Using Greensand in an Organic Garden

Closeup of a pile of greensand

Aaron McCoy / Getty Images

When your organic garden needs to be enriched, you have several natural fertilizing options. One of those is greensand, an organic slow-release fertilizer that contains mineral deposits from the ocean floor.

There are many benefits to using greensand in your garden and lawn. It can enhance soil structure, increase root growth, and is good for the overall health of plants, because it gives them more nutrients.

Definition and Composition

Also called "glauconite," greensand is a material from the ocean floor that is mined to be used as a soil conditioner or fertilizer. It has a bluish-green color and is made of marine potash, silica, iron oxide, magnesia, lime, phosphoric acid, and about 30 other trace minerals.

What Is Potash?

Found in rock deposits, potash is a type of salt that contains large amounts of potassium, a nutrient that all plants need for both growth and reproduction. Because potash contains potassium in a water-soluble form, it makes for a popular ingredient in plant fertilizers.

While it sounds revolutionary, greensand is nothing new. It's been around for decades and is a popular tool that organic gardeners turn to often to fertilize their soil.

  • It is a good organic source of potash, which is important for overall plant health and disease resistance.
  • It is one of the best certified organic potassium sources and contains a high level of minerals, iron, silicates, and other trace elements.

Gardeners also find greensand useful when trying to improve hard clay soil. It will help texturize it and naturally boost the nutrient content. Sandy soils can also benefit from greensand because it increases soil's the moisture retention capacity. In fact, greensand can retain water and nutrients well, holding up to one-third its weight in water.


Most gardeners agree that greensand is a very beneficial natural fertilizer for a variety of reasons. They also enjoy that it's much safer to use than artificial fertilizers.

It is perfectly safe to touch greensand when working with it, and it is not toxic to humans or animals. If you have pets or children outside near your plants, you will not have to worry about exposing them to dangerous toxins.

Greensand will not harm all of the important microorganisms and worms in your garden soil, either. Since you have probably worked hard to create healthy soil, it's good to know that your efforts will not be wasted when you need to fertilize.


Greensand is not water-soluble, so it has to break up in the soil. Therefore, it is applied directly to the soil and not mixed in water. It is best when applied in early spring. The amount needed will depend on where and how you want to use it.

  • Trees: Use 1-2 pounds of greensand per inch of trunk diameter. Spread evenly over root zone.
  • Plants: Use 1-2 pounds per plant, depending on size. Mix into the top six inches of soil.
  • Broadcast application: Use between 50 and 100 pounds for every 1,000 feet of soil treated.
  • Lawns: The general recommendation is to apply 16 pounds per 1,000 square feet.
  • Flower and vegetable gardens: A good goal is 5-10 pounds per 100 square feet.
  • Bushes: Add 1/3 cup per bush when planting or fertilizing.
  • Potting mix: Mix in two tablespoons per gallon of potting mix for container gardens and houseplants.
  • Sensitive plants: Greensand can also be used on plants that are sensitive to other fertilizers and should not cause any damage. It doesn't burn plants like many fertilizers do.
Article Sources
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  1. Glauconite (Greensand). The Delaware Geological Survey