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. -- Rodger Whitlock Victoria, British Columbia, Canada Z. 7-8, cool Mediterranean climate