How much calcium and magnesium?

[estación seca]

Like the title says. I have some MSU blend intended for mixing in rain or pure water, 13-3-15 with 8 Ca and 2 Mg. I bought this from First Ray's. Were the calcium and magnesium amounts likely chosen based on what the plants need, or what will remain soluble when mixed?

For my semi-hydroponic plants I use it at 1/8 teaspoon per gallon of rain / 0.17ml powder per liter, at almost every watering, which gives about 21ppm nitrogen.

My Vandas in vases get 1 teaspoon per gallon / 1.3ml powder per liter, at almost every watering, which gives about 170ppm nitrogen.

My other seedling plants of various genera get 1/4 tsp per gallon, about 40ppm nitrogen, and my adult plants of various genera get 1/2 tsp per gallon, about 80ppm nitrogen, at almost every watering.

Everything gets kelp in rain about once a month.

Are all my plants likely getting enough calcium and magnesium? Thanks.

[tucker85]

I think that's probably enough. If you have any issues with fungus, like leaf spotting fungus or new growths that turn black, then you could add a little more calcium to the mix.

[silken]

I am not very scientific about it. But I used MSU for tap and well water for a long time on my orchids. I had quite a few issues with black on growths. So I started adding a liquid Cal/Mag to my balanced fertilizer. It seems to have helped. My understanding is that MSU is formulated for all plants in general, not particularly orchids. So it may not be enough. Of course it would likely take a long time to find that out. I just add a couple tablespoons of the liquid Cal/Mag to my mix of 5 gallons of water with either MSU or Plant Prod balanced fertilizer. Something has changed for the better

[estación seca]

Calcium and magnesium phosphates can be extremely insoluble. There will probably be solubility issues if adding Ca and Mg to other fertilizer solutions. The Ca and Mg will likely precipitate out, though the concentrations are so low this would not be noticed with the eye. It is probably better not to mix the Ca-Mg with the fertilizer. That was why I asked my first question, about how the Ca and Mg numbers were chosen for the MSU blend.

[silken]

I don't know. It seems to really be helping my black spot issues so they must be getting it. And I am seeing a lot of first blooms too. Could just be coincidence on that but a few stubborn ones have decided to bloom for me since adding this about a year ago. I figure if it is added in regular fertilizer, a little more should be dissolvable too. But like I said, I am not basing my methods on any science at all.

[Ray]

The MSU "well water" formula was developed for use on orchids, when mixed with water supplies that provided sufficient calcium and magnesium. The "RO" formula was modified to provide calcium and magnesium when used with water supplies that did not contain them at sufficient levels.

The percentages were based upon two factors (trying to recall the conversations I've had with the developer): what is typical in water supplies, and in relative amounts to the other nutrients, as used by plants.

[silken]

I understood MSU was developed by Michigan State University (hence the name) and that it was supposed to be a fertilizer designed to have most everything that most plants would need. Not specifically an orchid fertilizer. I keep hearing that orchids quite often need more calcium than many plants, especially Cattleyas. I can see the R/O MSU being designed for greenhouse and hydroponics systems including orchids and therefor having more calcium, becauset most people won't be using R/O water on crops and gardens.

[tucker85]

Calcium, magnesium and sulfur are called secondary nutrients in agriculture. Secondary nutrients are used by plants in fairly large amounts but are available in almost all soils in sufficient quantities. For that reason they typically aren't included in many fertilizers. Secondary nutrients are also available in varying quantities in most water supplies. Of course, we don't grow orchids in soil so we lose one source of those three nutrients. Furthermore many orchid growers use rain water, RO water or tap-water that doesn't have enough of those three nutrients. All three of those nutrients play some role in plant resistance to fungus infections according to "Handbook of Plant Nutrition" by Barker and Pilbeam. I grow outdoors in Florida and black rot and leaf spotting fungus was a big problem during the rainy season. When I started adding a Cal/Mag supplement to my regular fertilizer there was a dramatic improvement. After four years of using Cal/Mag every time I fertilize, my orchids can sit out in the pouring rain for days on end and I seldom have any fungus issues. This year I experimented with sulfur also but after a year of using sulfur I didn't see any effect on my plants. Because of my experience I'm a big advocate of using calcium and magnesium on orchids, but I don't think they need extra sulfur. I've never had a problem mixing it with fertilizer water. The Cal/Mag that I use doesn't precipitate out. We all have different water supplies, different media mixes and use different fertilizers so it's important to experiment and see what works best for you. But for any grower experiencing fungus problems, I highly recommend using Cal/Mag.

[Ray]

Originally Posted by silken

I understood MSU was developed by Michigan State University (hence the name) and that it was supposed to be a fertilizer designed to have most everything that most plants would need. Not specifically an orchid fertilizer. .

No, it was developed specifically as an orchid fertilizer. It is labeled as "Orchid Special" in both formulas.

[silken]

Originally Posted by Ray

No, it was developed specifically as an orchid fertilizer. It is labeled as "Orchid Special" in both formulas.

https://www.aos.org/Default.aspx?id=417

This is one of the articles I was referring to. I'm sure I saw another one a few years ago on Michigan State Univ's web site but can't find it now. The 3rd paragraph indicates it was developed for a broad range of greenhouse crops, not particularly for orchids, although the author seems pretty thrilled with it on his/her orchids. The stuff we buy in bulk for our society does not say "Orchid Special" or anything about orchids. It may have enough calcium for some growers' conditions but I find a big improvement when adding extra calcium to the 2% present in the well/tap water formula of MSU. Maybe our tap water is low in calcium but I doubt it from the build up I get on taps and windows in the greenhouse that get some spray from the misters etc. There may have been some MSU formulas enhanced for orchids now that it is so popular.