Question
I have a deep purple ivy geranium. It WAS beautiful, but since I transplanted it, the new growth leaves are pure white. I've tried fertilizer, sun, and shade and it's still coming out white. It's not a fungus, I know that after reading some of your advice. So now what do I do? I really, really like this plant and don't want to lose it. P.S. I live in Houston, Texas...in case that makes a difference. Anxiously awaiting your response! Thank you in advance.

Answer
As I sit here in my ice-cold-freezing-air-conditioned office, I check your Houston weather and I see your problem: It's 98 degrees F. Houston was blessed 20 days during the month of July where the temps were in the 90's.  That's no way to live.  Maybe if you're a Pineapple.  Not if you're an Ivy-leaved Geranium.

Ninety-eight degrees.  Do you know that this is only .6 degrees F from our body temperature?

I have been dealing with plant problems for more than a quarter of a century, and NEVER have I seen so much trouble caused by the temperature.  This is truly astonishing.  We on Long Island are in the American Horticultural Society's Heat Zone 4.  Houston is Heat Zone 9.  That's hotter than H&*#.

Let's just say this: Extreme heat bleaches the leaves of susceptible plants -- such as your Geranium.

First, understand that Ivy-leaved Geraniums are not heat tolerant.  Chloroplasts in almost any normal C-3 plant cannot make Chlorophyll when the thermometer reaches into the 90s.  This chemical, Chlorophyll, is not stable, and it needs to be regenerated almost all the time.  Without the work of the chloroplasts, there is no Chlorophyll.  That means the leaf will be white instead of green.

You need more than Chlorophyll for photosynthesis.  These are chemical reactions.  You need several enzymes for it to work, complex protein catalysts.  And as you may know, all enzymes have optimal temperatures.  As the temperature rises, the enzymes work better and better.  But once you reach that temperature, the enzymes become less and less effective, until they don't work at all.

But when you have a heat wave--and especially when you have a series of these over several weeks or months--you actually COOK these enzymes.  The technical term for this is 'denatured'. Heat begins destroying enzymes, and photosynthesis comes to a screeching halt.

There is one other weather related phenomenon that would cause this symptom: Extremely intense sunlight.

On a typical day, photosynthesis improves as the sun gets stronger and light grows more intense.  This just gets better and better, until you hit 10,000 lux, and then it becomes fairly constant.  Eventually, though, there is TOO MUCH light.  Assuming the weather is pleasant enough for the chloroplasts to make Chlorophyll, everything they produce is, alas, instantly bleached.  And the leaves turn white.

I know many people would see those words 'white' and 'leaves' and think, Uh oh, Fungus!  Mildew!  But it does not sound like this is what is going on to me.  If you have access to some old stock of Messenger, the Harpin protein product produced by the defunct Eden Bioscience, you will be able to turn the recovery response on much more quickly.

You don't want to air condition the plant; these green things are not too good with a/cs.  You want to interrupt this nasty heat wave.  Keep the plant watered (but let soil dry out); I would stop fertilizing and grow it out of direct sunlight until the weather has become a little more human.  Just don't over-water or over-fertilize, or you'll have a really big problem on your hands.

Meantime, if you have any further descriptions on this, I would be interested in hearing them.

L.I.G.