Hi:
The dynamic of water in motion has been studied long ago. If you use layers of different materials, one on top of the others, water will collect in the transition zone between two layers before moving on down to the next lower layer. This will make a water layer that will greatly impede drainage as part of it will return tothe upper layer by capillarity. Thus, it is far more effective to mix two or more ingredients uniformly (provided they are suitable to improve drainage of the mix) than putting the same ingredients in layers.
Ditto, there is a different matter and is the method of filling the lower 1/3 of a pot with a well drained mix and then complete the volume with pure grit, coarse sand, etc. . The bulb, corm, etc. must be planted in the middle of this grit or gravel layer. The active roots will go down into the lower 1/3 for moisture and nutrients. This gives fantastic results for difficult bulbous plants as Zephyra elegans, Cyanella cygnea, Chilean Rhiodophialas, Chlidanthus, Tritonia watermeyeri, the Karoo Babianas and Lachenalias, Ungernias, Junos, Hyeronimiellas, Ismene amancaes and many others and also for non bulbous plants as the mesembs, Oncocyclus and Regelia irises, etc., etc. .
Best regards
Alberto
" I was wondering if anyone can tell me if there is any advantage to using> the potting> > mix only in the lower part of the container. Then placing the bulbs on the> top of the> > potting mix and use some small gravel ( or like material ) to cover the> bulbs to their> > appropriate depth."
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