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I am trying to determine the optimal potassium to magnesium ratio. I found some information that differs radically from each other.

Many sources says that K:Mg ratio in mEq should be 0.2 to 0.35 (e.g. A&L Canada Laboratories) - if I'm not wrong K:Mg 1:1 in ppm will be around 0.30 in mEq.
Some sources (e.g. Canna) says that K:Mg ratio should always be kept above 2 and below 10 - it matches the recommendations of some labs to keep the K:Mg ratio at 4:1 (e.g. http://www.bigpumpkins.com/DiaryImages/2019/Lrg/300848.jpg).

But I also found many soil tests from Western Laboratories that suggest that the ideal ratio K:Mg is 1:2 (e.g. http://www.bigpumpkins.com/DiaryImages/2016/Lrg/267877.jpg) which is totally different from all above. Is this just a mistake (swap Mg with K), or do they really recommend having more Mg than K in soil?

11/6/2019 11:41:39 AM

North Of The Border

I agree with western laboratories. Around 2:1 is probably best.

2/7/2020 11:38:39 AM

Watlington, UK

More Mg than K...?!? I think that's an obvious error

3/1/2020 3:54:51 PM

I thought the same when I saw it for the first time but when I saw it more times I started to wonder if it really is a mistake.

The same K:Mg ratio (1:2) is in the "Soil Amendment Estimator" which was recommended here few times.

In my soil, I try to have twice as much potassium than magnesium, but it seems that some growers prefer more Mg than K.

3/2/2020 2:58:53 PM

Coventry Rhode Island USA

If we look at our base saturation % which is how to balance the soil it should be like ! Just as a example . Calcium base should be 50 to 80 %
Mag 10 to 30 % and k 2 to 7 % which suggest that mag should be 2 or more times k !

11/7/2020 4:27:55 PM