Taking care of calibrachoas' and hanging petunias' chlorosis. *The Ohio State University Department of Horticulture and Crop Science It has become a routine by now. Look for the calibrachoas and the petunias in the greenhouse. Explain to the grower what the yellowing of the foliage means. And then, discuss possible solutions. I have seen far too many yellow calibrachoas during my greenhouse visits. Calibrachoas and petunias prefer acidic substrates. These two genera originated in South America in subtropical areas where soils are very acidic. Occasionally, I have seen some calibrachoas with symptom of iron deficiency at pH 6. What's a grower to do? Determine that the problem is really high pH. Iron deficiency (or micronutrient deficiency) can be caused by high pH or by absence of the nutrient in the mix due to, for example, a mistake in mix preparation. Correct high alkalinity water. High water alkalinity is common in well water. The most common way of neutralizing water alkalinity is the application of acid. The most effective of them is sulfuric acid. If you are already applying acid, you may have to check your injector. If the injector is working properly, you may have to increase the amount of acid you are applying to the water. Caution! Some crops -- like geraniums -- do not like low pH. Increasing the amount of acid in the irrigation water may cause problems for these high pH loving crops. Cultivar selection. Try, as much as possible, to select cultivars that are less susceptible to this problem. In our cultivar trials, we have noticed that there is quite a difference in response to soil pH among different cultivars of both petunias and calibrachoas. If you are growing cultivars this year that are showing the problem, write down the name of the cultivar and do not order cuttings of that cultivar next year. Substrate pH. You have to maintain the pH of the substrate below 6. If you prepare your own mix, reduce the amount of lime you are applying. If you buy your growing mix, contact your provider and ask whether it is possible to have a special mix with less lime. Fertilizer selection. Use fertilizers that are acidic to keep pH low. A 20-10-20 would be a good start. When temperatures are a little warmer, switching to a 20-20-20 or a 21-7-7 may work. In general, fertilizers with high levels of ammonium-nitrogen are acidic. Apply iron as a drench. The best is the application of an iron chelate. There are different types of iron chelate. The one that has been show to produce better results is iron-EDDHA. This compound contains 6% iron, is more stable at all pH ranges, more soluble and more available to the plants. It can be found in the market under the commercial names of Sequestrene 138, or Sprint 138 . After application, as a drench, leaves should be washed to avoid phytotoxicity. The effect of this product is short lived if the real problem - high pH - is not corrected. How about the customers? A grower asked me what happens with these plants when they are sold and are subject to the control of the customers. My answer was: It depends on the type of soil (whether high or low pH), and if they keep the plant in the same container where it was grown, on the water quality they have and on what type of fertilizer they use. Chances are that the consumer will have problems if the grower had problems. Should we still be selling these crops then? In my opinion, yes, if two precautions are taken by growers and retailers: 1) growers should select cultivars less prone to have this problem; and 2) retailers should inform/instruct customers on how to minimize the problem. And by the way, the ability of retailers to provide their customers with helpful information is one of the advantages that sets them apart and justifies higher prices. * Mentioning of products in this article does not mean endorsement, nor lack of mention to other products implies a criticism. Always conduct a small test before applying any product to your crop. |
