North American Fruit Explorers mailing list at ibiblio

["Donna &/or Kieran" <holycow@cookeville.com>]

Regarding dolomite and Mg, according to CEC notions, Dr. Albrecht and that 
lot, the ideal Ca to Mg ratio is 6 or 7 to 1.  However, it seems that God in 
his infinite wisdom did not make lime in that ratio, giving us a bit of a 
juggling act to do.  Dolomite runs 2:1 Ca:Mg.  All other limes run about 
10:1 or higher, we can even get a 33:1 from the Franklin mine near 
Nashville.  Ca and Mg do different things inside plants, and at very skewed 
ratios you can get deficiency symptoms, like blossom end rot in tomatoes 
when the soil pH is as high as you would want it to be.  Ca pushes soil 
particles apart, while Mg draws them together.  For this reason a tight clay 
soil will be improved by the higher 7:1 ratio, but will become much stickier 
if given only 2:1 dolomite.  We did this the first year, big mistake.  In 
the end we used the 33:1 lime to drive the pH just a trifle higher than I 
wanted it, but it brought the ratio back into line.  Sandy soils will do 
better with a 6:1 ratio to hold the particles a bit closer together.
   Another way to get some Ca into the soil is to use gypsum or calcium 
phosphate, which won't do much to the pH but will bring up the Ca without 
adding any Mg.  A local farmer near Carthage TN (source of our local 
dolomitic lime, so only dolomite had ever been used on his farm) found that 
his tomatoes did much better after the CaP, as much from the Ca he thinks as 
from the P.  I don't know any way to take out excess Mg after it's in. 
Plants will eventually use up some of it, so long as you don't keep adding 
more.  In Nova Scotia there may be mostly dolomitic lime, but it's possible 
that if there is some bigger city not too far away that some garden center 
may carry some bagged lime from further away.  That's what we have found 
here, that the nearest quarries sell it to farm supply stores loose to haul 
by the ton, but there are bags for your garden from places further away. 
Another choice, if you can find it, is any ground rock.  Mixed rock dust is 
supposed to be fantastic stuff.  The "glacial till" stuff.  Lots of minerals 
for your plants to choose from.  We can't get any such thing down here.  My 
son says that the really fine stuff, what Harvey Lisle calls rock dust or 
rock flour, is composed of such small and angular particles that it hangs 
onto water through simple mechanical attraction.  He claims their water 
holding capacity is greater than that of clay.  Maybe some of you folks with 
sandy or excessively well drained soils should try a test plot and let us 
know what you think.  He is also advising us to try the very fine granite 
dust from tombstones and countertops to seal our leaky pond.  He says the 
stuff is so heavy it will sink down into any holes.  He says he throws a 
handful into any potted plant that is letting water run through too quickly. 
This implies you could actually make trouble for yourself with it, but so 
far my practice of throwing it in planting holes doesn't seem to have 
drowned anything.  Of course, it hasn't rained normally in several years... 
As for the discussion some years back about some of the polishing materials 
being aluminum oxide, he says a bucketful of that will give off no more 
aluminum than a bucketful of clay.  He does say that in very acidic 
conditions there will be some dissolved, which does describe our soil, but 
then the soil would be a menace too, behooving us to add more lime!    Donna