Soil: TOH landscape contractor Roger Cook sets posts on a 6-inch base of ¾-inch crushed stone to encourage drainage. Then he fills around posts with the soil from the holes, minus the topsoil, and packs it down every 6 inches. In sandy soil, he mixes in gravel so that it will pack more firmly. In clay soil, which doesn't drain well, he packs only gravel around posts.
Concrete: Roger uses concrete only for gateposts or when rock stops him from digging deep enough, one-third of the post's length. Concrete is costly—each post requires two or three $5 bags—and slow,
as posts must be braced until the concrete sets.