Thank you Rodger. That is most interesting. Where I live the soil is volcanic and plants love it. I didn't connect the fact of that with the pumice I now use in containers. I have done no horticultural training, just a gardener from a young age. And get a feel of what agrees with them and what doesn't. Great to know your info on this. Ina Crossley On 22/10/2015 8:42 a.m., Rodger Whitlock wrote: > On 21 Oct 2015, at 16:01, Hans Huizing wrote: > >> I also use Pumice. >> For the more difficult Cyrtanthus species I use pure Pumice 2-5 mm. >> The root system develops very well in this material. > A demonstration that plant roots need air too. And I don't mean just epiphytes. > >> Since this material contains no nutrients... > Pumice (volcanic pumice) is nutrient-rich like other volcanic ejecta. Think > about the slopes of Mt. Vesuvius, which have been farmed for millenia because > the soil (decomposed ejecta) is so rich. Particularly rich in potassium, I > understand. The best part is that the nutrients in pumice are released slowly.