Potassium Deficiency is a condition which describes an African Violet that is not getting enough potassium (K), also referred to as potash. Potassium is an essential element for the growth and vitality of African Violets. It plays an important role in many functions of the plant, including the accumulation and movement of plant carbohydrates. The most common cause of Potassium Deficiency is either a lack of available potassium in the soil or a pH imbalance in the soil which can inhibit the absorption of potassium and other nutrients. Potassium Deficiency may also be caused by an excess of calcium or magnesium.
If the leaves, including the veins of the leaves, have been yellowish for a prolonged period of time, and your African Violet exhibits no other unhealthy symptoms, then there is a strong likelihood that your Violet has a Potassium Deficiency. However, it should be noted that, even if you do see other symptoms, a Potassium Deficiency could be playing a part. The reason for this is that a Potassium Deficiency will greatly reduce your Violet's resistance to disease, making it more susceptible to viruses and other pathogens. If this is the case, the most important thing to do is to, first, address the other problems. (Note: 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.)
If you suspect that your Violet is suffering from Potassium Deficiency, the best treatment is to simply change fertilizers. If you are not using one, start now. A good fertilizer for African Violets will have approximately equal amounts of the primary elements, nitrogen (N), phosphorus (P) and potassium (K). For standard-sized Violets (in 3-inch pots or larger), the ideal NPK is 14-12-14. For Miniature Violets, look for a fertilizer that has somewhat lower percentages, such as Optimara Miniature Plant Food. This fertilizer is specifically formulated for Miniature Violets, with an NPK of 7-9-5.
The best way to prevent a Potassium Deficiency is to use a fertilizer with the proper percentage of potassium (see above, under Treatment). In addition, repot your African Violets at least twice a year.
For more about fertilizers and their effect on African Violets, see "Caring for African Violets."
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