Re: [AGA Member] Re: iron testers

["roger" <roger@spinn.net>]

On Mon, 23 Feb 2004 12:47:03 -0800, Rachel Sandage wrote

> Great post, Roger. Now, dosing iron daily just isn't going to happen 
> for me - feeding the fish daily is pushing it. So, what do you 
> recommend for a substrate-iron-enricher?

Thanks, Rachel.

I think Flourish Iron is the only iron fertilizer that needs to be dosed
daily.  The stronger chelates seem to work fine when dosed once or twice a week.

I don't have much experience with things that can be added to an existing
substrate to provide iron.  I have used bits of iron gluconate tablets (from
the grocery store) and found them very effective.  I quartered the tablets and
pushed them into the substrate below plants that seemed to need a dose.  A
little bit goes a long way.  It's a useful method if you have iron problems
that are limited to one or two plants.  It's also a useful way (ideally,
anyway) to diagnose iron deficiency.  

I've also seen some iron-bearing root tabs for sale.  I haven't used any and
won't endorse any, though all the ones I've seen should work fine.

If you want to build a substrate that provides all of the iron that your
plants need, then you need to use soil.  If you need to build a substrate that
provides part of the iron then you can use an earthy substrate material and
combine it with a little peat, potting soil and/or organic garden soil. 
Another method is to just wait.  Even gravel substrates seem to be pretty good
soils when they get to be a few years old.

I think all earthy substrate materials contain quite a bit of iron.  The
substrate iron can become available to plants when bacteria use all the oxygen
in the substrate.  Once the oxygen is gone the bacteria start using other
things from the soil in the place of oxygen; in the usual sequence they will
use nitrate as long as it's available, then manganese as long is it can be had
fast enough and then iron.  The bacteria create (respectively) nitrogen gas,
soluble manganese and soluble iron.  If iron isn't readily available then the
bacteria will work on sulfate and that can have objectionable results.

The idea is to provide an earthy substrate, lots of places for bacteria to
work, low oxygen (usually meaning little circulation) and a reactive organic
content.  When everything works right the substrate will provide all or a good
part of the plants' iron requirements -- at least enough to hold the plants
over between doses.

The problem for folks like me is to provide those conditions without creating
a substrate that makes a mess every time it's disturbed.


Roger Miller
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