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Expanded shale is a soil amendment that is gaining popularity among gardeners in the United States and for good reason. It can retain moisture, improve soil structure, deter ground-dwelling pests, and it never breaks down, unlike other organic additives.

What is Expanded Shale?

Expanded shale is sedimentary rock (shale) heated at high temperatures—often up to 2,000° Fahrenheit, which causes the shale to expand. The heat chemically alters the makeup of the rock resulting in a lighter, more porous structure. Expanded shale was traditionally used in building materials to lighten concrete structures. Only recently has its many uses in gardening applications been realized.

How Can Expanded Shale Be Used?

As a Soil Amendment for Garden Beds

Add about 3 inches of expanded shale on top of a new garden bed and till it to a depth of about 6 inches. For existing garden beds, work a 1-3" layer of expanded shale into the native soil at the same time as you apply compost in the early spring or fall.

In Potting Soils

Put a layer of expanded shale on the bottom of a potted arrangement to improve drainage and to mitigate root rot. Mix 1:1 expanded shale with a standard potting mix to lighten the potting mix for greater plant health and moisture retention.

As a Bonsai, Cactus, or Orchid Mix

Bonsai and many epiphytes like orchids require loose and airy growing mediums. Many aren’t even planted in soils; they’re planted in a mix of larger, chunkier aggregates. This loose structure allows delicate feeder roots to grow easily and rapidly, supporting overall plant health. Expanded shale can be used aesthetically on the top of planters, and can be mixed into the growing medium to allow for optimal oxygenation and moisture retention.

As a Barrier to Voles and Moles

Expanded shale can also be used as a humane vole and mole deterrent. Ground-dwelling pests do not like to dig through the gravelly texture of expanded shale. The shale particles effectively create a barrier for voles and moles when used 1:1 with native soils. You can even dig a trench around your garden beds filled with expanded shale to inhibit ground dwellers.

In Aquatic Applications

Expanded shale is a popular growing medium for hydroponics and water gardens. The porous material naturally filters the water, and it also creates oxygen pockets for the roots of the plants to grow and thrive. It does not break down in water and is a beautiful addition to a water garden or koi pond.

Discover the many uses of expanded shale at a nursery near you!

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