Is unexpanded perlite useful in any way?

Question

When I buy perlite, I immediately soak it in water and avoid inhaling the dust. I place it in a bucket and open the tap above it. This strong water flow stirs the perlite and the medium is wetted evenly. I then scoop the perlite with a sieve under the water flow and wash away the dust. Naturally, what I scoop is the puffed-up perlite which floats to the surface. However, there is some denser grain, unexpanded perlite, which sinks to the bottom of the bucket. It is grey and has a coarse grain, much like river sand or builder's sand. The grains are much larger than those of beach sand, for instance.

I used to throw this away in the past. The amount of coarse material I get from 10 liters of perlite is just enough to fill a cup, so I did not bother. Most of the time a mix with perlite in it is available without doing the extra effort, so buying perlite to make my own potting mix is not always necessary. However, I'm curious to know more about the unexpanded perlite. Does it have some air and water retention properties? Is it a good potting medium on its own, or mixed with other ingredients?

Answer 1

The coarse material you're seeing is unexpanded perlite (UXP) as you pointed out. It's not as useful as expanded perlite as a general soil amendment, but it does have some niche uses. Even in it's unexpanded form, it has good water retention an aeration qualities that are desirable in some circumstances.

For example, I found this post that suggests that it can be used as a replacement for natural pumice in a potting mix for growing bonsai trees, cactus, or other succulents. Also, here's a link where they sale UXP for that very purpose. Expanded perlite is more difficult to use for growing succulents because it tends to be too light and it floats to the surface.

There are also industrial uses for unexpanded perlite, but that is outside the scope of the question.