Greensand is a greenish colored sandstone that is formed from ancient marine deposits. It is mined and then processed to a usable form to be used in garden applications. Greensand is comprised of green colored grains called Glauconite. Glauconite is found in nature as a rounded greenish tinted pellet like rock. It is made up of mica clay like minerals.
Greensand has been used for Centuries in garden applications. It has long been known as a soil conditioner, and for hundreds of years farmers have added it to their soil to create more productive fields. The exact chemical makeup was not known long ago, but the results they saw by adding greensand to their soil was noticeable. Thus, farmers added greensand to their fields generation after generation to keep productive food crops growing.
The average N-P-K for greensand is 0-0-3, but that can differ depending on where the greensand is harvested from. By looking at the n-p-k value you can tell that most farmers like to add greensand into their soil for the potassium content. Doing this with some fresh compost yearly, has kept many fields producing food year after year.
(greensand can come in many different shades)
Not only does greensand contain potash, but it also contains iron, silica, and can contain anywhere from 20 to 30 trace minerals. Again, the trace minerals will varying depending on which deposit the greensand was mined from. Iron is an essential nutrient needed for crops to grow, and greensand is an easy way to supply sufficient amounts to your plants. Silica helps to strengthen cell walls in plants, which in turn helps plants through times of drought, heat, and cold. With an ample supply of silica, greensand, can aid in you growing robust crops that can resist natures fury.
Another one of the long time known uses for greensand, was to increase the water holding capacity of your soil. Greensand can act like a natural sponge that can increase the water holding capacity of your soil so that you use less water on your crops. As clean water becomes more and more scarce, this will become more of an issue with future generations. It's amazing though that for hundreds of years, before chemical ag was a thing, farmers were using a natural product like greensand, to create soils that were more efficient when it comes to watering.
In parts of the world with less than stellar soils, adding greensand can help the tilth of soil in multiple ways. In clay soils, greensand can work to break up the compacted clay texture of the soil to make it more hospitable to growing plants. In loose sandy soils, greensand can help to hold the loose sand particles together to give the soil more structure. Since most soils are somewhere between full clay, and full sand, the addition of greensand can be a benefit to almost any soil.
The one thing I don't ever see people talking about with using greensand as fertilizer, is the time it takes to break down in the soil. The time it takes to break down and release nutrients that a plant can use is called bio-availability. Greensand can take 12 to 14 months to become bioavailable. Think about this when you see someone use greensand in their single use cannabis soil. Your cananbis plant will only be in a single use soil for a few months. This means the addition of greensand to your single use soil is a complete waste of time and money. When using in a field application, or with no-till soils, the application of greensand can make much more sense.
Using Greensand in Super Soil For Growing Marijuana
Since those early days of super soil recipes, greensand was an integral part of most mixes. Back then we used the soil once and then tossed it. Obviously we now know that with a bioavailability of 12 to 14 months, using greensand in a single use soil was a giant waste. In more recent times recycling your soil, or using your super soil in a no-till setup is generally the way people garden. Adding grensand to a recycled soil or no-till super soil can give the benefits of greensand after a few cycles. So in these super soil applications, it really does make sense to use greensand. Using the proper application rates is key to getting the most out of an application of greensand. Below you can use these application rates as a general guideline to start with using greensand as a fertilizer
Application Rates For Greensand Fertilizer
Vegetable Gardens & Flower Beds: 5lb-10lb per 100 square feet
Potted Plants: 1tbsp-2tbsp per gallon of soil
Trees & Shrubs: add 1lb to 2lb per hole with newly planted trees or shrubs
Field Applications: 500lb – 2000lb per acre of soil based off soil tests
Application Rate For Greensand In Super Soil Recipes
Per Cubic Foot of Soil: ¼ to ½ cup
Per Cubic Yard of Soil: 2.5lb- 5lb
Remember the use rates above are only a suggestion, and every situation is different. If you are ever in doubt, it always a best practice to do a soil test to make sure you don't throw the balance of your soil nutrients off.
When used properly, greensand can be an added benefit to many soils. As long as you consider the bioavailability period, and adjust your application rates based off of a proper soil test, your garden can see many benefits from the use of this age oil organic soil amendment.