Growing African Violets, part 4 – Fertilizing

A good fertilizer for African violets is a well-balanced formulation of the “primary” elements of nitrogen (N), phosphorus (P), and potassium (K).  A 14-12-14 formulation is recommended for standard size violets planted in 3 inch or larger pots.  Miniatures or any violet in less than a 3 inch pot should be fed with a 7-9-5 formulation. 

 In addition to these primary elements, African violets need “secondary” elements in their feed.  There are 13 secondary elements essential to healthy African violets:  boron (B), calcium (Ca), carbon (C),  chlorine, (Cl), copper (Cu), hydrogen (H), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum(Mo), oxygen (O), sulfur (S), and zinc (Zn).    Carbon, hydrogen and oxygen are generally referred to as “free elements”, since the plant readily obtains them from water and air and they are rarely listed in plant food.  The other elements should be listed on the plant food label.   Some of them may be listed as “macronutrients” or those nutrients that plants need in larger quantities, such as N, P, K, Ca, C, Mg,  and S.  Others are “micronutrients” because the plant needs very small amounts for healthy growth. 

In addition to micronutrients, some fertilizers may list “trace elements”.  Trace elements are different than micronutrients, even though some people use the two terms interchangeably.  Trace elements are not critical to the life of the plant; micronutrients are.  There are four trace elements, in particular, that may be beneficial to your African violets.  Those are cobalt, (Co), nickel (Ni), silicon (Si), and sodium (Na). 

Even though some are macro and others are micronutrients, a proper balance of all is critical to the well-being of the plant.   In addition, it is important that everything you feed your African violet is fully water soluble.   All plants absorb nutrients through their roots and if the fertilizer elements are not fully dissolved in the water, the violets will not be able to absorb them.    This is especially true if you use self-watering planters or water only from the bottom.  Any fertilizer that is not fully water soluble will sit in your watering tray and not be available to the roots of your plants. 

 So, if you just buy a bottle or box of fertilizer labeled as “African Violet Food” you should be safe, right?  Not necessarily.  Urea is a common source of nitrogen in plant foods because it is cheap and readily available.  The problem with urea and African violets is that urea is known to cause root burn on violets.  Root burn prevents the violets from properly absorbing water and nutrients, eventually causing the death of the plants.

Guaranteed Analysis label of urea free fertilizer

 How do you know if your food contains urea nitrogen or some other type of nitrogen?  It should be listed on the “Guaranteed Analysis” label on your fertilizer container.  I checked the label on the most popular brand of liquid African violet fertilizer.  It contains 9.6% urea nitrogen.  Hmm.  Probably not the best for my African violets.  So, I was challenged to find a different fertilizer that obtained its nitrogen from another source, such as ammoniacal nitrogen or nitrate nitrogen, or a combination of these two.  I found it was not so easy to do.  I finally found a few options.  Peter’s Specialties produces a line of urea free fertilizers, as does Dyna-Gro.  The most readily available source of urea free fertilizer I found was the Optimara line, which sort of makes sense since Optimara is the most widely known breeder and producer of African violets. 

Once you’ve found the right fertilizer, how should it be used?   Neither under or over fertilizing are good for your plants.  Over-fertilizing will cause the leaves to become cracked and brittle and may produce lesions or “sores” on the stems.  Droopy or yellowing leaves, leaf tip burn, and reduced flowering are all signs of fertilizer overload.

To avoid these problems, always fertilize according to the label on your particular brand of fertilizer.  Different formulations require different dilutions or application procedures.    About every three months, you should completely drench the soil in your African violet pot and let it drain freely until the excess water is completely gone.  This will leach excess fertilizer salts away from the roots.  At the same time, wipe any visible salt build-up away from the rim of the container.

Who would have ever thought feeding your plants was so complicated?  Well, it really isn’t.  Just take time to look at the “Guaranteed Analysis” to see that it contains the critical macro and micronutrients, that it says it is “water soluble” and that urea is not listed as one of the sources of nitrogen.  The feed as directed on the label, leach your potting soil four times a year, and enjoy your healthy, productive African violet.

Tomorrow's news?  What to do when your health African violet outgrows its home.