I bought magnesium salts, mostly for my pepper plants actually. I was thinking of using it for my orchids, since some of them display yellow splotchiness and I've read that a magnesium supplement might help with that.

Now it says the content is 50% sulphur trioxide, and 25% magnesium oxide.

Dosage for regular plants is 35 grams per square meters, to just spread on top of the soil.

Anyone have any idea of what the amount should be of I dilute it in water and water my orchids with it?

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~ sebastian
~ blog

For orchids, it's the magnesium in Epsom Salts that's the more important ingredient.

If you accept that the amount used in the MSU RO formula, when used at their recommended rate, provides an acceptable amount of Mg, then we can match that at 3/4-1 tsp/gal, applied once a month.

[url="http://firstrays.com/free-information/feeding-and-watering/fertilizer-information/magnesium-supplementation/"]Read this[/url]

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Ray Barkalow, Orchid Iconoclast
Using science & logic to improve orchid growing

From what I understand, the msu thing is 2% magnesium? The thing I bought is 25%. So I'd need one tenth of a teaspoon in a gallon of water once a month?

How many grams is that?

I guess I'll need to buy a sensitive scale for this...

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~ sebastian
~ blog

There is no need to match the content, or be that specific in the amount applied.

Epsom Salts is a great additive, in that it has no impact on pH. Plus, as both magnesium and sulfur are mobile within plant tissues, giving a larger dose periodically, rather than a continuous, small dose, is fine. But to that end, commercial Epsom Salt ranges from about 0.64 to 0.8 g/cc, so a tablespoon per gallon is about 3g/L.

If it makes you feel better, I have given my plants as much as two tablespoons per gallon with no negative impact, before I started using a fertilizer that already contained a sufficient amount of those elements.

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Ray Barkalow, Orchid Iconoclast
Using science & logic to improve orchid growing

Thank you so much! This gives me a much better idea of the amounts. Hopefully the plants will appreciate it by flowering more often and getting more evenly green foliage

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~ sebastian
~ blog