All About Perlite

Appearing as tiny, roundish white specks amid the other components, perlite in potting soil is a non-organic additive used to aerate the media. Vermiculite is also a soil additive utilized for aeration (though less so than perlite), but the two are not always interchangeable, although as rooting mediums, both provide the same benefit.

Other uses of perlite include masonry construction, cement, gypsum plasters, and loose-fill insulation. Perlite is also used in pharmaceuticals and municipal swimming pool water filtration as well as an abrasive in polishes, cleansers, and soaps. 

Perlite Production

Perlite is a form of volcanic glass that is mined all over the world. It is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently. It is an industrial mineral and a commercial product useful for its low density after processing.

Perlite is mined using open pit methods such as ripping or blasting, or both. If the perlite is soft and friable, brecciated, or extensively jointed, ripping is employed with significant cost savings. Blasting is required where perlite cannot be readily broken using rippers, but care must be taken to achieve fragmentation without the production resulting in excessive fines or oversized material. 

Horticultural Perlite

While both perlite and vermiculite aid in water retention, perlite is more porous and tends to allow water to drain much more readily than vermiculite. This makes perlite a more suitable addition to potting soils for plants that do not require very moist media, such as cactus soils, or for plants that thrive in well-draining soil.

Horticultural perlite is made by exposing perlite to heat, which causes the trace water contained in the perlite to expand, "popping" the perlite like popcorn and expanding it to 13 times its former size. The final product is a very lightweight, white stone-like substance. The superheated perlite is comprised of tiny air compartments. This results in an incredibly lightweight material. The end product weighs only five to eight pounds per cubic foot. 

Under a microscope, perlite is revealed as being covered with many tiny cells that absorb moisture on the exterior of the particle, not inside, which makes it particularly useful in directing moisture to plant roots. Perlite is prized for its moisture retention and aeration properties. It is naturally sterile and has a neutral pH.

Potting Soil Mixtures With Perlite

Potting soil is used for container plants or starting young plants from cuttings or seedlings that need to become established before moving to the garden. Potting media is more coarse than garden soil and must allow moisture to reach tender roots but still drain away to prevent root rot.

Making potting soil at home is less expensive than purchasing pre-mixed bags and allows you to adjust the mixture to suit the characteristics of the plant.

Foliage Plants

• 2 parts peat
• 1 part perlite
• 1 part coarse sand

Succulents

• 2 parts soil
• 1 part peat moss
• 1 part perlite
• 1 part coarse sand
  

Fluoride Burn

Horticultural perlite is used as a component in soilless growing mixes, a growing medium for rooting cuttings, or as a hydroponic growing media. When growing plants in perlite, be aware that it may cause fluoride burn, which appears as brown tips on houseplants.