Calcium Deficiency on Cattleyas - Orchid Board

amys · #1 10-24-2021, 06:45 PM

Hi, this is my first post here, although I've been a member for a couple years. I'm not exactly a beginner with orchids, but I'm far from an expert. Also, I wasn't sure which forum to post this question.

Can anyone help with this? Attached is a screenshot from St. Augustine Orchid Society, but this is my problem with 2 kinds of Cattleyas, while other types are doing well. SAOS says this is a calcium deficiency. This has been going on for a couple years, but I thought it was a fungus problem until I found the SAOS article. The fungicide seasonal regiment from Dr. Martin Motes' books that I follow has made no difference, and now I know why.
I live in SW Florida and have been regularly using Peter's 15-5-15 CalMag fertilizer for several years. The west coast of Florida has water that is highly alkaline, so Dr. Motes recommends this fertilizer. I use tap water and Hozon's Siphon Mixer and fertilize my orchids who are mostly on a covered deck approximately once a week in summer or every other week in winter. A couple of them are on trees with the same problem. Seems like my fertilizer should take care of this problem. They have fairly new potting medium. I've gotten advice elsewhere saying I'm using too much fertilizer, but if there's a deficiency, how can I be giving them too much? Any ideas?

SouthPark · #2 10-24-2021, 07:31 PM

It's hard to say what the actual situation is for now. For these orchids ------- relatively 'weak' fertiliser and relatively weak mag-cal application every once in a while will be fine. I just apply weak fertiliser and weak mag-cal once a month to my orchids. Other growers may have a different schedule ---- such as really weak for every watering.

My orchids have been doing great with just once-a-month.

Also - for your schedule ------ sometimes ---- once a week could possibly be too much, especially at 'regular' manufacturer-recommended concentrations.

The salts can just accumulate in the pot. And if the fertiliser concentration hanging around the media and roots region is too much, then I think it leads to some condition where water gets drawn away from the leaf tips ----- resulting in leaf tips getting not enough water ----- which negatively impacts the cells at the leaf tips.

Roberta · #3 10-24-2021, 07:32 PM

Do you have any measurement of the pH of the fertilizer solution? (Cheap meters are pretty inaccurate but give an idea, test paper is likely more accurate) I'm using RO for fertilizer now (with MSU cal mag) so pH isn't a problem and calcium is covered. When I was using tap water with fertilizer that was designed for that (fairly high phosphorus, which tends to acidify), pH stayed stubbornly at about 7.8 anyway... I brought it down to about 6.5 with vinegar. (Calcium bicarbonate is a powerful buffer, takes more than the small amount of fertilizer to neutralize the alkalinity.) I never worried about calcium, the tap water had plenty, black leaf tips especially on thin-leaved orchids were more likely to be salt burn from the hard water.

estación seca · #4 10-25-2021, 03:21 AM

Given where you live, this probably isn't your issue - but letting Catts get too dry when making new leads will also do this. Any chance these were skipped, or you had really hot dry weather at some point when they were forming new growths?

amys · #5 10-25-2021, 08:04 PM

Thanks, everyone, for your advice. I appreciate it! You've given me a lot to think about.

SouthPark · #6 10-25-2021, 08:28 PM

amys ----- I don't know if any studies have been done on it ------- but I'm predicting and expecting that if we put fertilizer into the media, and provided the orchid has enough roots to get the fertiliser, then regular watering could just keep moving the fertiliser around (which might still be hanging around in the pot). And orchids grow relatively slowly as compared with say banana plants and papaya and bamboo etc. So - as long as the orchid gets some elements into it every once in a while, then that should be ok. This is for regular potting methods ---- eg, bark, scoria etc. Not hydroponic type methods.

Leafmite · #7 10-26-2021, 02:49 AM

Did you have much rain this year? Rain will sometimes flush the Calcium completely from the medium. Calcium is used when cells are being built, during active growth, and doesn't move through the plant as many other nutrients do, so making certain the supply is steady is important.

I noticed when I went through Calcium deficiency that some Cattleyas were perfectly fine and unaffected while Black rot went through the rest of my collection like a wildfire. This led me to believe that some Cattleyas, based on their ancestry, probably need more Calcium than others (this is not verified, just an assumption I have made from observation). Some Cattleyas or Laelias (I cannot remember which) do come from environments that provide a steady source of Calcium so it would make sense if this is true.