Underside of leaves turning red

[wieb]

My dendrobium has a red blush on the underside of the otherwise healthy looking green leaves, but in odd patterns that remind me of a "farmer's tan" (well-tanned below the short sleeves, white above the sleeves).

The top of the leaves still look green with NO red.

Please see the pics.

dendrobium red & green underside.jpg
The underside of my dendrobium has tan lines!

dendrobium red & green underside2.jpg
Mottled, splotchy red blush.

It looks to me that the portions of the leaves that are reddish are the parts that are the most shaded, that may not get any direct light hitting them. I have light coming from multiple CFLs above and from the side, as well as a bit of light from an east-facing window (it has been quite cloudy in the Northwest lately).

Is this a problem/harmful? What causes this? What should I do about it?

I have seen references to this in other posts, but I can not seem to find them using the search function ... so sorry if this is redundant.

[brookn]

A bit of redness is not bad, and generally means that the light is optimal for growth. You can generally tell if a leaf is getting burnt. I would recomend not increasing the light too much more, and if the leaf starts to turn yellow or black, you might want to pull it back from the window a bit. Mine have a red tint to them, and are doing well, so happy growing!

[wieb]

It's a good thing then? Cool. I'll just keep watching then. Thanks again, Brookn.

[Cynthia, Prescott, AZ]

Any time you see strange looking marks or texture on the underside of leaves, you should look very carefully with a strong magnifying glass or jewelers loupe under very strong light just to make sure you don't have mites. Probably nothing in this case, but you need to be sure.

[wieb]

Cynthia,
I'll look at them closely with an eye loupe ... I need to start familiarizing myself with my orchids on this level ... I would be surprised, however, if any population of mites could leave such a clear cut line as the "tan line" seen on these leaves ... unless they somehow interacted with the light and shadow patterns.
Thanks.

[pikevi]

wieb: Yes, the 'tan-line' seems like a perfect semicircle (corresponds to the rim of the pot?) and that means it has got to be light.

I have one perfectly healthy ( or so it seems to my eyes) phal. which has the new leaf turning red at the lower side of the leaf. It is all over the leaf and has no clear demarcation as yours has.

[wieb]

The distinct demarcation lines are due to other leaves that appear to be blocking the CFL light. The portions of the leaves that get pretty much a direct "hit" from the light, whether it be from the topside of the leaves or the bottomside, have a nice green color on both sides of the leaves.

This may sound odd ("how does he get light on the bottomside of the leaves?") -- but the leaves stand pretty much straight up before curving toward the top -- and I have an old light pole with three sockets that rotate with a 23 watt CFL in each socket. (I also have an 85 watt CFL above in a clamp light fixture). Anyway, the lower light on the light pole actually illuminates from the side and therefore illuminates the bottomside of these leaves that stand up pretty straight. Some of the leaves, that are tucked well inside all the other leaves, have a completely red underside, no tan lines. It appears to me, shade = red undersides.

[wieb]

I'll rotate the pot so that the shade pattern changes. I'll try to get more light on these shaded areas and see what happens to the red coloring on the underside of the leaves. I'll report back later after a period of obervation.