What Is Greensand Used For? (What It Does For Soil & Plants)


Maybe you have heard about greensand and how it can be used in the garden to improve your harvest.  However, that still leaves the question of when to use it, how to use it, and where it comes from.

So, what is greensand used for?  Greensand is used as a soil additive in gardening.  Greensand improves water retention of soil, since it holds 10 times more moisture than ordinary sand.  Greensand also improves soil texture by loosening up clay soil and binding sandy soil.  Greensand also contains potassium, which is an essential plant nutrient.

Of course, greensand alone is not a proper fertilizer, since it does not contain any nitrogen.  However, you can mix greensand into your soil along with other additives to get a complete and balanced nutrient mix.

In this article, we’ll talk about greensand and what it is used for.  We’ll also take a look at what greensand is and where it comes from.

Let’s get started.

What Is Greensand Used For?

Greensand is used in gardening as a soil additive.  It has many benefits when added to soil, since it contains nutrients and improves water retention and soil structure.

greensand in rock form
Greensand is used in gardening as a soil additive. It contains a good amount of potassium.

Greensand is versatile because it can improve two soil extremes.  It can bind sandy soil (which is naturally loose) or loosen clay soil (which is naturally dense).

Although greensand is not a complete fertilizer, it does have plenty of potassium.  Greensand is often used as a source of potassium in organic gardening.

Greensand releases its potassium slowly, over a period of several years.  So, if your plants need a quick boost of potassium, look elsewhere – the potassium in greensand will not be available to plants all at once.

Greensand also has other applications, including water purification.  It is often used as a filter media in water treatment systems.

The demand for greensand has risen, as a result of its increasing use in both organic gardening and water filtration systems.  The price of greensand has risen accordingly.

What Is Greensand Made Of?

According to the University of Maryland Extension, greensand is a naturally occurring substance.  To be more specific, it is a type of sandstone.

greensand in rock formation
Greensand is a naturally occuring type of sandstone.

Thanks to its micropores, greensand can absorb 10 times as much moisture as regular sand.  In fact, greensand can hold up to 1/3 of its weight in water!

Greensand is an iron-potassium silicate.  In simple terms, this means greensand is a type of sand that also contains iron and potassium.

Greensand also contains other elements (up to 30 others), but it is mainly composed of glauconite.  Glauconite is thought to form in small holes in the shells of sea creatures. 

Why is greensand green?  Well, glauconite is an olive-green colored mineral, which gives greensand its green color and name.

Greensand is slightly acidic, and it releases its water soluble potassium over a period of 4 to 5 years.  Greensand is coarse and often comes in larger pellets like sand (as opposed to fine particles like clay).

Greensand contains the following:

  • Marine Potash (Contains potassium in soluble form, which plants can use for growth.  Potassium is the “K” in NPK.)
  • Silica (Silicon Dioxide, which is found in soil and rock.)
  • Iron (An important trace mineral for plant growth.)
  • Magnesium (An important secondary mineral for plant growth.  A magnesium atom is the central atom in a chlorophyll molecule, which is vital for photosynthesis.)
  • Lime (Also called calcium carbonate.  Calcium is another important secondary mineral for plant growth.  It prevents blossom end rot in tomatoes and peppers.)
  • Up to 30 trace minerals (Small amounts of minerals other than those mentioned above.  These may include phosphoric acid, sulfuric acid, and aluminum).

Greensand NPK

The NPK (nitrogen, phosphorus, and potassium) content of a substance tells you whether it is a good fertilizer or not.  Generally, greensand contains no nitrogen (N) at all, and very little phosphorus (P).

greensand
Greensand contains no nitrogen, but has a little phosphorus and plenty of potassium.
Image courtesy of:
Brocken Inaglory via:
Wikimedia Commons: https://commons.wikimedia.org/wiki/File:
Green_sand_close_up.jpg

However, if greensand is rich in glauconite, it may contain up to 7% potassium by weight.  However, there is a lot of variability in the potassium content of commercial greensand products.

For example, this 0-1-6 greensand from Gardener’s Supply Company contains 6% potassium by weight.  On the other hand, this 0-0-0.2 greensand from Planet Natural contains only 0.2% potassium by weight.

Greensand is expensive, so if you are growing for profit, it might only be suitable for high-value crops.  In that case, you might want to consider buying in bulk to save money.

For example, you can buy a 50 pound bag of greensand from The Soil Makers.  If you really want to save, you can buy 40 or more 50 pound bags (1 tone or more) of greensand from Seven Springs Farms to get a discounted rate.

Greensand also contains small amounts of phosphorus, calcium, and trace elements.  However, if a soil test reveals a deficiency of any element other than potassium, you will need a soil amendment other than greensand.

What Does Greensand Do For Soil & Plants?

Greensand has several benefits for soil, including:

  • Water Retention (greensand will help dry soil to hold more water, due to its micropores and ability to absorb and hold water)
  • Loosen Heavy Soil (greensand will loosen up clay soil)
  • Bind Sandy Soil (greensand will give sandy soil better texture)

No matter what type of soil you have, greensand can help to improve its texture and water retention.  If you are growing in containers or raised beds that dry out quickly, this can really save your garden!

clay soil
Adding greensand to soil will help to loosen up heavy clay.

After all, when plant roots have access to water in moist soil, they are able to absorb more nutrients for growth.

The main benefits of greensand for plants are improved soil texture and water retention, rather than nutrition.  In fact, according to the University of California, greensand is best used as a soil conditioner rather than a fertilizer.

For example, in a field trial in New Jersey, potatoes grew better when the soil was treated with greensand.  However, this was likely due to better soil structure and improved water retention, rather than any benefit from added nutrients.

Although greensand does contain a significant amount of potassium, it is released slowly over several years.  It does not contain any nitrogen, and has very little phosphorus.

Thus, greensand by itself is not a balanced fertilizer.  It can help to improve your soil texture, and may release some potassium for plants over a long time period.

However, it is not a one-stop solution for a lack of nutrients in your garden soil.

How Much Greensand Do I Add To My Soil?

Down to Earth suggests applying 5 to 10 pounds of greensand per 100 square feet in a vegetable garden.

For a row that is 2 feet wide, this would mean using 1 to 2 pounds of greensand for every 10 feet of row.

Since the particles are so small, you can apply greensand with a spreader.  You can also mix it into the soil around individual plants by hand.

fertilizer spreader
You can use a fertilizer spreader to apply greensand, or mix it into the soil by hand.

The application rate for greensand will depend on your soil type.  If you are trying to loosen up very heavy and dense clay soil, then you might need to add a higher dose of greensand.

Using greensand for lawns may make sense if your soil is very dry (the grass is dying due to lack of water) or if the soil is heavy clay (poor texture).

Greensand Alternatives

If the cost of greensand puts it out of reach, don’t worry.  There are some alternatives to greensand, depending on your needs.

If you need to add potassium to your soil, you have a few alternatives to greensand:

  • Kelp – contains 4% to 13% potassium by weight, in addition to 1% nitrogen and 0.5% phosphorus.
  • Wood Ash – contains 3% to 7% potassium by weight, in addition to 5% phosphorus.
  • Compost – contains 1% to 2% potassium by weight, in addition to 1.5% to 3.5% nitrogen and 0.5% to 1% phosphorus.

You can learn more about these and other sources of potassium fertilizer in my article here.

wood ash
Wood ash can add nutrients to soil, including potassium.

Note that kelp and wood ash should be added to a compost pile, mixed in, and allowed to decompose.  This will make the nutrients available in a form that plants can use.

If you need to loosen up heavy clay soil, you have a couple of alternatives to greensand:

  • Gypsum – also known as calcium sulfate, this soil amendment provides two secondary nutrients that are important for plant growth.  Gypsum also improves soil structure by loosening clay soil without changing pH.
  • Compost – in addition to adding nutrients, compost will also loosen up heavy clay soil and improve its drainage.
compost bin
Compost is a good place to start to improve soil structure and add nutrients.

Conclusion

Now you know what greensand is used for and what it cannot do.  You also know where greensand comes from and how to use it.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

Recent Posts