Brassia (Bratonia) yellowing leaves on new growth
 

Hi,
My Bratonia who in the past couple of years produced nice growth is not looking so good lately.
The leaves on the new growth started yellowing.

The only recent changes i can think of is that i moved it to semi-hidro about half a year ago, and that 3 months ago i started adding gypsum to my rain water since this forum helped me realize my Catts are suffering from Calcium deficiency.

I don't think these are the reasons, so maybe someone has a different theory?

thanks.

https://lh3.googleusercontent.com/E8...w1854-h1043-no

First, what are your growing conditions?

Second, why do you think your plants were/are deficient in calcium?

Third, gypsum is not very soluble, so it's not a good way to add calcium.

I grow all my orchids on my livingroom south facing windowsill (with window shades), I water with rain water and a random fertilizer weakly weekly.
I live in the north of Israel, and winter is quite cold.by my home is air conditioned (mainly on weekends)

in this thread it was suggested to me that my fertilizer is probably lucking Calcium, and since it is also absent from my (rain) water, my cattleyas new growths are blackening.

gypsum is what was suggested to me, I put half a teaspoon in 2L of water, and let is sit for a week before using it (half a cup per 4L).
i did notice it doesn't dessolve very good, but thought maybe the plants still manage to use some of it (since people argued that this is a good solution).

should I try to find a different way to add Cal?
do you think the gypsum is what causing this problem to the Brassia?

What are your temperatures day and night? How much light goes through the shades? Do you know the relative humidity near the plant?

I would look for a fertilizer containing calcium. With the gypsum you have no idea how much dissolves.

My temperature and humidity seem pretty constant.
About 20C (70F) - measured 18-21 in the last day.
and about 70% humidity (measured 63-76 in the last day).

The light I measure with my phone's sensor seems to be about 1000FC on average.
there are slits in the window blinds, and the direct sunlight part is getting to 4000FC, but the Oncidiums are located on the side that gets only ambient light, so about 1000FC.

So? Anyone knows what's wrong with that oncidium?
Could it be just late reaction to the semi-hidro setup?
Maybe it's just not getting enough water?

Are you watering often with just the gypsum water? I don't know how much of an impact it might have, but the pH of that might be quite high.

using rain water with some random fertilizer and gypsm.
Ph meter shows 6.9.
I use it every watering (once a week).

im coming to the US next month for a conference.
ordered both MSU formula, and K-Lite.

I'm not sure what's causing that. I have seen Oncidiums with leaves like that due to underwatering, sun damage and spider mite. But for all of these I would expect more of the plant to be affected.

Check for spider mites. There wouldn't likely be any left on the brown leaves. Take a tissue paper and press it against the underside at the base of each leaf. Run it up to the tip. If you see brown or red streaks you have spider mites.

The PH of 6.9 was from the Vanda bucket (which i replaced today), now it occurred to me that since it's in SH, i can test the actual waster, and i also remember seeing somewhere that Leca beads raise the PH. so i measure it and i see 7.3...

The underside of the leave has many brown spots.
but a wet cotton swap that i used to wipe some 3 leaves, came out with what mainly seems like dirt.

https://lh3.googleusercontent.com/4K...=w730-h1297-no

https://lh3.googleusercontent.com/kY...w=w699-h830-no