What is a Balanced Fertilizer?
(Bill Argo sidebar in MSU Fertilizer article June 2003 AOS Orchids magazine)

http://www.growinhydro.com


A balanced fertilizer formula is important for growing any plant, including orchids. Balance does not necessarily mean equal (i.e., 20-20-20). A balanced fertilizer supplies a correct ratio of all nutrients in adequate amounts for normal growth. Once a sufficient amount has been supplied to the plant, there is no benefit to adding extra.



Take phosphorus for example: Fertilizers that have high phosphorus levels (bloom builders) can increase flowering, but only when a plant is phosphorus deficient to start with. If phosphorus levels are adequate in the plant year round, then adding extra phosphorus will not help.



To have a properly balanced fertilizer, you first need to understand what nutrients need to be supplied. There are 15 essential plant nutrients. These are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, zinc, copper, boron and molybdenum.



Because carbon, hydrogen and oxygen come from the air, it is the remaining nutrients that have to be supplied by the fertilizer. When you look at a bag of fertilizer, the numbers you see represent the percentage of only three nutrients: nitrogen, phosphorus and potassium. You usually have to look much more closely at the label to see what other nutrients are also being supplied by the fertilizer.



The second thing to understand is that both the fertilizer and the water can supply nutrients to the plant. Water is usually not a source of nitrogen, phosphorus or potassium, but it can be a significant source of calcium and magnesium (which are also needed by the plant for healthy growth). For example, at Michigan State, the well water contains about 100 ppm calcium and 35 ppm magnesium. Because they are already in the water, the Well Water Special only contains a small percentage of calcium and no magnesium. In comparison, RO-purified water (or rainwater) contains little calcium or magnesium, so it needs to be supplied in the fertilizer. The RO Special contains relatively high levels of calcium and magnesium to compen­sate for the lack of these nutrients in the water.



Finally, substrate pH plays an important role in the health (and flowering ability) of the plant. Two important factors that influence substrate pH are the fertilizer and the water. Fertilizers are termed acidic or basic because of their potential to raise or lower the pH of the substrate after it is applied. A good indication of how acidic a fertilizer is depends on the percentage of ammoniacal nitrogen and urea nitrogen (acidic nitrogen) contained in the formula. Many of the Bloom-Builder- and Orchid ­Special-type formulas contain anywhere from 50 to 100 percent of their nitrogen in the acidic form and, therefore, are acidic fertilizers.



With water, the important term to know is alkalinity, which is a measure of the acid-neutralizing capacity of the water. It is the balance between the acidity of the fertilizer and the alkalinity of the water that affects the substrate pH. Water that has low alkalinity, like RO water or rainwater, has little, if any ability to counteract the effects of a fertilizer containing high levels of acidic nitrogen. The RO Special that was designed for use with pure-water sources contains only five percent of its nitrogen in the acidic form. In comparison, the Well Water Special is designed for water with between 150 and 200 ppm alkalinity and has a higher amount of its nitrogen (30 percent) in the acidic form to balance with that type of water.



-- Bill Argo, PhD, received his PhD in horticulture from Michigan State University. He currently works for the Blackmore Company helping greenhouse, growers with their pH and nutrition problems. 10800 Blackmore Avenue, Belleville: Michigan 48111 (email bargo@blackmoreco.com)  

--Last edited by jesse on 2008-07-26 21:29:03 --