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Calcium/Magnesium ratio

Posted by spaceman13 6b (My Page) on
Tue, Apr 5, 11 at 19:45

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

Follow-Up Postings:

RE: Calcium/Magnesium ratio

  • Posted by tapla z5b-6a mid-MI (My Page) on
    Tue, Apr 5, 11 at 20:47

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.


RE: Calcium/Magnesium ratio

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?


RE: Calcium/Magnesium ratio

  • Posted by tapla z5b-6a mid-MI (My Page) on
    Tue, Apr 5, 11 at 23:14

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.


RE: Calcium/Magnesium ratio

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.

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