Bulk bag of perlite
What is perlite?

Come propagation time (which of course can be almost anytime) and you may well find yourself walking along the isles of your local garden center asking yourself,

 '...what the flipping heck is perlite...?'

Green bags filled with what looks like white stone chippings seem to mock your ignorance. Especially when you pick it up to find out more and realize that the bag is empty! Ok, not so much empty, just very, very light.

Image credit to www.perlite.net
Put simply, perlite is an additive used to improve aeration and drainage in rooting mediums, usually a commercial grade compost. A quality that is particularly useful when it comes to propagating plants from seeds and cuttings

It turns out that perlite is a unique volcanic mineral which expands to about 13 times its original volume when it is heated to a temperature of approximately 1600 Fahrenheit - 871 Celsius. During the heating process, the mineral particles pop like popcorn and form a granular, snow-white material that is so light in weight it weighs only about 5 to 8 pounds per cubic foot (80-128 kg/cubic meter).

Image credit - stewardchem.com
Each particle of perlite is comprised of tiny closed air cells or bubbles. The surface of each particle is covered with tiny cavities which provide an extremely large surface area.

These surface cavities trap moisture and make it available to plant roots. In addition, because of the physical shape of each particle or perlite, air passages are formed in the growing media thereby providing excellent aeration.

Horticultural perlite is available in several different grades. The coarse sand size has been used for many general gardening and horticultural applications, but the finer grades work best when used outdoors.

So now you know.

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What is Perlite?
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