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Grow rhododendron (Alpine rose)

At first, please note that I'm an amteur about gardening
and I believe that gardening is a field with low reproducibility.
Then the following story may be an accidentally success.

One day, the energy of some rhododendron in my garden was lost.
At first, I doubt about the dryness of root by dry air of Japanese winter.
The department of an azalea have a shallow root and then there is no resistance in dryness.
Then I put some bark compost alound it.
And to down the pH, I put " Kanuma ground" that is popular soil for an azalea in Japan.
But I found some article says that some of recent " Kanuma ground" set to higher pH for general purpose.
I bought pH meter for soil and measure.
It is pH6.5, that is suit for many plants, but too high for an azalea.
I need to set down pH about 1 to 1.5, it is 10^1 to 10^1.5 times of hydrogen-ion density, that is deeply operation.
A pH adjuster changes an effect with buffer capacity.
And the base soil of my garden should be able to change easily.
An ammonium sulfate is popular to reduce pH in Japan,
though it have a time lag and there is possibility of the concentration obstacle of nitrogen.
Since sulfuric acid flows into water immediately, its term of validity is short.
Although there are materials for lowering pH of the ground which alkalized by mixing of the piece of concrete crush,
an phosphate may remain and these may produce inconvenience, when there is little calcium salt.
I'm looking for the materials to acidify, and found "Sandset" for blueberry soil.
The buleberry also require quite low pH.
I use this material.

If it hangs on mind and looks every day, what was not noticed until now can be seen.
It seems that the color of a leaf is yellow.
It investigated.
"If iron lack takes place, a leaf will become yellow, and only a vein part remains deep green " is written there.
It is right if it looks at.
Don't rhododendron need many iron rather than like acidity?
In other words, probably, a function will be weak, even if it does not have a means for absorbing iron from Fe3+.
The acid ground has the character which begins to melt ferrous oxide (FeO).
Fe2+ is obtained abundantly and a plant will tend to absorb iron, even if it does not have such a means.
Although it turned around the neighboring store,
the chelated iron in which manure is not mixed is not sold unexpectedly.
Since a concentration obstacle may be caused if a chemical fertilizer is added more,
some which have been mixed with manure have a sense of crisis.

I found the water-soluble chelated iron agent and use it.
The color of some leaves became good. Surely it is instantaneously effective.
However, more than fixed does not improve.
Then, since the granular chelated iron agent was found, it used.
Then, although the color of an old leaf is bad as usual, a new leaf has been extended steadily.
It seems that the peak was passed somehow.
It is fine after it.

The granular chelated iron agent is quite expensive in Japan.
Then I considered how to make by myself.
Since the following methods have not been tried yet, influence is unknown.

2 kg of citrate, 2kg of FeO, and 500g of the gypsum are well sprinkled on 20 kg of zeolite of agricultural materials.
It stirs, adding water with a watering pot (grade made to become wet).
It is put to sleep one whole day and night.
　 　

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