Hi everyone from Auckland on this winters day.
I have been potting up some of my container citrus which i always grow in Terracotta but i have been growing in my new mix= standard potting mix/coarse pummice/magnesium fillings/gypsum and slow release fert with a NPK of 5/1/3 plus trace elements.
Today i removed an orange tree and potted up from a 31cm to a 37 cm pot...as you can see its a pretty impressive root ball and healthy green top growth...I also did a clementine a few weeks earlier and it was the same but i forgot to take a pic sorry.Both one years growth.
I have been having a lot of success with this mag/gypsum mix...vigorous growth,green foliage and abundant flowering and smooth fruits(better tasting too)...especially in ground but containers too.
It is towards the end of winter here and 90% of my trees are showing buds ready for spring(too my suprise as its still pretty cold)...Take a look
http://s1026.photobucket.com/albums/y326/laidbackdood/

Good for you! Your trees look amazing!

Your trees look very nice!

Have you thought about just using dolomite?

I am curious about how long the Mg shavings take to oxidize and become bioavailable.

Laidback, your growing talents have certainly improved. Your doing very well. - Millet

thanks for your kind comments....I am not sure how long the mg takes to dissolve but i think its slow.i ate a tangelo(pot) recently...first time i have let it fruit and it was full of juice and to my suprise=yummy....Didnt have high hopes for a young tree but i let it go really orange before i picked it.
I use gypsum as it supposed to loosen clay soil and improve drainage and its high in calcium and sulphur...It seems to be working for me along with the mg and gypsum is cheap too.My garden soil is a bit clay ridden.
Thanks millet...I have learnt a lot from the master i think.
Could you please give me your opinion on my comment here
http://citrus.forumup.org/about6707-0-asc-15-citrus.html
its the topic above mine on "forcing new growth"...i would be very interested in your thoughts...cheers Jon

laidbackdood,

you had better hope your trees don't get struck by lightning cause you're gonna burn the whole neighborhood down with a magnesium fire. And when the fire dept. shows up to throw water on your magnesium fire it will burn worse.

It seems odd that most anywhere that Mg shavings is sold it is an emergency fire-starter or fire bomb making or anarchist device.

Some states, the Mg has material safety data sheets attached to it.

Cool .i remember burning magnesium ribbon in school...that was pretty awesome.....I suppose it could be a danger in summertime but I only apply in spring and Autumn....Have just applied to my mandarin in the ground and all of my container trees about a month ago and they are going for it but i will bare in mind its flammable properties,thanks for that

Actually, metallic magnesium is not soluble, and therefore not available to the trees. I suppose the microbes could possibly break it down over time, but you will be long gone from this earth before that happens. - Millet (504-)

next time i repot,i will have a scan of the top soil to see if the MG is still there..The guy that sold it to me reckoned it slow released but i hear what you are saying Millet.Off the top of my head,I think i saw some when i did this last repot of my mandarin but all my container trees have it in now...so next pot up will show it.It is very fine shavings mind.Plus i do it spring and autumn but if it wasnt dissolving i would notice a big build up.
p.s just looked at my "orange in pot" thats on my photo bucket(visible on this thread) and you can see there is still Mg on the top of mix.....so maybe i will apply only once a year to my pots.Interesting.
All my pots are putting out spring growth right now.Looking good.
i fed that mandarin in the ground yesterday(the one that produced heaps last year)...i scuffed the soil up on the surface and didnt notice any mg there at all.So you maybe right Millet about the microbes.

Magnesium (metal) will slowly react with water to produce magnesium hydroxyde and hydrogen gaz (not in dangerous quantities).
No bacteria involved!

Mg + 2H2O --> Mg(OH)2 + H2

It might be a very good idea or at the opposite a very bad idea because magnesium hydroxyde provide soluble Mg AND hydroxyde that can raise the pH dramatically if the reaction speed is a little faster than expected.
If you have access to a pH meter, it would be a good idea to test your soil. I suppose there is nothing to worry about, because your tree look healthy, but a high pH can make your tree vulnerable to chlorosis.

Metallic Mg is not soluble at all, but with water it slowly become magnesium hydroxyde which is 100% soluble in your soil conditions.
So metallic magnesium is a slow release magnesium source with the side effect of raising the pH a little bit. (I can't tell if a higher pH is good or bad for a citrus tree, I know it make it more vulnerable to chlorosis but it might also control a few fungi/have unpredictable benefice. Most people grow citrus in neutral to slightly acidic soil.)
Magnesium sulfate (MgSO4nH2O) is also 100% soluble in a normal moist soil: that mean it can easily become accessible to the plant, but can as easily be washed out by subsequent watering. You must hope that there is clay or other cathion exchange material to keep Mg chelated (binded)and then available to the plant.

I hope I answered your question, I didn't use solubility table that are not usefull for a diluted solution.

Wow,thats very interesting...Of note is the fact that my soils in the ground are clay type....My containers are all putting out vigorous growth and seem very happy....I know it works well in ground but in container, is a new experiment...I will post pics in another months time.
Maybe,I should use acidic plant food then?