Zinc Overload
Description
Zinc Overload is a condition which describes an African Violet that is getting too much zinc (Zn). While considered a micronutrient, zinc is essential to the growth and vitality of African Violets. It plays an important role in the function of photosynthesis, thus contributing to those processes which give African Violets their green leaves. However, too much zinc can cause problems. A moderate overload of zinc, for instance, will cause some variegated leaf varieties to turn entirely green. Zinc Overload may be due to fertilizing with a formula that contains more than the recommended percentage of zinc. It may also be due to overfertilizing in which case you will probably see additional symptoms.
Distinguishing Symptoms
If you have a variegated leaf variety that has turned entirely green, there is a good chance that your African Violet is suffering from Zinc Overload. However, the "greening" of variegated leaf varieties has also been known to occur from too much sun, an excess of boron or an excess of nitrogen. While you may be able to rule out the possibility of too much sun, the complexity of plant nutrition makes it difficult to definitively diagnose Zinc Overload. (Note: Due to the complex interaction between plant nutrients, it is often very difficult to pinpoint the precise element causing problems. 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.)
Treatment
After eliminating the possibility of too much sun, 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. Wait one week before fertilizing again.
For standard-sized African Violets (in 3-inch pots or larger), use a Violet Food that contains about 14 percent nitrogen (N). For Miniature Violets, you should use a fertilizer that contains about half that amount, i.e., about 7 percent nitrogen.
If this does not work, either reduce the amount of fertilizer that your African Violet gets or reduce the frequency of applications. For example, if you fertilize every time you water, try fertilizing every other time, instead. When treating variegated leaf varieties, keep in mind that some are more sensitive than others to the amount of boron they are getting.
If none of the above works, your African Violet may not be getting too much zinc, but too much boron or nitrogen. Moreover, if this is the case, then the source may not be your fertilizer, but your water supply. Assuming that you have no way of testing the boron and zinc content of your water, try using another source of water, such as non-distilled, bottled spring water.
Finally, if your variegated leaf variety remains entirely green, then the problem may be genetic. For whatever reason, your African Violet may have had a mutation. In some cases, the Violet may be an unstable variety. In others, environmental conditions may have caused the change. In either case, the change may be permanent, or it may come and go as the seasons change.
Prevention
Use a fertilizer that has been specially formulated for African Violets. 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.)
About every three months, drench the soil with lukewarm water. 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.
For more about fertilizers and their effect on African Violets, see "Caring for African Violets."
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