Where to begin? O.K., I have several Dendrobiums (most from section Dendrobium) that are showing similar symptoms. 1. The thin leafed types begin yellowing at the tips of the middle to older leafs. Eventually they start turning tan in color, dying back from the tips. 2. Those with a thicker leaf consistancy also begin yellowing at the tips or somewhere along the margin, but are much slower in actually dying and turning tan in color. Some do not begin dying off. They simply become chlorotic in spots. I have treated for both bacterial and fungal infections to no avail. I am beginning to suspect mico-nutrient deficiency or toxicity. Up here, we have water quality most of you would die for, very low in disolved minerals and other such things. Visiting guest speakers for the local O.S. have often recomended that we feed with every watering because out water is so clean and free of contaminants. I use a fertilizer mixture of: A crystaline 10-52-10 with a label assay of: N: 9.0% Ammoniacal 1.0% Nitrate P: P2O5 52% K: K2O 10% Boron: 0.02% Copper: 0.07% Iron: (Chelated) 0.15% Manganese: (Chelated) 0.05% The other fertilizer ingredient is a 0-10-10 fish _base_d fertilizer with a lable assay that includes: Chlorine: 8.0% (That strikes me as high.) I chose this material because I assume the marine fish _base_ should supply any and all micro-nutrients that might be needed. I fill a tub with 6 gallons of water and add the recommended amount of each fertilizer for 1 gallon. To my thinking this is the equivelant of adding a 10-62-20 requirement for 1 gal to 3 gallons of water, a 1/3rd solution. I fertilize at almost all waterings during spring, summer and fall, and few if any during winter. Potential causes as near as I can deduce are: DEFICIENCIES OF: Magnesium Cobalt Copper Iron Manganese Molybdenum Nitrogen Zinc EXCESSES OF: Calcium Chlorine(?) Potassium Phosphorus Zinc Can anyone comment or add any insight to this possible problem? Thx S V

        About the only nutrient deficiency that is going to manifest in orchids readily is iron; what you have doesn't sound like iron deficiency, and you're already putting iron on 'em. The second, much less likely deficiency that is seen in orchids is that of calcium, which (because it affects growing points first) isn't your problem.         I don't think you have a nutrient deficiency. I think you have salts build-up or, at least, that's the best I can guess without seeing the plants. Any pictures available?         If you have problems with root tips dying back, this would lend strongly towards this theory. More salt-sensitive plants (phrags in particular) that are in the same medium would be better indicators.         Some people have reported bad problems with salts buildup using coco fiber, even when thoroughly washed (and checked with a TDS meter afterwards); it seems to accumulate salts, at least here in the SW where our water is pretty nasty sometimes with regards to dissolved solids.         So- check your media, let us know if there are any mineral crusts. How are your root tips- dead or alive? Are more salt-sensitive plants showing any signs of stress? Do you ever use magnesium sulfate (Epsom salts) to exchange out some of the built up calcium carbonate? How much of the fish emulsion do you use? The 8% sodium is high, but expected given that it's probably from a marine environment, which already has lots of sodium present.         If all else fails and you don't want to believe me when I say I don't think it's a nutrient deficiency, then switch to a fertilizer that lists all your elements, right down the list:         Nitrogen, phosphorus, potassium         Iron, calcium, magnesium, manganese, zinc, boron         Cobalt, copper, molybdenum, and iodine.         Easy on the zinc. It's a little toxic if you use too much.         Still don't believe me? I'm cool like that. Get yourself a bag of Guaranteed* to Grow! or something like that from the local hydroponics store, some sort of micronutrient junk that is whipped up by some guy in his garage. It's a cheap way of getting your micros in a convenient form.         By the way- do you know what a molybdenum deficiency looks like in dendrobiums? Neither does anyone else. * Guarantee not good when used on plants, animals, or any other life form         No e-mail to the address in the header. It's a spam trap.         Cheers,         -AJHicks         Chandler, AZ

[Correction to my original post: water/fertilizer solution of 1/3rd strenght s/b 1/6th strength.] Thanks Aaron, Danny and Pat. Your feed-back has help put some things into perspective. I began using this fertilizer concoction early in 2000 after reading an article about windowsill growing in the Dec 1999 'Orchids'. The recommendation was to use a bloom booster year around. It has worked well for me with no apparent problems until this season. I began to suspect deficiencies or toxicity when the only info I could find for yellowing of middle to older leaves seemed to shotgun trace mineral shortages. Although, some potential excesses were listed. The reasons I began using this concoction were: 1. To use a bloom booster formulation year-round to help simplify my in-home growing of cool-dry-rest Den.'s that require a variety of tweaked conditions to make them all happy enough to bloom. 2. The crystalline fertilizer was chosen because of it's 100% useable Nitrogen content. Plus, some micro-nutrients were available from it. 3. Because I am always suspicious of manufactured chemicals which I assumed the crystalline fertilized was, I added the fish fertilizer to try to cover making other micro-nutrients available for just-in-case. I assumed the high Phosphorous would not be a problem. All I was trying to do was elevate the P-K above the N and make trace minerals available. This has worked well for me since early 2000. It has been only this growing season that the problem has begun to show severely on several plants. What I am now considering to be the indicator for this is a plant I purchased in 2000, a D. falconeri. The vendor didn't want to sell it to me at that time because he had had a bad water problem with them and they were still recovering from it. I brow-beat him into selling me one anyway. It has grown well for me until this season. It is now one of those plagued with yellowing and die-back from the tips of the older leaves. I am going to reassess my fertilizer regimen, lower the phosphoric acid content and not worry about micro-nutrients. In the meantime I'll do a thorough leaching of the pots and mounts to clear them out, then take another run at it. Thx for your input. S V

I am going to reassess my fertilizer regimen, lower the phosphoric acid content and not worry about micro-nutrients. In the meantime I'll do a thorough leaching of the pots and mounts to clear them out, then take another run at it. If you underfeed and use fish emulsion with an high Na content, you may have a sodium toxicity. Dendrobiums have proven to be able to replace a part of their potassium by sodium, during a potassium shortage... Basic : - Mix 1 part of substrate to 1 and an half part of water, by weight. Let stand overnight. Test the pH and EC. Optimum pH (according to foliar analysis, and comprising all possible deficiencies and toxicities of micronutrients) for SPENT medium is 5.7 for most hybrids of most common orchid genus... Optimupm extract EC  is over 400 and under 1000 ( depending on the genus). - Add some dolomitic limestone to raise the pH up to 6. - Use a 20-20-20 (best one is the 20-20-20 Florida Special from Peters/Scotts) at the microsiemens rates given above, pH 5.7, no more... - pH of the substrate will drop using this fertilizer. Check the water running out of the pot after a watering every other month. Too low, add lime. Too high, use epsom salts once. - Use from time to time a 15-5-15 CalMag or similar, but do not overdo it. Once every moth to once every other month is more than enough. Correct the pH to 5.7 too. - You may use calcium nitrate and magnesium sulfate monthly , but I have to know that those are more in excess than deficiency amonghst the several dozen foliar and substrate samples I am doing yearly. Magnesium sulfate - epsom salts - serves to supply SO4-, lacking in many culture, and lowering the pH, therefore making micronutrients available. Otherwise, the magnesium itself has no effet. IF you do not believe it, use magnesium nitrate instead... Good luck with your plants.