contagious rot in Cattleya new growth

[Ray]

First a general comment: Diagnosing nutritional deficiencies is fraught with obstacles that make it VERY difficult to do accurately. A deficiency in one mineral can look like a deficiency in another. Likewise, an excess of one can look like a deficiency in another.

Now, to that water analysis.

Right off the top, there is plenty of calcium, so that suggests a deficiency in that is apparently not the issue at hand. As a comparison, my plants have been getting only about 30% of that level at every watering for the past 5 or 6 years, and I have not experienced any symptoms of deficiency.

I could be wrong (no doubt to Orchid Whisperer's delight), but I think the "general nitrogen" is the sum of all of the other N-related levels, so you need not double count them. Also, the bicarbonate is a measure of the alkalinity of the water, that is, its resistance to a change in pH, and is not counted in the TDS.

The sodium and chloride levels are the only things of real concern from my perspective. Personally, I'd consider getting an RO system.

[Oranagra]

Ray, this test is the content of my tap water, which i never use (for fear of too many minerals).
The deficiencies my plants have are a result of using rain water and air conditioner condensation water.

So the question was if that tap water is safe for the type of orchids I have, or am I better off using cleaner sources (RO/rain/AC) , and adding supplements.

Anyway, what you pointed out seems right, in that case I have only some 500 ppm in my tap water.

[Roberta]

Based on that, the water really is bad. The chloride is especially the bad actor. With that kind of analysis, you are correct in using your supply of pure water, Wow! With that much chloride I would even hesitate to suggest blending in 25% tap water to get minerals...

[u bada]

I always had a hard time with cattleyas potted. I have similar conditions as you, although I do grow outside on a balcony as well as on windowsills, which has it's own challenges... anyway, did much better after I ditched the soaking bit and just been spraying water on surface at higher frequency than soaking 1 a week or every 2 weeks. I think there is just too much room for water to be sitting at bottom of pot and letting bacteria develop. At repotting I always noticed rotten roots at bottom of pot. Otherwise I'd have to let pot completely dry out and then the emerging roots wouldn't get water. Challenges of growing indoors on windowsill the ambient humidity just is not like a greenhouse or tropics where RH can foster growth development, or that's my theory. (in my grow tanks just don't get those kinds of problems.)

I have also really bad city water, the boron levels are horrible to note just one terribly high thing. I switched to RO water just a year ago and things are significantly better. I have a feeling there may be something off about the AC water. Using fert of course would keep you clear of mineral deficiencies...

[Oranagra]

wow. I'm really lucky I didn't trust the TDS meter, and managed to get a hold of that data.

[Roberta]

I agree with Ray, the "show-stoppers" are the sodium and chloride and RO would be a good idea. With reverse osmosis, you would still end up with small amounts of minerals (it isn't 100%) that should be fine for the plants. (For drinking the stuff, the nitrate is pretty worrisome... if the sodium and chloride weren't there rending the water unusable for plants, you almost wouldn't have to fertilize...) Let me guess, tell me if I'm right... you're near the coast (seawater intrusion) and in an agricultural area (nitrogen from fertilizer and animals)?

[Ray]

Sorry, I had forgotten that you used pure water, not the tap water - and I would continue doing so, but definitely get a fertilizer that contains calcium and magnesium, or additives that provide it.

Even without knowing for certain what the problem truly is, I think that's a wise direction to take.

[Oranagra]

Roberta, your guess is right, this is well water about 1 km from the coast, and over the years it was over-harvested and got somewhat salty. and yes this area has both lots of agriculture, and some livestock. plus, some of the crops are watered with "second hand" water.

[Oranagra]

Hi all, one last question hopefully...
I'm trying to figure out which Calcium supplement i can get a hold of... since shipping fertilizer from the US is quite expensive, and i can't find anything good here in Israel.

i read that the 4 main options that have been suggested in papers are:
* Powdered Dolomitic lime.
i'm not sure where to find that.. should i just go out, collect some limestone rocks and crush them?
* Gypsum.
Are we talking of the white powder used for construction?
* Egg shells / Oyster shells.
i can do that.. but for some reason it seems to me less effective.
* Cal Mag bottled solution.
I think i can get a hold of that in Israel...

can you tell me if i'm right, what is easy to get, and how do i decide the dosage?
thanks a lot.

[Orchid Whisperer]

Gypsum (or Plaster of Paris) is a great option, and inexpensive. Dissolve about a teaspoon (5 cc) per 4 liters water. It dissolves slowly, let it stand overnight. You can also add a similar amount of Epsom salts for magnesium. Both also provide sulfur, another nutrient.

Use a cup (250 ml) of this solution per 4 liters of water that you are going to apply to the plants.

You should still flush occasionally with pure water to avoid any build up.