Calcium/Magnesium deficiency?

[Johndeaux22]

I have a couple of Cattleya hybrids that have recently lost new growths. Initially I thought it was fungal or bacterial infection, however after further investigation, I don’t believe this to be the case. I fertilize with nearly every watering with K-lite at 25PPM, in the summer this is 3-4 times a week, in the winter it is 2-3, everything is grown indoors under lights or on window sills. Water source is RO, that typically measures at 10-15ppm. I suspect calcium deficiency, as well as magnesium deficiency on some plants.

I’m not sure whether I need to supplement with cal/mag, or if it’s possible I need to flush with plain RO water a couple of times to get the plants in the mood to take up what is present in the fertilizer. All of the plants in question are grown in either plain medium grade Orchiata, or a mixture of LECA/coconut croutons/orchiata. A majority of my collection is having no trouble at all. The plants in question are in more than one growing area, so I don’t believe cultural conditions are necessarily to blame.

[Ray]

K-Lite is designed to give the proper levels of both calcium and magnesium, commensurate with the amount of nitrogen supplied.

If the issue is occurring with "a couple of" plants and not everything receiving the same regimen, I'd look for another source.

If they are faster growing hybrids, maybe this is simply a case of not feeding enough. Is your "25PPM" TDS or ppm N? If it's the latter, then feeding 4 times a week should be fine, if it's the former, you're severly underfeeding.

Watering with plain water would exacerbate the issue, not stimulate the plant into taking more nutrition up.

Might the potting media just be too old?

[Johndeaux22]

Originally Posted by Ray

K-Lite is designed to give the proper levels of both calcium and magnesium, commensurate with the amount of nitrogen supplied.

If the issue is occurring with "a couple of" plants and not everything receiving the same regimen, I'd look for another source.

If they are faster growing hybrids, maybe this is simply a case of not feeding enough. Is your "25PPM" TDS or ppm N? If it's the latter, then feeding 4 times a week should be fine, if it's the former, you're severly underfeeding.

Watering with plain water would exacerbate the issue, not stimulate the plant into taking more nutrition up.

Might the potting media just be too old?

Ray, I target 25PPM N and use a quite accurate balance scale, originally intended for reloading ammunition to weigh the fertilizer (about 11.27 grains = .73 grams K-lite/gallon FYI). The plants in question have been repotted within the last 6-8 months, so doubtful that this particular media is spent. One is Bc. Rustic Spots, the other is a complex Blc., both are still young plants, and growing at what I consider a fast rate - 3 new growths in the last year for the Rustic Spots, and 5 for the Blc.. After looking closer, both are potted in 100% Orchiata. Both are showing loads of root growth - went from 2” plastic pots to 4” terra cotta, and have filled the new pots with roots to the point that very little media falls off if tipped. They both, otherwise look like they’re doing well, definitely at a loss as to what could be wrong here.

[estación seca]

New Cattleya shoots blackening is usually lack of calcuium, which we doubt here, or insufficient watering. Especially in your climate Catt. seedlings pushing new growth shouldn't dry completely.

[Ray]

Orchiata, by itself, contains both calcium and magnesium, courtesy of the dolomite used in the curing process. Add the K-Lite to that and I seriously doubt any such deficiency.

[Leafmite]

If the new growths turn black and it isn't too much fertilizer, sunburn or freezing, it is likely calcium deficiency. It could also be the way they are potted. It is best to pot Cattleyas so that only the roots are in the media. This usually requires staking or wiring until the roots hold the orchid steady. My Cattleyas are potted in 1/4 inch lava rock and net pots or plastic pots with many holes so I never need to worry about bad medium. I water so that the water pours out of the bottom to flush the medium.

Cattleyas come from all sorts of places and some of those places deliver a steady source of Calcium...so, if a Cattleya has ancestors that grow in one of these places, they might need more Calcium than other Cattleyas.

I tried fertilizers with added Calcium and some of my Cattleyas were still unhappy...until I began to use my tap water which, I learned, has plenty of Calcium. I also add eggshells which, once they begin to decompose, offers a steady trickle.

This is a great place to look up the ancestry of orchids....

Home page of orchidroots.com

[Johndeaux22]

Ray, is it possible that light levels are excessive for the available nutrients? I have a dedicated space for (mostly) Cattleya tribe plants, and a few Australian Dendrobium that gets pretty well blasted with artificial lights for 8-14 hours a day, adjusted seasonally. This produces spectacular blooms, and above average growth rates, but I also know that I’m operating right on the edge of reasonable. I feed at the 25PPM N rate to accommodate some of my collection being in sphagnum, as well as a sprinkling of Pleurothallids that seem to like the low end of the TDS spectrum. Should I just start mixing at two different rates for the different plants in different growing areas?

I’m open to the idea of mixing some tap water with the RO to add a bit more calcium and magnesium to the mix, but also don’t want to overdo it. We run a softener for the household water, so I’d have to get it from one of the outdoor spigots. I’ve attached our most recent two well water test reports.

[Ray]

This will be a difficult diagnosis, especially considering that only two plants out of your entire collection is affected.

Adding your tap water won’t do much as it only has 1 ppm Ca.

Nutritional demand is directly related to growth rate, not light level, although higher light can lead to faster growth in plants that need it, so your concept of outstripping the nutrient supply might be a reasonable suspicion. This is the scenario I’m thinking:

The plants are fast growers, and your growing conditions favor it, so the plants are doing so. The externally-applied nutrient supply in insufficient, so the plant translocates them from elsewhere in the plant. The problem is that calcium, once incorporated into plant tissues, does not do so to a significant degree, so the new growths are starved for it and die.

You original post mentioned that you fed 3-4 times a week. In my book, that is the ragged lower edge - adequate for plants that aren’t particularly fast growers, but marginal for others.

For the first couple of years I lived here in NC, growing outdoors, rather than in a greenhouse, that level seemed “OK”. Now that I have drilled a little deeper into the needs for different potting media and watering schedule, they are growing better, but weren’t blooming like they had before, so I upped the concentration from 100 ppm N “weekly” to 150, and the turnaround was quite noticeable. I put quotes around “weekly” because that was more of a plan than a solid schedule, so I was probably feeding less on average, so boosting the concentration compensated for my busy schedule.

[Johndeaux22]

Thank you for the insight, Ray. I’m going to move forward with a heavier feeding regimen for a majority of the collection, and continue with the lower rate for the plants sensitive to higher TDS levels. I’ll report back in a couple of months. I examined most of the faster growing plants last night, and do see signs of magnesium deficiency (mostly yellowing between leaf veins etc. ), which one might draw the conclusion that Ca levels are also inadequate given the labeled content of K-lite. Assuming 3-4 applications/ week, is a 50PPM N target reasonable?

[Ray]

Originally Posted by Johndeaux22

Assuming 3-4 applications/ week, is a 50PPM N target reasonable?

Not out of the question at all.