Saturday, January 3, 2015

RE-Mineralization 1



I recently encountered the new phenomenon (now a fad) of re-mineralization, while looking up some information (see That led to my purchasing Steve Solomon’s new book, The Intelligent Gardener: Growing Nutrient-Dense Food, which I am in the process of reading. The topic interested me because of my two gardening situations. I currently use raised beds filled with a soilless mix following Mel Bartholomew’s recipe: 1/3 peat moss, 1/3 vermiculite, 1/3 compost. Mel claims a scoop of compost is all you need to garden, but of course he insists that scoop of magical compost has to have all needed nutrients in it. Does it really? If it doesn’t that’s your failing, not his method. I have had mixed results with the soilless mix in my beds. Mechanically, it is great. It thaws early, drains well while retaining moisture, it has a light and fluffy texture that many plants love. But some plants (usually the heavy feeders) have not done well and that makes me wonder why. Are some essential nutrients missing? That is a complicated topic I have been thinking about for awhile and will be the subject of another post.


My beds are also located in a community garden where last year I had the opportunity to share half of an unclaimed plot for a garden. I used it for tomatoes, peppers and summer squash planted in-ground. The community garden was recently reclaimed from sodded fields whose history is vague to me. I doubt the field was ever tilled because of the large amount of ledge showing through in places. Maybe it was pasturage or hay field. At any rate, during the ice age it was under a mile thick layer of ice and the soil is some unknown mixture of silt, sand and gravel deposited by the glacier. So its fertility has always been in doubt in my mind, although fellow gardeners and myself have gotten decent crops from their gardens. I am curious to see how the soil tests out at and what could be done to improve yields for our gardeners using Solomon’s advice.


It all starts with a soil test.The photo above is a picture of a dried sample of the soil from the community garden that has been sent to Logan Labs in Ohio and to the UMass Extension service for testing. When dried, it crumbles easily and looks fairly sandy, but when we get our frequent heavy rains it compacts easily and becomes anaerobic. I have no idea of its actual soil type or composition. The worksheets Solomon uses assumes that the soil test used the Mehlich-3 extractant method, which is the method used by Logan Labs which he recommends. I also sent some of the same sample to the soil lab at UMass Extension, which uses a Modified Morgan method that includes micronutrients and is better suited to Northeast soils. The two tests will undoubtedly produce different numbers for nutrient concentrations and their target values will be different as well, so I am wondering how different the suggestions will be.


I called re-mineralization a fad because a lot of people have simplified it to just tossing a handful of rock dust around the garden. It has gotten so popular that many stores are encountering a large demand for rock dusts (I know, I just bought mine and got the last bag). Solomon's emphasis is much larger, however, trying to balance all the factors that make up the soil (pH, organic matter, minerals) so plants are given maximum opportunity to thrive and produce nutrient dense food. He talks about rebalancing the soil and that is the central theme of his book, not just mineralization. Using soil test results and the worksheets in the book, a prescription for supplements is developed to bring the soil into the right balance of pH, organic matter and ratios of minerals.


First step is to adjust the pH of the soil. The use of lime has been overemphasized in the past, and the recommended use of dolomitic lime can actually cause an excess of magnesium which tightens up the soil. Most vegetables prefer a slightly acidic soil, in the range 6.0 to 7.0. Solomon uses a target pH of 6.4. This target pH will actually be achieved when the four major cations (Ca, Mg, K, Na) are in the proper proportions. If you look again at the soil sample above, I am afraid that the white flecks you see are bits of lime from an over-eager distribution of lime early in the garden’s history. The last soil test in 2011 showed the soil to be alkaline with a pH of 7.6 with a very large Calcium content.


The next step is to address the amount of organic matter in the soil. Besides the usual mechanical improvement of the soil from adding organic matter and encouraging the growth of micro-organisms, the humus increases the ability of the soil to buffer not only cations (positively charged ions) but also anions (negative ions) so they are not leached away by rain and irrigation. There is no point in adding nutrients if the soil cannot retain them. The total ability of the soil to buffer/retain cations is called the Total Cation Exchange Capacity (TCEC) and is the key factor in rebalancing. Light (typically Southern) soils will have 2-4% organic matter and will have a TCEC less than 10. Heavier (typically Northern) soils will have 7-10% organic matter and a TCEC greater than 10. Solomon uses 7% organic matter as the target for northern acidic soils. He points out large additions of compost are not required once the soil reaches the desired level of organic matter and TCEC. The soil in the community garden in 2011 had a TCEC of 51.3 with 10.3% organic matter.


Next is balancing the major cations, Calcium (Ca), Magnesium (Mg), Potassium (K) and Sodium (Na). The target proportions are 68% of the ions buffered by TCEC should be Calcium ions, with 12%  Magnesium ions. Soils having this 68:12 ratio will be loose and friable soils. Higher amounts of Magnesium will cause soils to tighten and clump. Potassium should occupy 4% of TCEC capacity, with Sodium at 2%. If a soil has this 68:12:4:2 cation ratio, its pH should be at the target 6.4. It may take several years to reach target ratios if you have an excess of one mineral, so the prescription may be more involved than just adding supplements. The community garden test from 2011 (Morgan method) had a TCEC of 51.3, of which 98% was saturated with Ca, leaving only 1.5% Mg and 0.6 % K, definitely not a balanced soil.


Next is to balance the anions, the negatively charged ions. Any clay in the soil will only buffer cations. You need sufficient humus in the soil to buffer your anions or they will be easily leached away by rain or irrigation water. The trick is to build up and retain the anions to adequate levels, starting with Phosphorus. Phosphorus is an essential element and low levels of P will reduce plant growth long before symptoms of deficiency evident themselves. The goal for Phosphorus levels is P=K, a level equal to the Potassium content of the soil. Our old 2011 soil test showed a P level of 4 ppm compared to a K level of 108, a very low level of Phosphorus and far from the prescribed balance.


The other key anions are Sulfur, Boron and Nitrogen. Sulfur is an essential element used in building many amino acids. If elemental Sulfur is added to the soil, microorganism will readily convert it to the sulfate anion. In balanced soils, the goal is S= 1/3 P, or one third of Phosphorus levels. Higher levels of Sulfur equal to 1/2 Mg can leach cations from the soil, which can be an advantage if you have an excess of a cation such as Calcium or Magnesium. The sulfates of most cations are water soluble and will then be washed from the soil by rain. For Boron in light soils, Solomon recommends levels about 1 ppm and in heavy soils, 2 ppm. Nitrogen is heavily used by plants and easily leached from the soil so its amount varies so widely that the standard soil test does not test for it. Usually it is added when planting and as needed during crop growth and is not a permanent fixture of soil fertility.


So my soil tests for the community garden have been sent off and it will be a week or two before I get results. Then I will use the worksheets to calculate recommended supplements. The problem I have, which is probably beyond my capabilities, is dealing with the excess Ca and high pH of the soil. The Ca saturation percentage on the 2011 soil test was 98%, leaving little room for the other cations. Adding Sulfur would seem like a possible solution for both the Ca excess and the pH, but the soil already has a very high S content, equal to 2x Mg. I have no clue why that is. Hopefully, the new soil test will be more encouraging and these anomalies will disappear, maybe just the result of a bad sample in 2011.


  1. My soil had way too much sulfur and no copper when I first got here. And like you I had very little phosphorous and lots of potassium. I've always been a fan of rock dusts. At my last garden I used a lot of green sand as my soil was clay. Here I've used it but also azomite. Not for anything specific though, I just figured all soils are probably missing some micronutrient.

    BTW glacial rock dust is one that is used to remineralize, so your old glacial patch might be better than you think. Though those glaciers have been gone a long time so maybe not.

    1. I have used greensand in my raised beds because I had some and I figured the micro-nutrients in it would be helpful. This time I have picked up some local stuff, ,BrixBlend Basalt from the Pioneer Valley, which is also certified to be para-magnetic, if you're in to that. The soil in the community garden is actually not deficient in micronutrients (except no copper), so you're right about the glacial soil helping that.

  2. Very comprehensive post - I had heard briefly about this but didn't realize it was as complex as it is. There is always something new to learn!

    This spring I am planning on doing a comprehensive soil test on the new beds - they all contain the same triple mix & were amended more or less the same with greensand, compost, etc. At this stage, I am more worried about making sure that their pH is ok & that they are within range on most of the basic nutrients.

    My question would be how you deal with your beds at home. Since they don't contain soil, per se, how would you know if you are short on a particular nutrient? I look forward to your upcoming post on that topic.

    1. That's the problem, there really isn't a test specifically for this type of mixture and Mel argues you don't need one. A standard soil test is a waste of money because the results will be meaningless. UMass does offer a test for soilless greenhouse media, which is really designed to test the typical peat/perlite potting mixes. It does provide pH, conductivity, and nutrients (nitrate, ammonium, P, K, Ca, Mg, Zn, B, Mn, Cu, and Fe). You can add on a test for S and Na. That's probably what I will try using for my raised beds.

  3. I'm truly interested in seeing how your remineralization project goes. Frankly, I'm in the "toss some rock dust around the garden" camp, I figure it will help more than it will hurt. My interest turns more towards nurturing the microbiom in the soil, which is why I toss the rock dust or Azomite into the amendment mix, the mycorrhizae and beneficial bacteria supposedly thrive on the micronutrients and also make them more readily available to plants. I will also be experimenting more with cover crops and "green manures" to nurture the beneficial microbes in the soil. I think I'm getting positive results so far, but time will tell.

    1. I just bought a bag of basalt powder, a bag of kelp meal and a tub of crab shell to toss around my raised beds. I don't think you can be scientific about it. Supposedly produce grown with rock dust will taste better (subjctive) and have a higher Brix reading (measurable). You're right about the importance of the microbiome and Solomon's book is focused just on the soil chemistry. A good read is Jeff Lowenfels book, Teaming with Microbes and his second book, Teaming with Nutrients.

  4. I am way late on my reading (I was on vacation) but you did a great job of summarizing Solomon's approach. I got my soil test back from Logan labs and I plan on doing a post on my results (and my action plan) soon but I will share some numbers here for reference. My pH was 6.4, the TCEC is 11.5 and the organic matter is 4.2%, which is pretty good for my almost-southern garden. The major cations came in at 69:13:3:1, which isn't too far off the mark. but it's not all good news. My phosphorus is extremely low, and sulfur, boron, manganese, zinc and copper are low enough to affect the productivity of some of the veggies.

    I've now read Lowenfels Teaming with Nutrients, and I plan on reading his Teaming with Microbes ASAP to learn more about the microbial side of the whole jigsaw puzzle. It is safe to say I will need a multi-year effort to get our soil happy and healthy. I will look forward to your future posts on the subject too!

    1. I got the soil tests back and am working on another post. I have read further in the book and realize now we have what Solomon calls "fizzy" soil, basically over-limed. Since the Mehlich and Morgan tests use an acid-based extractant which dissolves the free lime in the soil, the Calcium amount is way overstated which distorts the TCEC and makes the numbers meaningless. I have used an adjustment to get a more realistic estimate of Calcium, and that will be the subject of the next post.


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