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Greensand - Why don't we have it?  Why don't you need it?

Greensand - Why don't we have it? Why don't you need it?

We get a lot of calls for Greensand this time of year.  Lately we've had to tell folks that we are out of stock, and unlikely to bring any back into stock.

So, is that a problem?  Not really. 

Greensand gained popularity in large part thanks to Eliot Coleman's books from the early days of Organic market gardening.  In The New Organic Grower, Coleman recommends the following for "Building the Soil":

  • Organic Matter - Compost or manure at 20 tons/acre, every other year.
  • Rock Phosphate - specifically "colloidal" or soft rock phosphate (though Coleman acknowledges that an equally compelling case can be made for "hard rock"), every four years.
  • Greensand (Glauconite) - "as a broad-spectrum source of micronutrients", every four years, or, dried seaweed which "breaks down more rapidly and has the additional benefit of stimulating biological activity in many soils".  Coleman later states that "if greensand is unavailable, a dried seaweed product like kelp meal will fill the same bill".  
  • Limestone - for calcium and magnesium, in sufficient quantity to keep the soil pH between 6.2 and 6.8.    
  • Specific Micronutrients - which should "usually be adequately supplied if the grower has paid attention to pH and organic matter", or as "gauged through careful soil testing".  Coleman notes that "boron is the one element most likely to need amending".

Readers of Coleman's books will know that he established his farm in Maine and that his soils required much building.  Reading into Coleman's recommendations reveals that he is working in soils very typical of New England.  From the currently published New England Vegetable Management Guide: "Micronutrient deficiencies are rarely observed in New England soils, especially on soils that have a history of compost or manure applications"..."Of all the micronutrients, boron (B) is most likely to be needed in New England to supplement soil levels for vegetable production."  The New England Vegetable Management Guide references a 1958 USDA publication as it's source, in addition to "information from Robert Becker, Cornell University." 

Over the last 30-plus years, small-scale organic vegetable production has radiated outward from the Northeastern US, and brought with it many ideas and practices.  Some of these legacy practices make sense in other parts of the country, and some do not.  Greensand may have a viable place in your soils, or it may not.  It's worth noting that the only source for high-quality, domestic Greensand was in the Northeast... more on this shortly.

Coleman's recommendations do not prescribe rates for Rock Phosphate or Greensand.  He is trusting the grower to make informed decisions, based on experience on their own farm.  He also describes making compost primarily from plant residues (which will have a notably different mineral composition than compost made from manures).  As we've discussed before, not all compost is created equal. 

The reality is, many soils do not need phosphorous amendments, especially where compost is applied.  We have learned since The New Organic Grower was written that vegetables do not remove phosphorous from the soil at a rate that keeps pace with the amounts put down in applications of manure-based composts.  In recent years, as many of our client's farms have gained time in production, we have seen more soil test results and fertilizer requests calling for nitrogen and potassium but no phosphorus.  Additionally, some states have put caps or time restrictions on phosphorous amendments due to environmental concerns.  

Coleman is advising growers to use readily available, regionally produced materials as amendments.  He describes making compost as "the most important job on the organic farm" and goes into detail about free or inexpensive, locally available ingredients.  This is why Eliot Coleman recommends Greensand or Kelp Meal - they were both relatively inexpensive (especially in the case of Greensand), readily available, regional commodities

There are many viable alternatives for a "broad-spectrum source of micronutrients", if and where they are needed.  Following along Coleman's line of thinking, the Newer Organic Grower should be looking for regionally-sourced, relatively inexpensive sources of trace micronutrients.  These would include things like:

  • Kelp Meal - from the North Atlantic.  The USDA Certified Organic Kelp we offer is a renewable resource and is harvested and processed by farmers, in an ecologically sustainable manner.
  • Alfalfa (Meal or Pellets) - from the North American interior, primarily the upper Midwest and Canada.  Our USDA Certified Organic Alfalfa is rich in nutrients.  When you use alfalfa you are supporting other farmers.
  • Montmorillonite Clay (also known as Azomite or Redmond Conditioner) - from surface deposits in Utah.  A classic broad-spectrum micronutrient source.

Applications of these trace nutrient sources are not specifically aimed at correcting measurable deficiencies, but rather "re-mineralizing" soils.  200 lbs/acre of any of the above alternatives should be plenty.  Because they are biologically-derived, Kelp and Alfalfa both work to help build and support beneficial soil biology as well.

As the Crop Adviser at Seven Springs I have reviewed soil tests from every corner of the country, every conceivable crop type and for every scale from 25 sq. ft. to 1000+ acres.  I have yet to recommend Greensand unless a grower expressly asks for it.  I recommend Kelp and Alfalfa Meals regularly.          

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So, why don't we have Greensand?  

The short answer is that the only domestic mine that produced quality Greensand has shut down.  This leaves only sources from Brazil or Russia.  Importing Greensand from Brazil or Russia eliminates it's two most redeeming qualities, as these materials are no longer regionally sourced, nor are they relatively inexpensive, to say nothing of the carbon footprint related to importing mined materials from half a world away.  We have tried imported Greensand with mixed results.  

The bottom line for us is that we would prefer to offer our growers the best materials possible while supporting North American farmers and companies like Azomite and Redmond by promoting better alternatives such as Kelp, Alfalfa and Montmorillonite.  These materials make better sense agronomically, biologically and environmentally... and I'm sure Eliot Coleman would agree.      

 

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Comments

Daniel - March 28, 2022

Mark – thanks for the questions.
Various materials have been marketed and sold as beneficial for “loosening clay soils” over the years, including greensand and gypsum. The potential mechanisms for this have been discussed and debated among farmers and advisers. What I can tell you is that we do not advertise these materials for this purpose (despite living and working with plenty of clay that could use a good loosening).
When a farmer asks me about greensand, gypsum and loosening heavy clay soils, my response is typically along the lines of “I’m not sure how that would work – but if you want to loosen clay soils I can confidently recommend getting your pH adjusted and then planting some deep-rooted cover crops with a goal of increasing organic matter”. There are lots of great cover crop options to explore.
As for greensand from Texas – I do not mean to disparage a domestic product. I have not seen the Texas greensand but would happily take a look at a sample and an analysis.
-Daniel

Stephen - March 28, 2022

Greatly, appreciate the updates!

Keith Lavern Curtis - March 28, 2022

Very good article. Thank you!

Mark Pipkin - March 28, 2022

Several sources say that greensand is beneficial for loosening clay soils such as what we have in Western NC. Can you comment on that topic?
Also to clarify are is the greensand from Texas source low quality?

Judi Gustafson - March 28, 2022

Thanks for the explanation.

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