I have mostly smaller pots so I buy the 1/8" size. I think the larger size would dry out faster, so for pots outside in the rain, or bigger pots, or if you are a compulsive waterer, then the larger size would be better.

I use an equal mix of pumice sand and 3-7mm pumice for all my potting needs, including 50mm pots. Has worked for me for decades...

Robin,

Sounds like we agree on the basic principle behind using more or less uniformly-sized potting media so perhaps I can just share some benchmark in case you'll find them useful:

I use 3/16ths for big plants in big pots (i.e. gasterias, adult adeniums). I also use it for by bigger haworthias though, that are in smaller pots, because they have fat roots that will disintegrate if wet for too long.

But I have more use for 1/8ths too, because most of my plants are tiny, planted in tiny pots--adromischus, crassulas, avonias, mesembs, othonas, tylecodons all have wispy feeders that will desiccate if the air spaces in my substrate are too large.

I grew my sans in a similar substrate you described and it did well even with the fine particles. I believe it is because they aren't really averse to being watered profusely. They will tolerate arid conditions but if they are watered heavily during growing season, they do take off.

Thanks to everyone. Pagan, as you suggest, I think I will remain with my 1/8" pumice. Most of my plants are small, and for the handful in larger pots -- they seem to adjust. Perhaps it is because the pumice is only one of 3, 4 or even more components for the bigger-pot plants. Thanks again, everyone.

I have some African succulent trees, and in summer in larger grits I could water twice a day, too much for me. The 1/8" and watering only once per day is much more my style, though I could also keep the larger grit and just add in some rough sphagnum to increase water retention...

ez