OFA Bulletin May/June 2012 : Page 3

May/June 2012 • N u m b e r 9 3 3 can drive the pH of the substrate up or down. Depending on substrate pH nutrients are more or less available for uptake by the plant, even when they are present in the soil solution. Most of us have experienced iron deficiency in a petunia crop due to high pH or iron manganese toxicity in geraniums when the pH is too low. Fertilizer selection is crucial, selecting the wrong fertilizer for your water type (alkalinity) can cause a problem even when it is adequately delivering nutrients. Diagnosing the Problem Once the symptoms and causes of the symptoms are understood we can get out a detective’s magnifying glass (and diagnostic tools) and do some detective work. There are a few simple steps to take that again use the process of elimination to narrow down the cause of the nutritional disorder at hand. The first and probably most value tool you should use is a pH and EC meter, properly calibrated of course (Figure 1). Knowing the pH and EC of your substrate will begin to tell you what path to start down. Are you seeing iron chlorosis and the pH is 6.8? Better start looking at why the pH is high. Do you have lower leaf yellowing due to nitrogen deficiency and the EC is 0.9 mS/cm? Why is the fertilizer not getting to and staying in the pot? Testing substrate pH and EC allows you to watch trends in the substrate. Substrate Testing Figure 2. The only way that you can look at the roots is to turn it upside-down and pull the pot off. Fertilizer Double check the recipe for your fertilizer and make sure that everyone in the greenhouse is mixing up stock solution using the correct recipe. The math involved in calculating fertilizer dilutions can be a bit overwhelming, which is why FERTCALC is available. Go to www.nhfloriculture.com to use the online fertilizer calculator to be confident you are mixing your fertilizer correctly (Figure 3). This is often overlooked but Figure 1. Checking the pH and EC of your substrate regularly will help avoid any nutrient problems. Inspect the Roots When was the last time you took a pot off of a plant and inspected the roots? Unhealthy roots cannot function properly. They maybe waterlogged, diseased, or absent for one reason or another. Getting into the practice of looking at roots on a regular basis can curb any problems before they get out of hand (Figure 2). OFA Bulletin Figure 3. Don’t ignore your injector. Be sure it is working properly so that it delivers fertilizer at the correct dose. Continued on page 4 3

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