I tend to throw the leaves in the firepit just. Could compost them probably. Not sure if toxins will build up in the soil from composting them.What do you do with the rhubarb leaves?
A couple ladies at my cooking class recommended to use the rhubarb leaves as top mulch/weed block for the garden. Just cut off the leaves and leave them in the garden. I'm sure it would block the weeds, but I wonder if it would block the rain as well. All the top mulch I have ever used (wood chips, dried grass clippings, leaves, unfinished compost) always had easy drainage. I just don't see that possible with large rhubarb leaves, but maybe it works OK.