Calcium/Magnesium ratio

13 years ago

I saw an article pertaining to "Global Buckets" Self Watering Containers that showed a photo of the analysis panel on a bag "Garden Lime" with the Calcium Carbonate (CaCO3) at 53.93% and Magnesium (MgCO3) 45.36%.

I checked mine to see what ratio mine had and found it to be CaCO3 82.5%, and MgCO3 at 8.36%.

I was thinking I was not providing enough Magnesium, so I did some research and found that a 10/1 ratio of Calcium to Magnesium was preferred...but the articles were based on LAWN GRASSES, not house plants, garden plants, vegetables and the like.

I recall reading that too much Calcium can can cause problems with Magnesium uptake.

SO...is the 10/1 ratio good for all plants, or is it just a lawn thing?

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Comments (4)

tapla (mid-Michigan, USDA z5b-6a)
13 years ago
Plants use roughly the same amounts of Ca and Mg, but the Mg fraction of dolomite is much more soluble than the Ca fraction. Generally ratios of 1.5-5:1, Ca:Mg are acceptable.

Al
spaceman13
Original Author
13 years ago
I'm assuming that reads 1 1/2 to 5 Ca to 1 Mg.
Therefore, my 10/1 ratio is lacking in Mg.

Should I consider replacing the lime? Also, I just ordered some DynaGro Foliage Pro 9-3-6, which states that it has 2% Ca and .5% Mg (4:1) Will this be adequate to make up the difference of my current 10 to 1, or should I just bite the $4 loss (LOL), and get a new bag of lime?

Thanks
Mark
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tapla (mid-Michigan, USDA z5b-6a)
13 years ago
I always figured that 4:1 was about ideal Ca:Mg ratio in containers. You shouldn't have any trouble if you're using the FP 9-3-6, if you incorporate 1/3-1/2 cup of lime per cu ft (about 8 gallons) of soil.

If you plan on growing tomatoes & get some BER on early fruits, don't be dismayed. With your plan, it's almost certainly an issue related to physiology and not soil chemistry.

Al
penfold2
13 years ago
There is one thing I don't understand. If the solubilities of CaCO3 and MgCO3 are what necessitate a skewed Ca:Mg ratio in dolomitic lime, then why do fertilizers like FP and MSU still provide a skewed ratio when using highly soluble forms of Ca and Mg? I would expect a 1:1 ratio in these fertilizers since solubility is not an issue.