Compact the trench
Lay a crushed stone base
Our experts prefer crushed stone for the base rather than naturally occurring gravel dug from a pit. Crushed stone is a little more expensive. However, it provides better drainage, and because of the sharper angles on the stone, it requires less compacting, and once it's compacted, it stays that way.
Joe and Jake have found that crushed stone sized between 1/2 in. and 3/4 in. is best suited to handle the heaving forces created by the harsh freeze/thaw cycles here in Minnesota. Avoid rounded stones like pea gravel or river rock; they don't form strong interlocking bonds like angular stone.
Leave the stone no more than 1/2 in. higher than you want the final height to be, and then make a couple passes with a hand tamper or plate compactor. You'll notice the stone is almost 100 percent compacted as soon as it's laid in the trench. The same type of stone will be used for backfilling, which also eliminates the need for hauling in multiple materials.