"Perlite for production, Pumice for presentation" is a statement I use fairly often. Perlite is wonderful stuff - it provides structure and it reduces the overall water-holding capacity of a mix because it doesn't hold water internally. However, it does not significantly improve drainage until it makes up the significant majority of the mix itself (approximately 70% or so).

Josh

What Josh said, though on a volume for volume basis, if you're trying to decrease o/a water retention in water-retentive soils, coarse grit gets the nod over perlite gets the nod over pumice, but there's the cost and weight factor of coarse grit to factor into the equation.

Al

Perlite is probably good for plants in pots, but when you grow stuff that's going in the ground, avoid it. Perlite is forever and it becomes unsightly unless you mulch over it.

Why do you prefer perlite to pumice, Al? I use both and find pumice infinitely easier to work with. Perlite sticks to everything, floats, stratefies, and breaks up so easily, while pumice holds its form, doesn't float nearly as much, and tends to stay put better. I'm increasingly impressed with pumice in mixes, and alone. You have more experience though, so I'd like to hear your opinion.

I have a little leaf-rooting experiment in progress with some Sedeveria leaves right now. They're rooting in 1) straight perlite, 2) straight pumice, and 3) 2:1 Grani-Grit to DE. Interestingly, the plantlets from the leaves in pumice and perlite are much larger than those in the granite/DE, and those in the perlite are the largest of any. The most rot occurred in granite/DE. It isn't an entirely fair experiment though because my variables aren't quite standardized: the pumice particles size is about 50% larger than the granite/DE, and the perlite particles are of mixed sizes. Also, the size of the leaves might affect plantlet growth, and finally, the perlite is a couple inches farther from the window than the granite/DE, which is a couple inches farther than the pumice.

Anyway, I'm still messing with perlite for various things, including rooting, so I'm also interested in the debate.

Just some thoughts:

I only use it (perlite) for the 5:1:1 mix, and I use it to reduce water retention. To that particular end, it's more effective than pumice because there is no internal porosity in perlite to hold water. I PREFER soils that require the grower to water more frequently because they generally offer greater opportunity for your plants to realize more of their potential, even if it requires the grower to extend a little more effort to water more often.

Chunky particles of Perlite, grit, Turface, pumice ...... are all more effective in bark soils than in soils based on small particles of peat, compost, coir, composted forest products, sand ...... The reason is, the particles get wedged in between the plate-like particles of bark, holding them apart and creating some quite large macro-pores between the bark pieces. The large particles in peaty soils simply get surrounded by the small particles, which is why the large particles don't do much for aeration/drainage in soils based on fine materials (peat, coir, compost, sand, topsoil .....) until the larger particles reach a threshold % of the overall volume of the soil.

Example: If you have a quart of marbles, all the same size, you can see all the wonderful air spaces in between the marbles. If you add a handful of marbles to a quart of peat, what's accomplished? Not much. If you keep adding marbles or any other chunky material, before you improve drainage or aeration, there must be a volume of marbles so large there isn't enough fine material in the soil to fill all the spaces between the larger particles. That is the threshold % at which the large particles start to make a significant difference.75-80%, usually.

That's also why I often note you really can't start with a peat based soil and amend it with perlite or other chunky material so you can water w/o concern about root function issues or root rot. It takes such a large % of large particles for it to work effectively (well over 50%) that by the time you get to a really effective soil it's no longer a peat soil you amended with large particles - it's a soil based on large particles you amended with peat.

If you're wanting a soil that A) eliminates worry about over-watering and associated problems, B) allows you easy and effective control over nutritional supplementation, start with a very large fraction (75-85%) of chunky material (pine bark, Turface, pumice, calcined DE, Haydite, poultry grit ..... and add a small fraction of fine material to adjust water retention so the frequency at which you need to water is something you can live with.

I think when debates get going with some degree of passion, it's usually because one grower is looking at things from the perspective of what's better for the grower in terms of effort expended or costs, while another grower approaches things from the perspective of what it takes to ensure the plant's best opportunity to realize as much of its potential as possible. There is no right or wrong way to order those priorities, but which perspective is in play can have a significant impact on how we approach our growing efforts.

Al