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.
Without deviation from the norm, progress is not possible - Zappa. Tiny ad:
Binge on 17 Seasons of Permaculture Design Monkeys!