Leaf Color Change In Humako Sweet and Neptune’s Jewels

Humako Sweet
Humako Sweet – Click to Enlarge Image

Back in July of this year, I had a number of Humako Sweet’s that I had grown from flower stem via tissue culture but they were not blooming and the dark green leaves were turning reddish. In some cases, the reddish color was giving away to almost a transparency of the leaf. See leaf A as compared to leaf B below.

Humako Sweet Leaves – Click to Enlarge Image

Plants were not wilting but growth appeared slow. There was no visible sign of a fungus or insect infestation or even its presence. My attention then turned to perhaps a virus infection. Was it the ” Impatiens necrotic spot virus” or for that matter one of the others that impact African violets? But the one odd thing that stood out was the leaf color change was only impacting two different plant varieties. The leaves of Humako Sweet as shown above and the leaves of my Neptune Jewels which are a lighter green leaf illustrated below. Leaf C is what all the leaves were changing to on the Neptune Jewels while Leaf D is the normal color.

Neptune’s Jewels Leaves – Click to Enlarge Image

What was happening? Do I submit leaves to viral analysis? All the other plants appeared fine, although I admit glowing slower than normal.

It just so happened that I attended a local Gesneriad meeting. There was a taped presentation from the National Gesneriad Society. About 3/4 through the presentation they showed a plant whose leaves were reddish and parts almost transparent while other leaves turned yellowish. The presenter noted that at first viral infestation was expected but that in reality, the true root cause was the temperature of the room it was growing in was very cool. At that moment it all came together!

I grow my plants in the basement of my house. It was July and it was hot outside and the air conditioning was running. The basement had the ductwork running through the ceiling of the basement and there were a number of vent openings that would cool the basement that was naturally on the cool side. I immediately purchased a thermometer and noted that the temperature in the evening would get down to between 16-18 degrees centigrade.

I closed the vents in the basement from the air conditioner, and within a few days temperature was in the 22-25 degree centigrade range and has been maintained in that range. All the red and yellow leaf color changes have stopped forming on the younger leaves (which are all green now) and remain green as the leaves mature. Only on the older leaves is the issue seen. But as the older leaves die off, evidence of the problem is disappearing. So I guess Humako Sweek and a Neptune Jewels are good indicator plants when the growing area is getting too cool. Their leaves turn colors like trees in autumn.

One Comment

  1. Kathy
    Posted December 3, 2019 at 5:57 pm | Permalink

    I see you’re keeping busy! 🙂

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