FEATURESTORY
by Ray Barkalow
Magnesium Supplementation for Orchids
M
agnesium is a major building-block in
the formation of chlorophyll, and its role
in the functioning of plant enzymes to
produce carbohydrates, sugars and fats.
Knowing this it is easy to understand the importance
of regularly providing magnesium as part of an or-
chid feeding regime. Unfortunately, not all fertilizers
provide magnesium, so we may find a need to add it
via some sort of supplementation. Fortunately, that is
easy to do using inexpensive Epsom Salt purchased
from your local pharmacy.
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But of course, we need to consider just how
much to use, and how often to do so. First let’s look
at the chemistry. Epsom Salt is a magnesium sulfate
mineral – giving a double benefit, as sulfur is a plant
nutrient as well. (Its name incidentally, comes from
a bitter, saline spring at Epsom, Surrey, England,
where it was found to be useful as a bath salt and
laxative back in Shakespearean times.) The form
that can be purchased at the drug store is the sept
hydrate, MgSO4•7H2O. By mass, that means that
Epsom Salt is approximately 10% magnesium and
13% sulfur, with the balance being hydrogen and
oxygen.
Many will acknowledge that the original, so-
called “MSU” fertilizer – is a very good, complete
fertilizer formula. It contains 2% Mg in its dry form.
In order to achieve the commonly-recommended fer-
tilizer solution concentration of 125 ppm N, the label
tells us to use 3.55g of fertilizer to make up a gallon
of solution. That means, therefore, that the gallon
contains 3.55g x 2% = 0.071g Mg.
If the fertilizer you are using contains no magne-
sium, and we want to add that same 0.071gram per
gallon using Epsom Salt, we would need 0.071g ÷
0.10 = 0.71g of Epsom Salt per gallon of solution.
www.GardenandGreenhouse.net
May 2018