I add leaf mould, as a matter of routine, when potting snowdrops, daffodils, Crocus, reticulate Iris (prone to 'Ink spot' fungus), freesias, and some other genera. It certainly improves their growth in my conditions. I had assumed that these bulbs benefit from the extra moisture retained while in growth and that this also helps maintain consistent moisture levels necessary to maintain strong shoot growth in cormous plants, which enter premature dormancy very easily in drought conditions. I am definitely prepared to accept that the benefits may be mycorrhizal at least in part. Peter (UK)