From a reader:
Having entered Holy Week I’m confronted with an annual problem. What do we do with blessed Palms received on Palm Sunday, or the crosses made with them? They dry out through the week and, inevitably, pile up through subsequent house cleanings since I’m loathe to put them in the bin. What, then, is the best way to dispose of blessed Palms?
Old palms ought to be burned.
As a matter of fact the ashes used on Ash Wednesday are traditionally from the burned palms from the year before.
You can burn them yourself and if nothing else mix the ashes with water and pour them on the ground.
Hmmm… do ashes help plants?
Otherwise, perhaps your parish priest would take them and, when they burn the palms for Ash Wednesday for next year, your palms might be included.