Am I giving too much Calcium to my orchids?
 

Hello everyone!

I have been trying to tweak the amount of fertilizer I give to my orchids but I was prompted with some questions about Calcium. I am using the RainMix fertilizer which follows the MSU formula but made available in Europe. The exact formula is 11,8N + 2,7P2O5 + 13,7K2O + 11,8CaO + 3,5MgO + 4,8SO3.

As you can see it has 11,8% of calcium. I water my orchids with tap water since it is really soft and I have been told in the past that it is not a problem but I checked the data of my water and it has 10 mg/l of Calcium which if I am correct is 10 ppm. I give my orchids about 100-125 ppm of N from the recommendations seen in the forum.

Now after seeing this and taking into account the amount of Calcium the RainMix fertilizer has (11,8%) I was wondering if you could tell me how many ppm of Calcium I am giving to my orchids since I am struggling to calculate it myself. I read that, without much testing done, it is recommended to give orchids about 40-80 ppm of Calcium and I am afraid of going overboard.

Thanks a lot for reading all this and I hope you can help me. I must say this forum (and the community in general) has been such a great source of information for my beginner brain and it has shown me how good of a community this one is in general full of great people so for that thank you again!

I suggest watching this YouTube video by Rick L. It's titled "Orchids......Magnesium and Calcium supplements". I am unable to attach a link.

Thanks a lot for the video. I just watched it and the conclusion I got it that he is not afraid of providing a good amount of Calcium with each watering so maybe my water solution with the fertilizer and my tap water is just enough for my orchids and isn't causing any harm

Alvaro - at 100-125 ppm N, Rain Mix is contributing 118-147 ppm Ca. The 10 ppm contributed by your water supply is of no consequence.

Rick Lockwood and I studied a lot of data before getting K-Lite formulated, which is a derivative of the MSU formula. It is 12.9%N and 10%Ca, so when I feed @ 100 ppm N, that includes 78 ppm Ca. In my last home, I used RO water, so that was it. My tap water here contains about 50 ppm Ca, so I'm dosing mine as much as you, and have been doing so for 8 years without issue.

The standard recommendation for plants in general is roughly 50-75 ppm Ca, but we must understand that with terrestrial crops and their extremely fine roots, the plant takes up essentially 100% of the solutions applied. 1L applied = 50-75 mg Ca absorbed. Because of the media used, if any, and their limited root system, orchids are unable to extract anywhere near 100% of what is applied, so our application of a "stronger" concentration translates to compensation for the diminished uptake.

Thanks a lot Ray. It's always a pleasure to get such good detailed responses from you! It's a relief to know I have been feeding them correctly.

It also makes total sense what you are saying about orchids not being able to take up most of the fertilizer we give them which is why I water like you recommend with every feeding and getting to those weekly 100-125 ppm instead of doing it once every 2 weeks for example. Right now to achieve that I use 0,5g per liter so I water twice a week and so far so good. I may experiment soon with using lava rock instead of bark for my Cattleyas so I may end up watering a bit more so I'll have to adjust a bit. Thanks once again!