Greensand is a product derived from deposits of sandstone. This sand is, as the name suggests, green in color, and it is used by gardeners as a soil amendment to fertilize and to break up thick, heavy soils. Many garden supply stores carry this product, and can also order it by request. Versions for both organic and conventional gardeners are available, with organic versions tending to be slightly more expensive due to increased care which needs to be taken during processing to keep the product free of adulterations which could be problematic for an organic garden.
Also known as glauconite, deposits of greensand can be found in several areas of the world. This sandstone is marine in origin, and forms in environments where the dissolved oxygen content is very low. Deposits tend to be very rich in fossils because they are comprised primarily of dead marine organisms. These organisms also contribute to the high levels of nutrients in greensand. In natural deposits, greensand is very friable and crumbly, which makes it easy to process into sand.
In gardens, this product is used as a potash fertilizer, meaning that it is high in potassium, with a nitrogen-phosphorus-potassium (N-P-K) ratio of 0-0-3. Greensand is also rich in iron oxides, silica, lime, magnesia, and other minerals. These minerals are beneficial for a wide range of plants which can grow healthier and stronger with the use of greensand soil amendments. In cases where soil needs to be fertilized and amended to loosen it up, greensand can be a good candidate for soil conditioning as well. People should be careful about using it indiscriminately as a soil conditioner, however, because it can throw the nutrient balance in the soil off; gardeners should confirm that the soil will benefit from the blend of nutrients in greensand before using this product.
This product is not just useful in the garden. It is also utilized as a water softening product, and can be seen in use in some water filters to condition and soften water. Manganese, iron, and other impurities can be removed with a greensand filter to make water taste cleaner, and to address issues which can arise when water is too hard. Hard water can cause soaps and detergents to behave strangely.
Some companies add nutrients to their greensand, and deposits in different regions can contain different nutrient balances. For this reason, it is a good idea to check the information on the packaging to see what's inside, instead of assuming that all products are created equal.