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Phosphorus Deficiency


Phosphorus Deficiency is a condition which describes an African Violet that is not getting enough phosphorus (P), also known as phosphate or phosphoric acid. Phosphorus is an essential element for the growth and vitality of African Violets. Phosphorus aids in the production of healthy roots and plays a vital role in the production of flowers. The most common cause of Phosphorus Deficiency is either a lack of available phosphorus in the soil or a pH imbalance in the soil which can inhibit the absorption of phosphorus and other nutrients. Specifically, a Phosphorus Deficiency can occur when the pH is too low.

Distinguishing Symptoms

If an otherwise healthy African Violet has not flowered for a long period of time, it is very possible that the Violet is suffering from Phosphorus Deficiency. However, before you can make an accurate diagnosis of this, it is important to rule out the other possible causes for Violets that are not flowering.

First, check the roots. If your Violet has not formed a tight rootball, then it may be that your Violet's pot size is too large. This can cause African Violets to not flower. For different reasons, it may also be that your Violet's pot size is too small.

African Violets will also not flower when they are not getting enough sunlight. Make sure your Violet is getting plenty of indirect sunlight. The optimal light value for African Violets is 10,000-12,000 lux (about 900-1100 foot candles). Lacking a light meter, however, you can determine if your Violet is getting the correct amount of light by doing this simple test. During the period of day when your Violet is getting the most sunlight, hold your hand between the Violet and the light. If your Violet is getting the correct amount of sunlight, you should just barely see the shadow of your hand extended over the Violet.

Next, make sure the temperature around your Violet is adequate. Violets will not flower when the temperature is too cold. In order to flower, the temperature should be at least 68 degrees F.

Also, you should make sure that your African Violet is not suffering from Root Burn. If your fertilizer has urea nitrogen in it, Root Burn may be the problem.

Finally, make sure your Violet has not suffered from shock. Causes of shock include repotting, sudden changes in air or water temperature, and agitation, i.e., from dropping or shaking the Violet.

(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.)

Other Symptoms


If you suspect that your Violet is suffering from Phosphorus 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 Phosphorus Deficiency is to use a fertilizer with the proper percentage of phosphorus (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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