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. However, as rooting mediums, both provide the same benefit.

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, resulting in an incredibly lightweight material.

Under a microscope, perlite is revealed as being covered with many tiny cells that absorb moisture on the exterior of the particle, not inside. This 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.

How Perlite Differs From Vermiculite

Perlite is that white material in soilless potting mixes that looks like little chunks of styrofoam. In its natural state, it has a pearl-like shine to it that accounts for the name, "perlite." While vermiculite and perlite are two completely different substances, they do have some things in common. Both are:

• Mined out of the ground (perlite is a volcanic mineral)
• Later heated, causing them to expand
• Used as soil amendments, both in soilless potting mixes indoors and to improve garden soil outdoors
• Lightweight
• Sterile
• Have a neutral pH
• Contain no nutrients

However, while vermiculite is especially valued for its capacity to retain water, the value of perlite lies much more in its ability to provide aeration.

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. 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 & Cacti:

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