Molybdenum Deficiency is a condition which describes an African Violet that is not getting enough molybdenum (Mo). While considered a micronutrient, molybdenum is essential to the growth and vitality of African Violets. It plays an important role in the conversion of nitrogen into usable compounds and contributes to the production of chlorophyll which give the leaves of African Violets their deep, green color. The most common cause of Molybdenum Deficiency is either a lack of available molybdenum in the soil or a pH imbalance in the soil which is inhibiting the absorption of molybdenum and other nutrients.
If your African Violet exhibits these symptoms, there is a good chance that it is suffering from a Molybdenum Deficiency. Assuming the absence of other symptoms, it is almost certainly suffering from some form of nutrient imbalance. However, due to the complex interaction between plant nutrients, it is often very difficult to pinpoint the precise element causing problems. Often, an excess of one element will cause a deficiency in one or more other elements, and vice versa. Short of sending your plant to a laboratory for testing, you will probably have to be satisfied with simply knowing that your African Violet suffers a nutritional imbalance without knowing the exact elements involved. This said, do not be discouraged. The recommended treatment will remedy all nutritional problems.
Ideally, your first course of action would be to test the soil for a pH imbalance, making sure that the pH is between 5.8 and 6.2. While reasonably-priced pH testing kits are available at most garden centers, you can successfully treat your African Violet without one. In fact, for most people, the best course of action will simply be to assume that the plant is suffering from a general lack of nutrients and that a pH imbalance may or may not be the cause of it. With this in mind, here is what you should do.
First, repot your Violet with fresh potting soil. After separating the rootball from its container, shake as much of the old soil from the roots as you can without disturbing the roots too much. Repot the plant in a potting soil that is light, porous and guarantees a pH of 5.8 to 6.2.
Next, drench the soil with lukewarm water and let it drain. When doing this, add enough water until at least a cup (8 oz.) of water has drained from the pot. This will help leach out any of the substances that may have contributed to a pH imbalance. If these substances were the cause of the problem, they may still be present in the old soil that clung to your Violet's roots.
After you let any excess water drain from the pot, wait one week. During this time, do not use a fertilizer. The nutrients in the soil will be sufficient until you begin fertilizing again.
After one week, you may notice that your Violet has already begun to recover. If it has, it was most likely suffering from a pH imbalance in the soil. In either case, you can again start fertilizing. When selecting a fertilizer, be sure that it contains approximately equal amounts of the primary nutrients, nitrogen (N), phosphorus (P) and potassium (K). For standard-sized African Violets (in 3-inch pots or larger), an NPK of 14-12-14 is recommended. For Miniature Violets, you will need a fertilizer specifically formulated for miniature plants, such as Optimara Miniature Plant Food. In addition to being fully-dissolving, make sure that the nitrogen is not derived from urea, since urea will cause Root Burn on African Violets. Sources for each of the three primary elements can be found in the Guaranteed Analysis, located on the fertilizer label. (Note: Many of the micronutrients, though essential to the health of African Violets, are often not listed on the Guaranteed Analysis. If interested, reputable Violet Food producers will generally be happy to send you a complete analysis upon request.)
Important: If symptoms begin to return, you may have a problem with your water. Some common problems with water include too much chlorine in the water and soft water. If you suspect your water to be the problem, repeat the above steps and try using non-distilled, bottled spring water on your plants. If symptoms clear up, your water is almost certainly the problem. To be sure, you may want to have a sample of your water tested at a laboratory. If you do, have them check the levels of boron, zinc, molybdenum, potassium and chlorine. Aside from chlorinated and soft water, these are the most common elements which, if contained in excess in the water, can cause problems for African Violets.
Use a recommended Violet Food or fertilizer specifically formulated for African Violets. Your Violet Food should be fully-dissolving and contain approximately equal amounts of the primary nutrients, nitrogen (N), phosphorus (P) and potassium (K). Miniature Violets generally need a slightly higher proportion of phosphorus, such as that contained in a 7-9-5 formula. Also, your Violet Food should not contain urea nitrogen, since urea causes Root Burn on African Violets.
Use a potting soil that is light, porous and guarantees a pH of 5.8 to 6.2. For best results, your potting soil will consist of mostly block-harvested, sphagnum peat moss. Other ingredients may be included to increase the porosity and stabilize the pH.
At least twice a year, repot your African Violet, using fresh potting soil.
About every three months, leach the soil of any substances that may cause a pH imbalance. To do this, water from the top until about a cup (8 oz.) of water has drained from the pot. Allow any excess water to drain.
Finally, do not use soft water. Soft water increases the saline content in your potting soil. This will alter both the pH and the electrical conductivity of the soil, thereby affecting an African Violet's ability to absorb the nutrients it needs.
For more about fertilizers and their effect on African Violets, see "Caring for African Violets."
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