Expanded Shale

What Is Expanded Shale?

Expanded Shale is a lightweight aggregate that is an ideal growing media for hydroponic or aquaponic systems.  The shale is mined, crushed and fired under high temperatures in a rotary kiln, producing a clean, inert, porous, and light material.

Because of the large amount of cracks and fissures in the expanded shale, the media can retain a large amount of moisture which can reduce the amount of flooding cycles needed for flood & drain (ebb & flow) systems.  For aquaponic systems, there is a large amount of surface area per stone for producing beneficial bacteria for converting ammonia into nitrates.

Expanded shale has been used for nearly 100 years primarily as a building material. It is added to concrete to make lighter buildings and bridges since it is half the weight of standard crushed stone.  The aggregate is also used as an additive in clay soils to increase its drainage properties as well as a decorative mulch around buildings and gardens.

Product Comparison

There are several types of media that could be used in a hydroponic/aquaponic system. This table displays some of the pro's and con's for each option:


Bigelow Brook Farm ships product in bulk to authorized wholesale, distribution, and retail channels.  Bulk consists of the expanded shale packaged in 25 liter bags and palletized.  We also offer 40 and 25 liter boxes which are designed for standard UPS or FedEx shipping.  As a convenience and cost savings to our customers, we also provide the ability to drop-ship orders directly to the end-user.


To find a reseller, please visit our "Where To Buy" page.

For information on becoming a reseller, please contact us by filling out the form on the "Contact Us" page.


Should I wash the Expanded Shale before installing it in my system?

We recommend that you wash it first.  During the manufacturing process, the majority of the fines less than 1/2" (13mm) are removed.  There can still be some fines left in the media along with some residual dust.


What's the best way to wash Expanded Shale?

Many people will fill their grow beds with the Expanded Shale, disconnect the drain from the rest of the system, then flood & drain the grow bed once or twice.  In our test system, we just dump the Expanded Shale into a wheelbarrow, fill it with water, then shovel the shale directly into the grow beds.  We then dump the wheelbarrow through a 3/8" screen to catch the larger pieces and repeat the process.  For smaller amounts (to fill net pots), you can fill a 5 gallon bucket with shale and water and scoop the shale up with your hands or a trowel.


I have read that Expanded Shale is not pH neutral.  Is this true?

Expanded Shale is a silicon-based material that is pH neutral.  The heating process in the kiln creates calcium and magnesium oxides on the surface of the material which can generate an alkaline pH.  Simply washing the material prior to use will remove the oxidized dust.  A report by Texas A&M University Research and Extension Center pubished an article in "HortTechnology" in October 2002 about the chemical properties of Expanded Shale and the effects it would have on clay soils as an additive.  They state that "[Expanded Shale] will not measurably affect the pH of neutral or calcareous soils".


Can I plant seeds directly in Expanded Shale or do I always have to transplant seedlings into it?

Seeds can be planted directly in the Expanded Shale just like conventional soil.  Since the shale is more coarse than soil, we recommend when using small seeds, such as lettuce, to sprinkle them over the media, then wipe your hand over the shale to get them to fall between the stones.  Until the seeds germinate, it is best to raise the flood level or water frequently to keep the upper layer of the shale moist.  This picture is a lettuce seedling that has recently sprouted.


Where do I purchase Expanded Shale?

Our products can be purchased through one of our reseller partners.  They will provide a quality service to you by insuring you have all the necessary components for your growing needs.  We will then ship the product directly to you!  For a listing of some our partners, please click here.


I currently use expanded clay pellets (Hydroton). Can I mix Expanded Shale with it?

Hydroton and Expanded Shale can be mixed together without any issues. Expanded Shale can also be added to existing stone systems, which will help to increase the moisture retention in the grow bed.


How much does Expanded Shale weigh?  Will it float?

Depending on the moisture content, Expanded Shale weighs around 1.7 pounds per liter (0.77kg/liter) when dry.  Because of its porous nature, a very small percentage will float.  Eventually these pieces will become water-logged and sink.  There have not been any reported problems with grow beds "floating" when flooded since there are so few pieces that actually float.


What else is it used for?

Many people use Expanded Shale for growing orchids. Other people have told us that they used it as a biofilter in their outdoor water gardens or koi ponds.