Re: turn pink hydrangeas blue?

Title: Re: turn pink hydrangeas blue?
At 07:35 PM 10/9/01 -0700, you wrote:
>someone I was interviewing the other day told me that she finds that
>the iron phosphate snail bait she puts in her yard turns her pink
>hydrangeas blue.  Does that make sense?
>
>Nan

Nan:

I believe Moira is right.  Color in hydrangea flowers is closely related to
soil pH, kind of like living litmus paper.  Iron phosphate that is neutral
or basic is as insoluble as rock (Dufrenite is a basic ferric phosphate
found in limonite ore bodies - I'm not making the name up - this is from
Dana's Textbook of Mineralogy).  It would have to be on the acidic side to
affect slugs.

+++++---------------
        Iron salts, the chloride, the nitrate, the sulfate etc, exist in acidic solutions and will make neutral solutions into acidic solutions when they dissolve. They often will on standing deposit a brown fluffy rather gelatinous precipitate of the hydroxide. This when totally dehydrated becomes ferric oxide which we call rust!
        But plants need iron and if you put one of these salts on a plant and the soil is at all alkaline, the iron will simply precipitate and not be available.
        Aha, then comes the chelating agent. A chelating agent is one that puts the iron in a complex that stays soluble in alkaline solutions. But the trick is that the chelating agent does grab the iron, but holds it so loosely that it will give it up to the chemical systems in the plant after it has been absorbed into the plant tissue.
        We have a somewhat similar delicate balance in the blood. Hemoglobin which can be said to be a chelated iron latches onto oxygen as the blood passes through the oxygen rich lungs. Then it travels to the cells where they have been working hard, using oxygen and producing carbon dioxide. When the oxygen rich blood gets to the cell it is now in a carbon dioxide rich atmosphere and an exchange takes place and the hemoglobin releases the oxygen and latches onto the carbon dioxide. When it gets back to the lungs and the oxygen rich environment it dumps the carbon dioxide and takes up with oxygen again. It is very important that these "associations" be easily reversed. Carbon monoxide kills because it grabs onto the hemoglobin and won't let go and so the cells don't get any oxygen and they soon die!
        It's as though the parcels in a boxcar became glued in and couldn't be exchanged at the station for another load. The railroad would die, wouldn't it.

        You will probably agree with my wife that my analogies are at best a bit strange. But I hope you get the idea!                  ---Chas---
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