How to know if you should be using CalMag

[YetAnotherOrchidNut]

I have read that a non-trivial number of folks recommend using calmag treatments, or using epsom salts as part of their fertilizer regime. I cant figure out how I would know if I should, beyond that I don't see any calcium related ailments?

Amsterdam water had[1] an average calcium content of 41mg/l and a magnesium content of 8.27mg/l, and a ph of 8.11 which i usually ph adjust down to ~6. I use a reasonably good fertilizer, and my plants seem happy. Do I need to worry about this at all?

[1] Waterkwaliteit drinkwater Amsterdam | Waternet

Moderators: Feel free to move to the beginners area if you want. "Advanced" is subjective I guess. :-)

[rbarata]

Please post photos of your plant's leaves.

[estación seca]

Looking at the plant is always the best guide, but I would think those amounts are adequate if you lower the pH as you are.

[YetAnotherOrchidNut]

Originally Posted by rbarata

Please post photos of your plant's leaves.

I've got a lot of plants so not sure what to photograph. I don't see any typical signs of extreme calcium deficiency from what I have read, but I don't think I would recognize onset symptoms for instance. Also, I feel like this is something where I should be able to know without finding out I have a deficiency after the fact.

---------- Post added at 02:31 PM ---------- Previous post was at 02:28 PM ----------

Originally Posted by estación seca

Looking at the plant is always the best guide, but I would think those amounts are adequate if you lower the pH as you are.

Thanks. What numbers would have made you say otherwise? Is there a framework I can apply here to understand this? I understand the ph balancing will release calcium to the plant, but how much is enough? It sounds like I would need to supplement if I were to stop ph balancing. What would you recommend then?

[camille1585]

Are you seeing signs of deficiency (black leaf tips, often on Catts) or have some calcicolous types (ex: some paphs)?

41mg/L seems like more than enough. Consider someone using MSU in pure water, when feeding 50ppm N, you are supplying qbout 30ppm of Ca and 8ppm Mg. Your orchids get the 41ppm at every watering, regardless of whether or not you add fertilizer to your water.

Also, where did you read that lowering the pH will release calcium to the plant? Unless your pH is very high or very low, most minerals are sufficiently available. I would not worry about pH 8. In a soil based environment, calcium availability is actually highest in the pH 7-8.5 range...

[YetAnotherOrchidNut]

Originally Posted by camille1585

Are you seeing signs of deficiency (black leaf tips, often on Catts) or have some calcicolous types (ex: some paphs)?

41mg/L seems like more than enough. Consider someone using MSU in pure water, when feeding 50ppm N, you are supplying qbout 30ppm of Ca and 8ppm Mg. Your orchids get the 41ppm at every watering, regardless of whether or not you add fertilizer to your water.

Also, where did you read that lowering the pH will release calcium to the plant? Unless your pH is very high or very low, most minerals are sufficiently available. I would not worry about pH 8. In a soil based environment, calcium availability is actually highest in the pH 7-8.5 range...

I have some paphs (Pinocchio and Maude) and some phrags (babies, I forget which). I have not noticed black leaf tips on my Catts.

I had the impression that the acid would react with the calcium carbonate in the water and turn it into something the plant can more readily absorb. But I could easily be mistaken.

Does bark count as soil in this conversation? :-)

[Ray]

Originally Posted by camille1585

Unless your pH is very high or very low, most minerals are sufficiently available. I would not worry about pH 8. In a soil based environment, calcium availability is actually highest in the pH 7-8.5 range...

Exactly... People have been mislead for years by that "nutrient availability versus pH" chart. That applies to SOILS, and in fact, is only applicable to the particular soil they used, as soils are highly variable in their makeup.

Cation Exchange Capacity (CEC) is literally related to sites in the soil that attract and retain ions. Those sites are predominately the edges of clay particles and microscopic organic matter. As the soil pH changes, those sites' charges change, affecting how well they grab and hold the ions. Orchid media have essentially no ion exchange sites. (There are some, but it is orders of magnitude less that that of any soil.)

That would lead one to conclude (as I did many years ago) that the pH of the solutions we pour on our plants is important, but it turns out that - within limits - that's untrue, as well, as the microbes in the medium and the plants themselves control that.

I'm really getting to like microbes! Folks around here have had rust issues with their fig trees, yet I have had none, likely due to my regular use of probiotics.

[camille1585]

My chemistry knowledge is rather limited, but I thought that calcium was present in different forms in water, both soluble and insoluble, not not just insoluble CaCO3? Unfortunately the water analysis rarely gives this information.

I will shut up now.

[YetAnotherOrchidNut]

Originally Posted by Ray

Cation Exchange Capacity (CEC) is literally related to sites in the soil that attract and retain ions. Those sites are predominately the edges of clay particles and microscopic organic matter. As the soil pH changes, those sites' charges change, affecting how well they grab and hold the ions. Orchid media have essentially no ion exchange sites. (There are some, but it is orders of magnitude less that that of any soil.)

I use bark amended with leca, perlite, charcoal, tiny amounts of sphagnum in some cases, tiny amounts of peat sometimes, and these days sometimes vermiculite instead of sphagnum. (In more or less descending order.) I have read up on CEC before, but i will read more. Thanks.

---------- Post added at 05:37 PM ---------- Previous post was at 05:29 PM ----------

Originally Posted by camille1585

I will shut up now.

Please don't. I value your opinion and reading your post lead me to investigating more on my own and im not sure if I was right, or if it depends on the ph balancer used. Also I am inclined to think that where you live and where I live the water management policies and quality levels are likely similar if only because of the shared regulatory regime. The water in Amsterdam is not chlorinated, is yours?

[camille1585]

Originally Posted by YetAnotherOrchidNut

Please don't. I value your opinion and reading your post lead me to investigating more on my own and im not sure if I was right, or if it depends on the ph balancer used. Also I am inclined to think that where you live and where I live the water management policies and quality levels are likely similar if only because of the shared regulatory regime. The water in Amsterdam is not chlorinated, is yours?

I don't think mine is chlorinated either. My tap water is purer than yours, probably because I live on the south edge of the Veluwe with the poor, acidic, sandy soils. The pH is also high (8) but I usually leave it as it is, and occasionally adjust with citric acid.

I can't link to the pdf directly (it's a download) but if you go here (Waterkwaliteitsoverzichten | Waterbedrijf Vitens) and look up Wageningseberg, you'll see my water quality report. (Note, list is not in alphabetical order!) Following advice from Akerne, I use Rainmix fertilizer because my tap water is very pure.