sometimes lead to purple discoloration of the plant which disappears when phosphorus becomes available again. This is very common to many plants in cold, wet soils. Slide 12. Potassium is sometimes underappreciated in fertilizer applications. Deficiencies are hard to see since a deficient plant gives no outward symptoms. Potassium chloride, a common potassium fertilizer used in mixing fertilizers together, as a reddish-brown color. Slide 13. Over applying potassium usually will not harm anything and it does not build up in the soil like phosphorus does. Deficiencies of potassium can lead to a plant’s decreased tolerance to stresses such as heat, cold, freezing, disease and others. Slide 14. Nutrients needed in smaller amounts. Of the seven nutrients needed in much smaller amounts, iron, manganese and zinc are the ones most likely to be in short supply for plants growing in alkaline soils. Of the three, iron is by far the one found most efficient in plants. This is odd because iron is one of the most abundant minerals on earth. The key to its limited availability to plants is the pH