I use expanded shale as a soil amendment for all North Texas Blackland clay soils and can attest to its ability to improve our tight, heavy soils. Expanded shale provides a permanent soil solution for aeration and drainage. Unlike compost and other organic amendments, expanded shale will not break down during the normal lifespan of your planted landscape.
Jack Sinclair of TXI Industries explains that the shale is mined and ground to 1" to l/2" range particles and then kiln fired. As it progresses through the kiln for 40 minutes at 2,000 degrees C, certain chemical processes take place in the silica content (60-70%) causing the material to expand. As the material cools, cavities are left after gases escape, leaving a porous lightweight chunk capable of absorbing water and releasing it slowly at a later time. Recommendations for using expanded shale come from Dr. Steve George of the Texas Cooperative Extension. He recommends expanded shale use in containerized pots and soil incorporation for improved water retention and proper drainage. Dr. George also remarked: "Based on a two-year research study and six years of field trials, I feel that expanded shale will open up and aerate heavy, sticky clay soils faster than any material that I have ever tested. Due to its porous nature, it provides aeration from within the shale particles and, in poorly aerated clay soils, resulted in a more extensive and healthier root system than did other treatments being tested. Even though I dearly love finished, plant-based compost, if I were limited to only one application of one soil amendment with which to open up heavy clay soils, I would take expanded shale and never look back!"
Expanded shale can be purchased by the bag or in bulk and is also blended with other organic soil conditioners for potting mixes and bedding mixes.