Asked March 29, 2023, 9:01 AM EDT
I was hoping you could help tell me the cause of the leaf-yellowing that I saw recently [photos below] on a set of container-grown 'Green Mountain' Boxwoods at a nursery. The yellow margins were very uniform compared to any variegated boxwood species I've seen, so I didn't think this was likely to be a new cultivar or mutation. I only saw the yellow margins on the new growth coming out in shoots at the top of the plant. Other new growth lower on the plant was a uniform light green, and I couldn't find any sign of tip-yellowing on older foliage.
When I looked this up online, every source I could find with a similar photo or description referenced Magnesium deficiency as the likely culprit, with a handful also raising the possibility of Phosphorus deficiency, or a combination of both caused by low soil pH. My question is, why would Mg deficiency show up like this in Boxwoods? When I was taught nutrient deficiency symptoms during college, Magnesium chlorosis was always described as starting with the older foliage because it was a mobile nutrient. In most examples I've seen in other species, the chlorosis was interveinal and left the leaf margins green initially.
There were some very reputable sources referencing the Mg deficiency, including the American Boxwood Society and other extension offices, however I couldn't find any academic papers or research. If this has been proven to be Mg, is there a reason the signs seem to present so oddly in boxwoods? Is the path of this nutrient different in boxwoods because they're evergreen, or because of something more unique to them? And why does it only show up on a portion of the new growth?
I'd love to hear your input or read any literature you have that would explain this and improve my plant pathology knowledge - this sighting had me very curious.
Warren County Ohio