Question
QUESTION: I recently purchased a couple orchids, both of which have been re-potted in wire baskets with glass pebbles as a potting medium.  My theory for this potting technique is that the wire basket would allow air flow to the roots, and light as well.  The transparent glass pebbles were chosen to allow the roots to photosynthesize.  In this medium, I water the orchids frequently (every other day) and the medium is dry within 6 hours since glass will not retain water.  Also the wire baskets drain completely in seconds. The roots appear to be doing quite well, they are green and plump.

I have two questions. The first relates to the underside of some of the leaves on one of my two plants.  The leaves look OK from the top side, but the underside is rutted with lots of little dents which are clustered closely together on one section of the leaf and this cluster appears to be growing in size.  It looks as though there is no inner flesh to the leaf where the cluster of dents are.  I see no insects anywhere.  What is this and how do I prevent it from spreading?

My second question regards the orchid food.  I use a 20-14-13 Nitrate Nitrogen based orchid food (no urea), but I dilute a very weak mixture of this when I water my orchid, since I water it so frequently.  The package suggests 1 teaspoon per gallon of water every 14 days, but I use 1/8 of a teaspoon per gallon.  Is this potentially a problem, and should I feed the plants less often?
Thanks for you help!

ANSWER: Douglas, additional information might be helpful.  Are you growing these orchids outside?  If not, where are you growing them?  If so, do the plants receive any sunlight?  I'm assuming that these are phalaenopsis orchids.  If not, I need to know what type of orchids these are. Also, you didn't mention how soon you noticed this after purchase.  It may be a pre-existing condition that went unnoticed.

I don't see a problem with your watering or feeding frequency or use of a dilute fertilizer. With the expanding condition on the underside of a leaf, there are a couple of possibilities that occur to me.  This may be mesophyll collapse which often is attributed to a sudden temperature change due to using cold water or overheating a part of the leaf due to focused sunlight. While this is not confined to the top surface of the leaves, it is often first observed there. A second possibility is the toxic build up in the leaf of certain components of plant food.  Since you haven't had these plants very long, I think we can rule this out. The third possibility, is a fungus infection which may have occurred prior to your purchase.

If you have other leaves on the plant, I recommend that you use a sterile razor blade and make a cut below the affected area.  That should prevent further spread of the condition.  Be sure to seal the wound with sulphur or a powdered fungicide. Also be sure to water early in the day when you do so.

---------- FOLLOW-UP ----------

QUESTION: Thanks Wayne, this is a phalaenopsis plant.  I purchased it 3 months ago when it was flowering.  At this point I have cut the spike.  These are indoor plants which have I think just the right amount of light, in a well lit room but 6 feet away from the window.

I am pretty sure that the condition with the underside of the leaves is something that occurred after I purchased the plant, although I do not know exactly when it started.  I can rule out any mesophyll collapse due to sudden temp change or cold water.  All water is at room temperature and there is no direct sunlight capable of overheating the leaves.  You mention that you have no problem with my frequency of water/feeding with a diluted strength fertilizer, however you also mention that toxic build up could be the problem in the leaves.  I have been watering my plant like this for approximately 1 month, sometimes every day, with the 25% strength solution.  If this is in fact toxicity from the plant food, is the damage reversible if I simply stop using the fertilizer as often?  
If this is fungus, I would hate to cut the leaves since that would leave too few healthy leaves on the plant.  All 4 of the effected leaves are the newest most robust leaves on the plant.  Thanks again for your advice and any further input is welcome.
Douglas


Answer
Douglas, it is unlikely toxicity-- which is a longer term problem.  Some experienced growers I know, use different plant foods-- rotating them to reduce chemical toxicity since each has a slightly different chemical makeup.  I doubt that you can do anything to reverse the damage that has been done.  Your best hope is to prevent the spread.  Mentioning that this is on the newest leaves does help some.  You could try two other approaches.  Purchase a Dynagrow product called ProteK to use in your watering/feeding.  This strengthens the leaf tissues.   Be sure you follow the directions carefully because if you use too great a combination, the leaves can become brittle.  In addition, you could try repeated fungicide applications to the affected areas.  I prefer a copper based fungicide such as Kocide.  If the problem is fungus related, this should limit the spread via sporulation.  Try this double whammy approach to see if it makes a difference.