Nitrogen Overload is a condition which describes an African Violet that is getting too much nitrogen (N). Nitrogen is an essential element for the growth and vitality of African Violets. It is important for overall growth and the development of green leaves and stems. However, too much nitrogen can cause problems. A moderate overload of nitrogen, for instance, will cause some variegated leaf varieties to turn entirely green. A heavy overload of nitrogen may actually change the pH of the soil and, as a consequence, deprive your African Violet of available nitrogen and other nutrients. In addition to those symptoms listed below, the toxicity from Nitrogen Overload can cause stress to African Violets which will leave them susceptible to disease, especially when it coincides with underwatering. Nitrogen Overload may also inhibit the absorption of magnesium, thereby causing a deficiency in that element. Nitrogen Overload may be due to fertilizing with a formula that contains more than the recommended percentage of nitrogen. It may also be due to overfertilizing, in which case you will probably see additional 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 Nitrogen Overload. However, the "greening" of variegated leaf varieties has also been known to occur from too much sun, an excess of zinc or an excess of boron. 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 Nitrogen 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.)
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 nitrogen they are getting.
If none of the above works, your African Violet may not be getting too much nitrogen, but too much zinc or boron. 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 zinc and boron content of your water, try using another source of water, such as bottled water.
Finally, if you still see no change, 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.
To prevent Nitrogen Overload, use a fully-dissolving fertilizer that contains about 14 percent nitrogen. (For Miniature Violets, look for a fertilizer that contains about 7 percent nitrogen.) Apply as directed, and never overfertilize.
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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