as a method of "hugelkultur", by putting them in the soil either under or around whatever you are planting, hollow side up. This would create little "buckets" to hold water, and slowly rot away over time, normally by which time the tree will be more able to retrieve its water from deeper in the subsoil. Cheers.
We find this kind of rampant individuality very disturbing. But not this tiny ad:
A rocket mass heater is the most sustainable way to heat a conventional home