I have always preferred unwashed pumice with fines for my bulb and alpine mixes. In addition to retaining moisture, the fines also release a significant amount of nutrient and help to balance the pH of what would otherwise be a pretty acidic soil, given what is available to us here. Washed pumice is also available here but it's mostly used in bark-based coarse potting mixes for growing conifers and other woody plants. Jane McGary Portland, Oregon