Chlorosis in African Violets

A couple months ago, I noticed yellowing of the older, outer leaves of my African violet.  The leaves were plump, flexible, and had no signs of insect infestation.  That was a good sign.  The fact that the leaves were yellow instead of green was not - yellow leaves are not normal on an African violet.  I thought I knew what the problem might be, but I did some research to make sure I wasn't missing something.

African violet with chlorotic leaves

Yellowing of African violet leaves can be caused by a number of things.  A common cause of lower leaf yellowing is root rot.  In addition to the yellowing, root rot causes the leaves to droop and generally look unhealthy.  Eventually those leaves become mushy and brown.  Other than being the wrong color, my violet's leaves looked pretty healthy, so I was pretty sure I could rule out root rot.

Yellowing leaves can also result from too much light.  This usually causes the leaves to be smaller, look "crinkly" and feel leathery.  That wasn't the case with my violets.  This violet was furthest from the light source and violets closer to the window were not affected, so I didn't think it was too much light.

Yellow leaves can also be a result of too little light, however, this generally involves rangy, lanky growth of the whole plant.  My plant is low-growing and compact, so it is probably getting sufficient light.

There is a condition in African Violets which are cultivated under grow lights.called leaf bleaching. Lighter areas with a slight pinkish tone develop on the leaves directly exposed to the light. The only way to treat this condition is to stop using grow lights and begin using sunlight.  My violets grow in natural light in an east window, so leaf bleachng is ruled out.

That left me a nutrient problem to consider.  African violets need a good, well-balanced feeding regime to do their best.  They also need frequent re-potting, about twice a year.  I admit it - I didn't feed my indoor plants very faithfully over the summer months, so it's likely my violet is suffering from chlorosis.

Chlorosis presents itself as a pale discoloration of foliage. The leaf veins often retain their color while the rest of the foliage loses the green.  This usually results from a lack of nitrogen, potassium, sulfur and/or iron available to the plant. It can also result from a calcium deficiency, however, that is usually first noticeable in new growth, or the leaves in the crown of the plant.  Nutrient deficiency occurs because the plant isn't getting enough fertilizer, or enough light to conduct photosynthesis to use the available nutrients.   I'd already established that the lighting was ok, so the likely culprit seemed to be malnutrition - I was starving my African violet! 

My violet was probably hungry simply because I wasn't feeding it sufficiently, however, another common cause of chlorosis in African violets is "pH lock-up." This happens, when the pH of the soil is either too high or too low, and the plant isn't able to utilize the nutrients.   So, even though the mechanism is different, the plant is still starving.   Abnormalities of pH come from poor quality potting soil which starts off with too much or too little of one ingredient or another.  Another common cause is watering with softened water, which increases the fertilizer salts that collect in the soil.  I don't use softened water so that can be ruled out as a cause.  I am guilty of using a cheaper potting mix that I knew right from the start was not very good quality, so that, combined with my failure to feed, could be the culprits.

The only way to diagnose pH lock-up with any certainty is to pH test the soil and the water run-off  after fertilizing.  I didn't want to take time to do that and since I was pretty sure it had something to do with nutrients, it didn't really matter if it was from lack of fertilizing or if it was from pH lock-up.  The treatment was going to be the same.  I haven't re-potted my violets for about nine months, so it was clearly time to do that.

I carefully removed the violet from the pot and knocked as much of the old soil off the roots as I could without causing root damage.  Then I re-potted in fresh, quality potting mix specially formulated for African violets. 

I didn't divide the violet, as it hadn't grown much and I didn't want to stress it anymore than it already was., so it didn't need a different sized pot.  After allowing the roots to settle in for about a week, I began a fertilizer regime with a special formula for African violets that is urea free and balanced with equal amounts of N-P-K.   With weekly fertilizing, it is important to use ONLY the concentration of fertilizer recommended for weekly dosing.  It is tempting to use higher concentrations of fertilizers to make up for my previous neglect; this will put the plant into shock and potentially burn the foliage, possibly even killing the plant.

Once treatment for chlorosis caused by nutrient deficiency is started, the plant will be begin a fairly dramatic recovery.  Within just two weeks of replanting and one week of starting a good, healthy fertilizer regime, my plant is already beginning to "green-up".  While there is still a yellow tint to the oldest leaves, they are beginning to show more color and the center leaves are becoming a darker green.  And, I promise that next summer I will try very hard to be a better African violet owner...