Friday’s quiz was a tough one. Bernadette and Lisa B. gave it a good shot, guessing that this might be a phosphorus deficiency. While they’re on the right track (it is a nutritional disorder), the mineral of interest is iron, and it’s a toxicity problem, not a deficiency.
Under wet conditions (the affected Clematis is in the part of our landscape with a perched water table – see the March 15 posting), iron is predominantly in the Fe+2 form (ferrous) rather than the Fe+3 form (ferric). The ferrous form is easily taken up by roots, and when leaves accumulate too much iron they turn reddish-brown. This diagnostic characteristic is called bronzing, and it’s different than the reddening caused by anthocyanin accumulation. (As an aside, nonagricultural landscapes rarely have phosphorus deficiencies and are more likely to contain excessive levels of phosphorus.)
Finally, all this talk of iron has reminded me of one of my favorite chemistry puzzles – see if you can figure out what this is:
Give up? It’s a ferrous wheel!
These two Clematis are the same cultivar growing in my landscape about 15 feet apart. Both are growing on a fence facing north. Compare the leaves of the two:
Normal, happy Clematis
Not-so-happy or -normal Clematis
What do you think is causing the leaf discoloration? Very large hint: this is not a biotic stressor. Another hint: you’ve seen this part of our landscape before…back in March. For full credit, identify both direct and indirect environmental stress (in other words,  what is directly causing the discoloration in the leaves, and what is allowing  to occur, thereby causing stress indirectly)?
Answers on Monday – have a happy 4th of July.!
There’s a new blog already generating a lot of discussion among wine aficionados. The not-so-subtly named “Biodynamics is a hoax” discusses all things related to Rudolph Steiner and his philosophies, including the pseudoscience of biodynamics.
There is a common misperception among some that university researchers are in the pocket of Big Ag (see June 11 and 13 posts). So here’s a link to an article in today’s Seattle Times about the benefits of organic farming from a study at Washington State University. The research was published in Nature (one of the most revered of the scientific journals).