When preparing to dig a trench, water the ground approximately two days before you dig to soften the soil. The climate in your area can determine how deep to dig the trench. Cold climates where hard freezes occur require a trench to be at least 18 inches. In extremely cold climates consult an irrigation contractor or supplier to determine how deep to dig below the frost line. Mild climates can be made at a depth of 8-12 inches. Check out some of our recommended shovels by clicking here.