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Epsom Salts

Posted by Nathan Parker 
Epsom Salts
April 29, 2021 01:30AM
Hello Everyone,
So I just got the highly anticipated soil test results back for the lot currently being converted from dense manzanita to apple and plum orchard and I've got an interesting finding that I would like some advice on. I have a significant magnesium deficiency (150lbs/acre) but am adequate in calcium (2050lbs/acre) and potassium (360lbs/acre). My pH is also in the sweet spot of 6.4. I have one opportunity to add soil amendment prior to turning the whole area into a no till ramial woodchip fungal heaven, and am considering adding Epsom salts to help raise the magnesium level without raising the pH or calcium with traditional liming (likely dolomitic lime). Has anyone done this on a large scale? My understanding is that Epsom Salts are pH neutral and is primarily magnesium sulfate. I do have a mild sulfur deficiency as well so this will help that problem also. I am hoping to get at least 150lbs/acre more of magnesium in the soil so my calculations are as follows: Epsom salts are 10% magnesium by weight so I would need approx 1500lbs of salts per 1 acre to increase the soil by 150lbs of magnesium. Any thoughts? Am I crazy?

Nathan Parker
Fiona's Apples
Zone 7b - Northern California
Re: Epsom Salts
May 12, 2021 09:56PM
This sounds expensive to me, Nathan. Prices here in the East for a 50# bag of Magnesium Sulfate are in the $26-28 range. I've worked with people who went about upping the base saturation ratio of Mg with dolomitic lime and then fertilizer rates of Sul-Po-Mag. (Those don't appear to be the right choices for you but then again you didn't share base saturation numbers.) One consulting client tried Epsom salts in back-to-back years, this as a surface application at a rate of 200# per acre but applied solely within a 6–8' radius of each tree. Soil testing the following spring revealed essentially little improvement in Mg with respect to cation balance. This does not rule out your idea and certainly someone can share area-wide numbers and perhaps prove those results to be a blip in time. The reality about soil numbers is such will always be a moving target despite the seeming exactness of chemical analysis.

My soils here want to see more magnesium as well. I'll be doing a second round of Sul-Po-Mag this summer (see the Summer 2000 newsletter to understand this timing). But mostly I include foliar magnesium as part of the holistic mix in Spring3, Comp1, and Comp3. This in turn gets sap results in the right place for Mg by midsummer. I've been using either a quart of Phyto-Mag (from Agri-Dynamics) or 5# Epsom salts per 100 when I do this. The Epsom foliar rate can be as much as 15# per acre if deemed necessary. I'm trusting the biology down below to be doing its part in this nutrient balancing as well. Over the long run, ramial wood chips and orchard compost are always going to help, if merely by raising the cation exchange capacity and thus the availability of Mg and other nutrients.

Lost Nation Orchard
Zone 4b in New Hampshire
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