Brassidium Yellow Star - Yellowing Leaves

Hello!

I’ve had this Brassidium Yellow Star ‘Golden Gambol’ for about a year and its been doing quite well up until a couple of weeks ago. I noticed that a couple of its leaves have started browning at the tips and eventually start turning yellow. One of these leaves is on the side of the pseudo bulb so no big deal, but the other yellowing leaves are on the tops of the two newest bulbs and I’m wondering what’s going on...

I have the plant in an east facing window with a couple other oncidium types and a few phals. It’s in a 4 in clay pot in bark (RePotMe’s All purpose orchid bark mix) on a humidity tray and it gets watered once a week. I water with RO water, but our RO system has a second set of filters that supposedly adds some minerals back in so it doesn’t taste so weird. I don’t know if that actually works, but the TDS reading is about 16 ppm. I don’t PH test but maybe I should? I fertilize when I remember about once or twice a month with MSU formula full strength.

I’m in upstate New York, so it gets a bit nippy this time of year. We keep our house on the cooler side in the winter, 68 day temps and 62 night temps. The plant is right up next the the window so it’s likely even cooler than the ambient room temps. Could the temps be the source of the leaf drop? What do you all think?

Any ideas are appreciated! Thanks!

A photo would be a great help.

What is "full strength" MSU, and which formula? When was it last repotted? Have you checked the condition of the root system?

I use 1oz/gal of the RO/Rainwater MSU formula.

It was repoted last February. Since it’s in clay I can’t see the roots well so I have not checked since I’d have to unpot it. I was waiting to hear if there were obvious temp requirements. The few aerial roots it has are plump (and really thick for an omcidium type! Weird.) and its psuedobulbs aren’t shriveled at all so I don’t think it’s dehydrated.

I assume that's the liquid stuff sold by Re***Me.com, so that tells me you applied 125 ppm N monthly. That's not likely to do any damage, and you're right, if the pseudobulbs are plump, roots are not likely the issue.

That "flavor enhancement" cartridge on your RO system is likely full of calcite, adding calcium, which is fine.

Yes, being too cold could definitely be an issue, and it might be exacerbated by evaporative cooling of the root system if your house has a low RH.

As a general comment, it would recommend that you feed 1/4 of that amount weekly, rather than doing so only monthly, and consider adding a teaspoon of Epsom Salts per gallon once a month.

Also, don't buy the liquid fertilizer in the future. It's very expensive, costs a lot to ship (you're paying for water), and as they are merely dissolving a pound of the powder per gallon of water, chances are that some of it drops out of solution over time, so you're not giving your plant the complete nutrition provided in the first place.

Our humidity is super low. I didn’t even consider that might be making it feel colder but it totally makes sense! I’m going to try moving a bunch of my plants on to a seedling heat mat and see if that helps any. Unfortunately, I’m probably not going to be able to convince the hubby to turn up the heat much. :) cost of oil and all that...

That’s an interesting thought on the liquid vs. powder fert. I’ll go for the granular stuff next time...it’s probably much easier to measure as well.

Thanks Ray!